Class 10 Science Chapter 9 Heredity and Evolution

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Class 10 Science Chapter 9 Heredity and Evolution

Also, you can read the CBSE book online in these sections Solutions by Expert Teachers as per NCERT (CBSE) Book guidelines. These solutions are part of SEBA All Subject Solutions. Here we have given Assam BoardClass 10 Science Chapter 9 Heredity and Evolution Solutions for All Subjects, You can practice these here.

Heredity and Evolution

Chapter – 9

GENERAL SCIENCE

Textual Questions and Answers:

 Page – 143 

Q.1. If a trait A exist 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? 

Ans: In asexual reproduction, the reproducing cells produce a copy of their DNA through some chemical reactions. However, this copying of DNA is not accurate and therefore, the newly formed DNA has some variations.

It can be easily observed in the above figure that in asexual reproduction, very few variations are allowed. Therefore, if a trait is present in only 10% of the population, it is more likely that the trait has arisen recently. Hence, it can  be concluded that trait B that exists in 60% of the same population has arisen earlier than trait A. 

Q.2. How does the creation of variations in a species promote its survival? 

Ans: Genetic variations enable the species to better adapt to changes in its environment. Moreover, it is an important force in evolution as it allows the frequency of alleles to increase or decrease through natural selection. These variations will determine the difference between extinction or continuation of the species.

Page – 147 

Q.1. How do Mendel’s experiments show that traits may be dominant or receive? 

Ans: Mendel’s experiments show that the Traits may be dominant or recessive by performing a monohybrid cross. Monohybrid cross between two pure breeding varieties always obtained hybrid progeny exhibiting one parental trait while the opposite trait was never expressed in the F1 generation. It suggested that two alleles of a gene are often either dominant or recessive and the presence of the dominant allele in F1 hybrids masks the expression of the recessive one.

Q.2. How do Mendel’s experiments show that traits are inherited independently? 

Ans: Mendel carried out dihybrid crosses by crossing two pea plants differing in contrasting traits of two characters. For example, he crossed a pea plant having yellow colour and round seed characters with another pea plant bearing green colour and wrinkled seed characters. In the F2 generation, he obtained pea plants with two parental and two recombinant phenotypes as yellow round and green wrinkled (parental) and yellow wrinkled and green round (recombinant). This indicated that traits separated from their original parental combinations and got inherited independently.

Q.3. A man with blood group A marries a women with the 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? 

Ans: No. This information is not sufficient to determine which of the traits – blood group A or O – is dominant. Thus is because we do not know about the blood group of all the progent. Blood group A can be genotypically AA of AO. Hence, the information is incomplete to draw any such conclusion.

Q.4. How is the sex of the child determined in human beings? 

Ans: Sex of a child depends on the chromosome in the gamete of the father. The unfertilized egg has one X chromosome. The sperm either has X chromosome or Y chromosome. If sperm carrying Y chromosome fertilizes with the egg, male child will be born with the genetic constitution XY. But if sperm carrying X chromosome fertilized with the egg, female child will be born with the genetic constitution XX. 

Page – 150

Q.1. What are the different ways in which individuals with a particular trait may increase in a population? 

Ans: An individual trait may increase in a population in the following ways:

1. Natural Selection: If a trait is useful to the population, it will increase naturally. It may directly lead to the evolution of species populations by adaptations to fit their environment better. That particular trait may thus increase in the population.

2. Genetic drift: If a population faces an accident such that the majority of its members get killed, the remaining members will pass on their traits to the subsequent generations. This leads to an increase of the trait in the population. This is the notion of genetic drift, which provides diversity without any adaptation.

3. Geographic isolation: Where a population of species gets separated by their respective group due to physical/natural barriers.

4. Mutation: Slight changes in the genetic information of the offspring during fertilization.

5. The trait is beneficial to the population: If a trait is beneficial to a population, it will increase naturally. Such green color in beetles is favorable as it helps them in camouflage against predators.

Q.2. Why are traits acquired during the life – time of an individual not inherited? 

