Lesson 9 : Heredity and Evolution

9. Heredity and Evolution  

Traits  

Types of Traits  

Phenotype, Genotype and Allele  

Laws of Inheritance  

Rule for Inheritance  

Sex Determination  

Speciation and Geographic Isolation  

Types of Speciation  

Theory of Natural Selection  

Homologous and Analogous Characteristics  

Evolution by Stages

 Lesson: Heredity and Evolution

Question: 1

A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as:

(a) TTWW

(b) TTww

(c) TtWW

(d) TtWw

Solution:

(c)

Question: 2

An example of homologous organs is:

(a) Our arm and a dog’s fore-leg

(b) Our teeth and an elephant’s tusks

(c) Potato and runners of grass

(d) All of the above

Solution:

(b)

Question: 3

In evolutionary terms, we have more in common with:

(a) A Chinese school-boy

(b) A chimpanzee

(c) A spider

(d) A bacterium

Solution:

(a)

Question: 4

A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light-coloured eye trait is dominant or recessive? Why or why not?

Solution:

This information is not sufficient. For considering a trait as dominant or recessive, we need data of at least three generations. But the study gives the data of only two generations.

Question: 5

How are the areas of study —$$ evolution and classification —$$ interlinked?

Solution:

Classification is based on similarities and differences amongst organisms.

Two species are more closely related if they have more characteristics in common. It means that they have a more recent ancestor. With subsequent generations, variations make organisms more different than their ancestors.

This proves that we classify organisms according to their resemblance, which is similar to creating an evolutionary tree.

Also, the modern system of classification is otherwise called phylogenetic classification. This means it is based on evolutionary relationships. Hence, evolution and classification are closely related.

Question: 6

Explain the terms analogous and homologous organs with examples.

Solution:

Homologous organs are the organs that have same basic structural design and origin but have different functions.

Example: The forelimbs of humans and the wings of birds

Analogous organs are the organs which have different basic structural design and origin but have similar functions.

Example: The wings of birds and insects.

Question: 7

Outline a project that aims to find a dominant coat colour in dogs.

Solution:

Dogs have a variety of genes that govern coat colour. A dog inherits one gene from each of his/her parents and the dominant gene gets expressed in the phenotype. Let us take one parent with black coat (B) and the other parent with brown coat (b).

Situation 1: Crossing to get the F1 generation.

In F1 generation, all the offspring’s will be heterozygous (Bb). Since black (B) is dominant, all the offspring’s will be black. However, they will have both B and b alleles.

Situation 2: Crossing the heterozygous pups to get the F2 generation.

The F2 generation will produce 25% homozygous black (BB), 50% heterozygous black (Bb), and 25% homozygous brown (bb) offspring’s.

Question: 8

Explain the importance of fossils in deciding evolutionary relationships.

Solution:

Fossils are preserved traces of living organisms.

Important features of fossils:

(a) Fossils help in determining the sequence of appearance of a particular character in a particular group of species.

(b) Fossils help in establishing evolutionary traits among organisms and their ancestors.

(c) Fossils help in establishing the time period in which a particular species lived.

Question: 9

What evidence do we have for the origin of life from inanimate matter?  

Solution:

An experiment done by Miller and Urey established that life originated from inanimate matter. In their experiment, they replicated conditions which may have existed during the early years of the origin of Earth. In that experiment, inorganic substances gave rise to amino acids. As we know, amino acids make up protein molecules and support life in its basic form. Therefore, it adequately suggests that life originated from inanimate matter.

Question: 10

Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?

Solution:

During sexual reproduction, genotype of a progeny is contributed by two different individuals. This results in various permutations and combinations.

Whereas in case of asexual reproduction, only very small variations pass on to the progeny. This is mainly due to inaccuracies in DNA copying.

Thus, offspring of asexual reproduction are more or less genetically similar to their parents. Therefore, there are more chances of variations during sexual reproduction than during asexual reproduction. Due to this reason, the evolution in sexually reproducing organisms proceeds at a faster pace than in asexually reproducing organisms.

Question: 11

How is equal genetic contribution of male and female parents during fertilisation of a progeny?

Solution:

Human female has two X sex chromosomes and male has one X and one Y sex chromosome. During fertilization, the male gamete (haploid) fuses with the female gamete (haploid). This results in formation of the diploid zygote. The zygote gets 50% of genes from each parent. Thus, equal genetic contribution is ensured from the male and female parents during fertilization.

Question: 12

Only those variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not? 

Solution:

Yes. We agree with the statement. All variations do not have an equal chance of surviving in the environment. The chances of surviving depend on the nature of variations. There are many variations which help an individual to survive. But there are certain variations which may not be beneficial, yet they are inherited through subsequent generations.

For example, the colourful plumage of peacock helps a peacock in finding a suitable mate but it is also eye-catching for its predators.

Lesson: Heredity and Evolution

Question: 1

Exchange of genetic material takes place in:

(a) Vegetative Reproduction

(b) Asexual Reproduction

(c) Sexual Reproduction

(d) Budding

Solution:

(c)

Question: 2

Two pink coloured flowers on crossing resulted in 1 red, 2 pink and 1 white flower progeny. The nature of the cross will be:

(a) Double Fertilisation

(b) Self Pollination

(c) Cross Fertilisation

(d) No Fertilisation

Solution:

(b)

Question: 3

A cross between a tall plant (TT) and short pea plant (tt) resulted in progeny that were all tall plants because:

(a) Tallness is the dominant trait

(b) Shortness is the dominant trait

(c) Tallness is the recessive trait

(d) Height of pea plant is not governed by gene ‘T’ or ‘t’

Solution:

(a)

Question: 4

Which of the following statement is incorrect?

(a) For every hormone there is a gene.

(b) For every protein there is a gene.

(c) For production of every enzyme there is a gene.

(d) For every molecule of fat there is a gene

Solution:

(d)

Question: 5

If a round, green seeded pea plant (RRyy) is crossed with wrinkled, yellow seeded pea plant, (rrYY) the seeds produced in F1 generation are:

(a) Round and yellow

(b) Round and green

(c) Wrinkled and green

(d) Wrinkled and yellow

Solution:

(a)

Question: 6

In human males, all the chromosomes are paired perfectly except one. This/this unpaired chromosome is/ are:

(i) Large chromosome

(ii) Small chromosome

(iii) Y- chromosome

(iv) X- chromosome

(a) (i) and (ii)

(b) (iii) only

(c) (iii) and (iv)

(d) (ii) and (iv)

Solution:

(c) 

Question: 7

The maleness of a child is determined by:

(a) The X chromosome in the zygote

(b) The Y chromosome in the zygote

(c) The cytoplasm of germ cell, determines the sex

(d) Sex is determined by chance

Solution:

(b)

Question: 8

A zygote which has an X-chromosome inherited from the father will develop into a:

(a) Boy

(b) Girl

(c) X- chromosome does not determine the sex of a child

(d) Either boy or girl

Solution:

(b)

Question: 9

Select the incorrect statement:

(a) Frequency of certain genes in a population, change over several generations resulting in evolution.

(b) Reduction in weight of an organism, due to starvation is genetically controlled.

(c) Loss-weight parents can have heavy weight progeny.

(d) Traits which are not inherited over generations, do not cause evolution.

Solution:

(b)

Question: 10

New species may be formed if:

(i) DNA undergoes significant changes in germ cells

(ii) Chromosome number changes in the gamete

(iii) There is no change in the genetic material

(iv) Mating does not take place

(a) (i) and (ii)

(b) (i) and (iii)

(c) (ii), (iii) and (iv)

(d) (i), (ii) and (iii)

Solution:

(a)

Question: 11

Two pea plants one with round green seeds (RRyy) and another with wrinkled yellow (rrYY) seeds produce F1 progeny that have round, yellow (RrYy) seeds. When F1 plants are selfed, the F2 progeny will have new combination of characters. Choose the new combination from the following:

(i) Round, yellow

(ii) Round, green

(iii) Wrinkled, yellow

(iv) Wrinkled, green

(a) (i) and (ii)

(b) (i) and (iv)

(c) (ii) and (iii)

(d) (i) and (iii)

Solution:

(b)

Question: 12

A basket of vegetables contains carrot, potato, radish and tomato. Which of them represent the correct homologous structures?

(a) Carrot and potato

(b) Carrot and tomato

(c) Radish and carrot

(d) Radish and potato

Solution:

(c)

Question: 13

Select the correct statement:

(a) Tendril of a pea plant and phylloclade of Opuntia are homologous

(b) Tendril of a pea plant and phylloclade of Opuntia are analogous

(c) Wings of birds and limbs of lizards are analogous

(d) Wings of birds and wings of bat are homologous

Solution:

(a)

Question: 14

If the fossil of an organism is found in deeper layers of earth, then we can predict that:

(a) The extinction of organism has occurred recently.

(b) The extinction of organism has occurred thousands of years ago.

(c) The fossil position in the layers of earth is not related to its time of extinction.

(d) Time of extinction cannot be determined.

Solution:

(b)

Question: 15

Which of the following statements is not true with respect to variation?

(a) All variations in a species have equal chance of survival.

(b) Change in genetic composition results in variation.

(c) Selection of variants by environmental factors, forms the basis of evolutionary processes.

(d) Variation is minimum in asexual reproduction.

Solution:

(a) 

Question: 16

A trait in an organism is influenced by:

(a) Paternal DNA only

(b) Maternal DNA only

(c) Both maternal and paternal DNA

(d) Neither by paternal nor by maternal DNA

Solution:

(c) 

Question: 17

Select the group which shares maximum number of common characters

(a) Two individuals of a species

(b) Two species of a genus

(c) Two genera of a family

(d) Two genera of two families

Solution:

(a) 

Question: 18

According to the evolutionary theory, formation of a new species is generally due to:

(a) Sudden creation by nature

(b) Accumulation of variations over several generations

(c) Clones formed during asexual reproduction

(d) Movement of individuals from one habitat to another

Solution:

(b) 

Question: 19

From the list given below, select the character that can be acquired, but not inherited:

(a) Colour of eye

(b) Colour of skin

(c) Size of body

(d) Nature of hair

Solution:

(c)

Question: 20

The two versions of a trait (character) that are brought in by the male and female gametes are situated on:

(a) Copies of the same chromosome

(b) Two different chromosomes

(c) Sex chromosomes

(d) Any chromosome

Solution:

(a)

Question: 21

Select the statements that describe characteristics of genes:

i) Genes are specific sequence of bases in a DNA molecule.

ii) A gene does not code for proteins.

iii) In individuals of a given species, a specific gene is located on a particular chromosome.

iv) Each chromosome has only one gene.

(a) (i) and (ii)

(b) (i) and (iii)

(c) (i) and (iv)

(d) (ii) and (iv)

Solution:

(b)

Question: 22

In peas, a pure tall plant (TT) is crossed with a short plant (tt). The ratio of pure tall plants to short plants in F2 is:

a)      1: 3

b)      3: 1

c)      1: 1

d)      2: 1

Solution:

(c)

Question: 23

The number of pair (s) of sex chromosomes in the zygote of humans is:

(a)   One

(b)   Two

(c)   Three

(d)   Four

Solution:

(a)

Question: 24

The theory of evolution of species by natural selection, was given by:

(a) Mendel

(b) Darwin

(c) Morgan

(d) Lamarck

Solution:

(b)

Question: 25

Some dinosaurs had feathers although they could not fly, but birds have feathers that help them to fly. In the context of evolution this means that:

(a) Reptiles have evolved from birds.

(b) There is no evolutionary connection between reptiles and birds.

(c) Feathers are homologous structures in both the organisms.

(d) Birds have evolved from reptiles.

Solution:

(d)

Question: 26

How sex of a new-born is determined in humans?

Solution:

Sex of a new born human is genetically determined i.e., genes inherited from parents decide whether the new born will be a boy or a girl. If a father’s sperm with X chromosome fertilizes the mother’s egg, it results in development of a girl child. Whereas, if a sperm with Y chromosome fertilizes the egg, it results in the development of a male child.

Question: 27

Do genetic combinations of a mother play a significant role in determining the sex of a new born?

Solution:

No, it does not. Mothers have a pair of X-chromosomes. Sex of a new-born is determined by the 23^rd chromosome in the sperm. All children inherit an ‘X’ chromosome from their mothers regardless of whether they are boys or girls. So, the genetic combination of a mother has no role in determining the sex of a new born.

Question: 28

Mention three important features of fossils that help in study of evolution.

Solution:

Fossils preserved traces of living organisms. The three important features of fossils are given below.

(a) It helps in determining the sequence of appearance of a particular character in a particular group of species.

(b) It helps in establishing evolutionary traits among organisms and their ancestors.

(c) It helps in establishing the time period in which a particular species lived.

Question: 29

Why do all the gametes formed in human females have an X chromosome?

Solution:

Human females have two X chromosomes called sex chromosomes. During gametogenesis, one X chromosome enters each gamete. Hence all the gametes formed in human female possess an X chromosome. 

Question: 30

In human beings, the statistical probability of getting either a male or a female child is 50:50. Give a suitable explanation.

Solution:

A somatic cell in human male has XY chromosomes. If one gametocyte undergoes meiosis, it produces two sperms. In which one sperm gets X chromosome and another gets Y chromosome. Since the ratio of male gametes containing X chromosome and those containing Y chromosome is 50:50, the statistical probability of male or a female infant is also 50:50.

Question: 31

A smaller population of a species faces greater threat of extinction than a larger population. Provide a suitable genetic explanation.

Solution:

Limited number of individuals in a species imposes extensive inbreeding, resulting in negligible variations through successive generations. Since the number of individuals is small, the population is always exposed to the dangers of sudden changes in environment. In many such cases, individuals fail to cope up with the environmental changes, therefore they become extinct.

Question: 32

What are homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor?

Solution:

Homologous structures have a common basic design but perform different functions.

Example: The fore limbs of reptiles, amphibians and mammals have common ancestor, but are variously modified to carry out different activities.

Yes, it is necessary that homologous structures always have a common ancestor.

Question: 33

Does the occurrence diverse animals on Earth, also suggest their diverse ancestry? Discuss this point in light of evolution.

Solution:

No, diversity of animals on Earth does not suggest their diverse ancestry. Animals have a vast diversity in structures on Earth that is based on certain common characters. We can group these animals into different groups and subgroups. For example, all animals without notochord are grouped under invertebrates.

Question: 34

Given the pair of contrasting traits of the following characters in pea plant and mention which is dominant and recessive.

(i) Yellow seed

(ii) Round seed

Solution:

Green seed is the contrasting trait of yellow seed.

Wrinkled seed is the contrasting trait of round seed.

        i.            Yellow —$$ dominant

Green —$$ recessive

      ii.            Round —$$ dominant

Wrinkled —$$ recessive

Question: 35

Why did Mendel choose pea plant for his experiments?

Solution:

Mendel chose pea plants for the following reasons.

(a)   It is easy to grow

(b)   It has short life span. This helps in conducting many experiments in a short period.

(c)   It has easily distinguishable characteristics.

(d)   It has large size flowers.

(e)   It undergoes self-pollination.

Question: 36

A woman has only daughters. Analyse the genetic situation and provide a suitable explanation.

Solution:

Birth of a male or female child depends on the presence of X or Y chromosome in the sperm that fertilizes the egg. Therefore, the father genetically contributes towards the birth of a girl child or a male child.

Question: 37

Does geographical isolation of individuals of a species lead to formation of a new species? Provide a suitable explanation.

Solution:

Yes, geographical isolation of individuals of a species leads to the formation of a new species. Geographical isolation, initially imposes limitations for sexual reproduction of the separated population, thereby leading to a gradual genetic drift.

Slowly, the separated individuals start reproducing among themselves and generate new variations. Continuous accumulation of those variations for a few generations may ultimately lead to the formation of a new species.

Question: 38

Bacteria have a simpler body plan when compared with human beings. Does it mean that human beings are more evolved than bacteria? Provide a suitable explanation.

Solution:

Evolution cannot always be equated with progress or better body designs. So, it does not mean that simple body designs are inefficient. When we take complexity of a body design as a criterion for evolution, then human beings are more evolved than bacteria.

On the other hand, if we take the ability to survive in almost all kinds of habitat as a criterion; bacteria, having a simple body design, are still the most evolved organisms found on earth. From this perspective, bacteria appear to be more evolved than human beings.

Question: 39

All human races like Africans, Asians, Europeans, Americans and others might have evolved from a common ancestor. Provide a few evidences in support of this view.

Solution:

All human beings on this earth have the capability to interbreed. This shows that all of them belong to the same species, and they all show maximum number of common characters. Some of the common characters in human beings are as follows:

·         Similar size of the brain

·         Same body design

·         Bipedal locomotion

·         Hair on body

·         Ability to communicate using language

·         Social behaviour

Similarity in traits indicates common ancestry for all human beings.

Question: 40

Differentiate between inherited and acquired characters. Give one example for each type.

Solution:

Inherited characters	Acquired characters
Traits that are passed on from parents to offspring.	Traits that appear in an individual’s lifetime, but cannot be transmitted to the next generation.
Traits alter the genotype and phenotype.	Traits that alter only the phenotype.
Traits are the result of genetic recombination.	Traits that are the result of individual’s response to environmental challenges.
Examples: Hair colour, eye colour, skin colour, seed colour, etc.	Examples: Muscular body, loss of a body part in an accident, hair loss, etc.

Question: 41

Give reasons why acquired characters are not inherited.

Solution:

Acquired characters appear in an individual because of his/her response to external stimuli. These characters do not produce any change in the DNA of the germ cells. Only those characters that have a gene for them can be inherited. Since there is no gene for the acquired characters, they cannot be inherited.

Question: 42

Evolution exhibits a greater stability of molecular structure when compared with morphological structures. Comment on the statement and justify your opinion.

Solution:

Morphological structures can be easily seen by us. Life began as a simple form of unicellular organisms. Gradually, it evolved into many complex organisms. Whatever diversity we see around us, is because of the diversity in the morphological structure such as size, form and other morphological features. Thus, it can be said that morphological structures show least stability.

On the other hand, molecular structures are found at the molecular level. All the organisms are made up of same biomolecules such as DNA, RNA, protein, lipid, carbohydrates, etc. Even though, the number of biomolecules varies from organism to organism, their structures remain the same in every organism.  Hence, it can be said that molecular structures show greater stability when compared to the morphological structures.

Question: 43

In the following crosses write the characteristics of the progeny.

Cross	Progeny
(a) RR YY                      x              RR YY     Round, yellow                        Round, yellow$$	........................... ...........................
(b) Rr Yy                      x              Rr Yy     Round, yellow                      Round, yellow$$	........................... ...........................
(c) rr yy                      x              rr yy     Wrinkled,  green                   wrinkled,  green$$	........................... ...........................
(d) RR   YY                            x          rr yy     Round, yellow                           wrinkled,  green$$	........................... ...........................

Solution:

(a) RRYY    Round, yellow

(b) RRYY   Round, yellow

     RrYy      Round, yellow     

     RRyy      Round, green

     Rryy       Round, green

     rrYY      Wrinkled, yellow

     rrYy       Wrinkled, yellow

     rryy        Wrinkled, green

(c) rryy         Wrinkled, green

(d) RrYy       Round, yellow

Question: 44

Study the following cross showing self-pollination in F1, and fill in the blank and answer the question that follows:

Parents        RRYY                   x             rryy

                   Round, yellow                      wrinkled, green

     F1          RrYy                      x             ?

                   Round, yellow

Solution:

RrYy Round, yellow

Question: 45

In question 44, what are the combinations of character in the F2 progeny? What are their ratios?

Solution:

I. Round yellow (RRYY) and (RrYy) —$$ 9

II. Round green (RRyy) and (Rryy) —$$ 3

III. Wrinkled yellow (rrYY) and (rrYy) —$$ 3

IV. Wrinkled green (rryy) —$$ 1

This can be shown by the following Punette Square:

The ratio is 9: 3: 3: 1

Question: 46

Give the basic features of the mechanism of inheritance.

Solution:

Characters are controlled by genes. Each gene controls one character. There may be two or more forms of genes. One form may be dominant over the other. These genes are present in DNA. DNAs; in turn are present in the form of chromosomes. Every trait is present in pairs, i.e. alleles. Out of a pair of contrasting traits, one is present in a particular chromosome and the other in another chromosome. This ensures that, when gametes are formed, one trait goes to one gamete and another goes to the other one. This forms the basis of the law of segregation as proposed by Mendel.

In his monohybrid, cross experiment, Mendel crossed a pure-bred tall plant with a pure-bred short plant. In F1 generation, the gene governing the tallness dominated. So, the all the plants in F1 generation were tall. However, in F2 generation, some plants were tall while others were short. This could be possible because of recombination of gametes during fertilization.

Question: 47

Give reasons for the appearance of new combinations of characters in the F2 progeny.

Solution:

Appearance of a new combination of characters in F2 progeny can be explained by illustrating dihybrid cross as was carried out by Mendel.

During the dihybrid cross, Mendel crossed the pure bred of tall plants having round seeds with pure bred of short plants having wrinkled seeds. It was observed that all the F1 generation plants were tall with round seeds. This indicated that the traits of tallness and round seeds were dominant. However, genes for recessive traits were present in all the plants.

Later, the self-breeding of F1 generation seeds yielded F2 generation. The F2 generation plants had the characters of tall with round seeds (9 plants), tall with wrinkled seeds (3 plants), short with round seeds (3plants) and short with wrinkled seeds (1 plant). The tall-wrinkled seeds and short-round seeds were the new combination, which developed only when the traits were inherited independently.

Lesson: Heredity and Evolution

Question: 1

If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?

Solution:

Trait B is likely to have arisen earlier because it is present in a higher percentage of the population.

Question: 2

How does the creation of variations in a species promote survival?

Solution:

Variations in a species take place in response to the changes in the environment. This enables a species to cope with new changes. Depending on the nature of variations, different individuals would have different kinds of advantages. For example, bacterial variants that can withstand heat have better chances to survive a heat wave than the non-variant bacteria. Thus, variations in a population of a species help in survival of a species.

Question: 3

How do Mendel’s experiments show that traits may be dominant or recessive?

Solution:

During monohybrid cross by conducted by Mendel, one trait did not appear in the F1 generation. However, it appeared in the F2 generation obtained by self-fertilization of the F1 generation.

From his experiment, he concluded:

a)      The trait which appeared in all the members of F1 generation and in 75% members of the F2 generation was a dominant trait.

b)      The trait which did not appear in F1 generation but reappeared in 25% of F2 generation was a recessive trait.

Question: 4

How do Mendel’s experiments show that traits are inherited independently?

Solution:

During dihybrid cross, Mendel crossed the pure-bred tall plants having round seeds with pure bred short plants having wrinkled seeds. It was observed that all the F1 generation plants were tall with round seeds. This indicated that the traits of tallness and round seeds were dominant.

Later, the self-breeding of F1 generation seeds yielded F2 generation. The F2 generation plants had characteristics of tall with round seeds (9 plants), tall with wrinkled seeds (3 plants), short with round seeds (3 plants) and short with wrinkled seeds (1 plant). The tall wrinkled seeded and short round seeds were the new combinations. This could develop only when the traits were inherited independently. Thus, Mendel was able to propose the law of independent assortment which explains independent inheritance of traits.

Question: 5

A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits –$$ blood group A or O –$$ is dominant? Why or why not?

Solution:

No. This information is not sufficient to determine which of the traits is dominant or recessive. We need data of at least three generations whereas the given data is about two generations.

Question: 6

How is the sex of the child determined in human beings?

Solution:

The sex of a new-born in human is genetically determined i.e., genes inherited from parents decide whether the new born will be a boy or a girl. If a sperm with X chromosome fertilizes the egg, it results in the development of a girl child. Whereas, if a sperm with Y chromosome fertilizes the egg, it results in the development of a male child.

Question: 7

What are the different ways in which individuals with a particular trait may increase in a population?

Solution:

Individuals with a particular trait may increase in a population:

·         When a trait is acquired during the individual's lifetime

·         When some genes governing the trait become common in a population

·         When the trait offers some survival advantage

Question: 8

Why are the traits acquired during an individual’s lifetime, not inherited?

Solution:

Acquired traits do not bring any change in the genotype of an individual. Therefore, these traits are not inherited.

Question: 9

Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?

Solution:

Variations are essential to the survival of a species. The small number of surviving tigers does not allow many variations to occur. A deadly disease or any calamity may cause death of all the tigers. Hence, a small number of surviving tigers is a cause of worry.

Question: 10

What factors could lead to the rise of a new species?

Solution:

Natural selection, genetic drift and acquisition of traits during the life time of an individual can give rise to new species.

Question: 11

Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?

Solution:

In self-pollinating plant species, pollens are transferred from the anther of one flower to the stigma of the same flower or another flower of the same plant.

So, geographical segregation cannot be a major factor in speciation. However, there are chances of some environmental changes that can lead to some variations.

Question: 12

Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?

Solution:

No. Asexually reproducing organisms pass on the parent DNA to offspring that leaves no chance of speciation. Hence, geographical isolation does not affect much in asexually reproducing organisms. However, geographical isolation may work as a major factor in cross-pollinated species.

Question: 13

Give an example of characteristics being used to determine how close two species are in evolutionary terms.

Solution:

A few ancient reptiles such as dinosaurs had feathers. However, they could not fly with those feathers. The feathers were used only to provide insulation in cold weather. Later, birds adapted the feathers for flight. This means that birds are very closely related to reptiles, as dinosaurs were reptile.

Question: 14

Can wings of a butterfly and wings of a bat be considered homologous organs? Why or why not?

Solution:

Wings of bats are skin folds stretched mainly between elongated fingers. The wings of birds are a feathery covering all along the arm. Wing of a butterfly and the wings of a bat are similar in function. They help them in flying. Since they perform similar function and have different origins, they are analogous organs.

Question: 15

What are fossils? What do they tell us about the process of evolution?

Solution:

The remains of organisms that once existed on earth are called fossils. They tell us about the development of simple structured organisms to complex structured organisms. They also give insights into how evolution could have taken place in an organism to sustain themselves in a competitive environment.

Question: 16

Why are human beings who look so different from each other in terms of size, colour and looks said to belong to the same species?

Solution:

A species is a group of organisms that are capable of interbreeding to produce a fertile offspring. In spite of wide differences in size, colour and looks, human beings can interbreed. Hence, all of them are considered as one species.

Question: 17

In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design? Why or why not?

Solution:

Evolution cannot always be equated with progress or better body designs. It does not mean that simple body designs are inefficient. When we take complexity as a criterion, the chimpanzee is better than other given organisms. On the other hand, if we take the ability of survival in almost all kinds of habitat as a criterion, bacteria, having a simple body design, are still the most cosmopolitan organisms found on earth. 

Therefore, bacteria, spiders, fish and chimpanzees are all different branches of evolution.

Questions

Q1	What is heredity?

Q2	What are chromosomes?

Q3	What is evolution?

Q4	What is variation among a species?

Q5	Define asexual reproduction.

Q6	Define sexual reproduction.

Q7	Why is the role of father important in determining the sex of a new born?

Q8	Why is an archaeopteryx considered to be a connecting link between reptiles and birds?

Q9	Why are the wings of an insect and a bird considered as analogous organs?

Q10	Explain why an acquired character cannot be passed on to the next generation.

Q11	Define the terms: (a) Phenotype (b) Genotype

Q12	Differentiate between acquired traits and inherited traits?

Q13	What are the two methods to find the age of fossils?

Q14	Why do homologous structures always have a common ancestor?

Q15	Explain the evolution of wild cabbage done by artificial selection.

Q16	Justify with an example, how genes control characteristics, or traits.

Q17	How are fossils formed?

Q18	Why is the evolution of molecular structure considered highly stable?

Q19	Explain the evolution of eyes.

Q20

How is the sex determination done in humans?

Q1 What is heredity? A1 The inheritance of genetically based characteristics from one generation to another generation is called heredity. Q2 What are chromosomes? A2 Chromosomes are the thread-like structures present in the nucleus of a cell that contain hereditary information of the cell. They are made up of proteins and DNA. Q3 What is evolution? A3 The sequence of gradual changes which result in the formation of new species from primitive organisms over a million of years is called evolution. Q4 What is variation among a species? A4 Parents give birth to offspring which are not exactly like their parents. This is due to changes in the DNA that is being inherited. This is called variation. Q5 Define asexual reproduction. A5 The type of reproduction in which single parent is involved in producing very closely resembling clone-like offspring, thereby resulting in offspring with minor variations, is known as asexual reproduction. Q6 Define sexual reproduction. A6 A mode of reproduction which involves fusion of male gametes with the female gametes to form a new cell called zygote. The zygotes grow into a new organism in due course of time. Sexually reproducing organisms produce offspring with marked, significant and visible variations. Q7 Why is the role of father important in determining the sex of a new born? A7 A male has one X chromosome and one Y chromosome. A female has two X chromosomes. The sex of a child depends on what she/he inherits from the father; X chromosome or Y chromosome. He/she always inherits an X chromosome from his/her mother. Therefore, a girl child is born when she inherits an X chromosome from her father and a boy is born when he inherits a Y chromosome from his father. Q8 Why is an archaeopteryx considered to be a connecting link between reptiles and birds? A8 Archaeopteryx had feathered wings like the birds but teeth and tail like the reptiles. That is why an archaeopteryx is considered to be a connecting link between reptiles and birds. Q9 Why are the wings of an insect and a bird considered as analogous organs? A9 The wings of a bird and insect have different structures. The insects have a fold of membranes as wings which are associated with a few muscles. The wings of a bird is supported by skeleton, flesh and feathers.So even though the wings of  a bird and insect look similar and peform similar function, they have different structures.Thus they are analogous organs. Q10 Explain why an acquired character cannot be passed on to the next generation. A10 Acquired characters e.g., obese body, strong muscles etc. are acquired in response to the environment. These do not impact the reproductive cells of the parent. These characters are not transferred to the next generation as only those characters are transferred to the next generations which are due to the changes in the reproductive cell of an organism. Q11  Define the terms: (a) Phenotype (b) Genotype   A11 Phenotype: The characteristic of an organism which is visible is called phenotype. Example: Expression of morphological characters such as tall or dwarf plant, violet or white flower etc. Genotype: The description of genes present in an organism is called genotype. Q12 Differentiate between acquired traits and inherited traits? A12 Acquired Traits Inherited Traits Acquired traits cannot be passed on to their future generation. Inherited traits can be passed on to their future generation. Acquired traits are due to changes in the non-reproductive cells of an organism. Inherited  traits are due to the changes in the reproductive cells of an organism. Examples: Loss in weight, Strong muscles etc. Examples:  Shape of an organism, colour of the skin etc. Q13 What are the two methods to find the age of fossils? A13 There are two methods to find the age of fossils. They are: Relative method: If we dig into the earth and start finding fossils, it is reasonable to suppose that the fossils we find closer to the surface are more recent ones than the fossils we find in deeper layers. Radio activity: All living objects contain some carbon-14 atoms which are radioactive. When a living organism dies and becomes a fossil, it’s carbon-14 radioactivity gradually decreases. Comparing the carbon-14 radioactivity present in the fossil, with the carbon-14 radio activity present in living organisms today, the age of the fossil can be determined. Q14 Why do homologous structures always have a common ancestor? A14 Structures that have a common basic structure but perform different functions are called homologous structures. Example:  forelimbs of reptiles, amphibians and mammals etc. It is very clear that due to variations in response to the environmental changes, the structures that were once the same have evolved into different shapes. This suggests that all homologous structures have a common ancestor but are variously modified to carry out different activities. Q15 Explain the evolution of wild cabbage done by artificial selection. A15 Humans have cultivated wild cabbage as a food plant foover thousand years. From the same stock of wild cabbage, through the method of artificial selection, they have produced different looking vegetables like cabbage, broccoli, cauliflower, kohlrabi and kale. Cabbage: When some farmers wanted to select for very short distances between leaves, they bred the cabbage we eat. Broccoli: Framers who wanted to select for arrested flower development bred broccoli, Cauliflower: Framers who wanted sterile flowers cultivated cauliflower. Kohlrabi: Farmers who selected swollen parts came up with kohlrabi. Kale: Farmers who simply looked for slightly larger leaves bred a leafy vegetable called kale. Justify with an example, how genes control characteristics, or traits. A16 Characteristics in plants and animals are transmitted to their offspring through genes present in the chromosomes because of sexual reproduction. For each characteristic, both parents possess a pair of genes: one dominant and the other recessive. One parent transfers one of the two genes for each characteristic to the offspring through the gametes. Thus, two genes for each characteristics are received; one through the male gamete and the other through the female gamete. Though the progeny inherits two genes, yet only one of the two inherited gene is dominant and accordingly the progeny shows the dominant trait. Example: A mother has black hair and the father has pale yellow hair. The genotype for the black hair can be written as HH or Hh. The genotype for the pale yellow hair can be written as hh. Now a child in such a case will have either Hh or hh for her hair. If the child has Hh for her hair, the colour of the hair will be black as black is dominant in this combination; otherwise it would be pale yellow. Q17 How are fossils formed? A17 The remains of the dead animals or plants that lived in remote past are called fossils. Generally, the dead bodies of living organisms get decomposed and are lost over a period of time. In certain situation, the body as a whole or a part of it remains in an environment that does not let it decompose completely. Such parts remain inside the earth for a long period of time and are obtained as fossil by digging the earth. Example:  Formation of leaf fossil. (a) A dead leaf may be caught in a mud. (b) The mud will not let the leaf decompose quickly. (c) The mud will harden over a period and will set around the leaf.       The mud retains the impression of the body parts of the leaf. This forms fossil leaf.   Q18 Why is the evolution of molecular structure considered highly stable? A18 We see immense diversity in size, form, structure and morphological features in the living world. But at the molecular level these, diverse types of organisms exhibit unbelievable similarity. For instance, the basic biomolecules like DNA, RNA, carbohydrates, proteins etc. exhibit remarkable similarity in all organisms. Q19 Explain the evolution of eyes. A19 An eye is a complex organ. Such a complex organ have been created bit-by-bit over generations. First the basic eye as is seen in flatworm developed. The eyes of flatworm can detect light. Starting from a simple eye, more and more complex form of eyes have evolved in various organisms. Insects, an octopus, vertebrates etc. all have eyes. The structure of the eye in each of these organisms is different. This proves that the eye in each organism has a separate evolutionary origin. Q20 How is the sex determination done in humans? A20 Sex determination of a human offspring is a mechanism which determines the individual to be a male or a female based on the sex chromosomes present in it. Human cells contain 23 pairs of chromosomes, out of which the 23rd pair is composed of sex chromosomes which are named as X and Y chromosomes. These are inherited one from each of the parents. The 23rd pair contains one X and one Y chromosome in a male. The 23rd pair in a female contains two X chromosomes. This means that all the eggs would have X chromosome as the 23rd chromosome, while a sperm may have either X or Y chromosome. When a sperm with X chromosome fertilizes the egg, the resulting zygote develops into a female child. When a sperm with Y chromosome fertilizes the egg, the resulting zygote develops into a male child.