Ans: For a trait of an organism to be inherited, it should being about a change in the genes present in the reproductive cells or gametes of that organism . The traits acquired during the life time of a person do not bring about a change in the genes present in its reproductive cells or gametes and hence they are not inherited by the offsprings. 

Q.3. Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics? 

Ans: A small number of surviving tiger are a cause of worry from the point of genetics because these tigers carry the genes which have made them adapt to the particular environment during the long process of evolution. If these tigers become extinct by some diseases or by hunting then the genes responsible for survival would also become extinct and would not be able to contribute in the survival of future generations.

Page – 151 

Q.1. What factors could lead to the rise of a new species? 

Ans: The main factors which lead to the rise of new species are natural selection, genetic drift, geographical isolation, and mutation. In speciation, a single evolutionary lineage gets split into two or more genetically independent lineages due to the actions of several environmental factors.

EXERCISES 

Q.1. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing with 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 for can be depicted as –

(a) TTWW 

(b) TTww 

(c) TtWW 

(d) TtWw 

Ans: (c) TtWW. 

Q.2. An example of homologous organs is 

(a) Our arm and a dog’s fore – leg. 

(b) Our teeth and an elephant’s tasks.

(c) Potato and runners of grass.

(d) All of the above.

Ans: (d) All of the above.

Q.3. In evolutionary terms, we have more in common with 

(a) A chinese school – boy 

(b) A chimpanzee.

(c) A spider.

(d) A bacterium. 

Ans: (a)  A chinese school – boy.

Q.4. A study found that children with light – coloured eyes are likely to have parents with light – coloured eyes. On who this basis can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not? 

Ans: No because we cannot say with certainty whether light eye colour is dominant or recessive. However, since both children and their parents have light eye colour, the possibility that light eye colour is recessive trait.

Q.5. How are the areas of study – evolution and classification interlinked? 

Ans: Classification and evolution are highly interlinked fields of study. Classification is influenced by evolution. The modern system of classification is also called phylogenetic classification; which means it is based on evolutionary relationships. Hence, evolution and classification are closely related.

Q.6. Explain the terms analogous and homologous organs with examples. 

Ans: Homologous organs are those organs which have the same basic structural design and origin but have different functions.

For example: the forelimbs of humans and the wings of birds look different externally (morphologically dissimilar) but their skeletal structure is similar.

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

For example: the wings of birds and insects.

Q.7. Outline a project which aims to find the dominant coat colour in dogs. 

Ans: Cross the homozygous male BB and homozygous female bb, and then observe the coat colour in dog progeny (offspring). If all progeny have black colour, this means that black colour will be the dominant coat colour in dogs and if progeny will have brown colour then the brown colour will be dominant coat colour.

Q.8. Explain the importance of fossils in deciding evolutionary relationship.

Ans: Fossil provide us evidence about:

(i) The organisms that lived long ago such as the time period during which they lived, their structure etc.

(ii) Evolutionary development of species i.e., line of their development.

(iii) Connecting links between two groups. For example, feathers present in some dinosaurs means that birds are very closely related to reptiles.

(iv) Which organisms evolved earlier and which later.

(v) Development of complex body designs from the simple body designs.

Q.9. What evidence do we have for the origin of life from inanimate malter? 

Ans: Miller-Urey experiment provided evidence for the origin of life from inanimate matter. In the experiment, they created an atmosphere containing molecules like ammonia, methane and hydrogen sulphide, but no oxygen. This atmosphere was similar to the atmosphere present during the primitive Earth. Temperature was maintained constant at 100°C and sparks were passed through the mixture to stimulate lightning. After a particular time, certain amount of the carbon from methane had been converted to simple compounds of carbon like amino acids. Amino acids are the precursors of the proteins and proteins are the molecules that support the life in basic form.

Q.10. Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that al thom reproduce sexually? 

Ans: 

1. In asexual reproduction, there is no fusion of gametes, and only 1 parent is involved. So the only reason for variation is errors during DNA copying.
2. These variations are very minute and can only be seen over a long period of time since too much deviation can lead to unsurvivable alterations in the genetic makeup for the progeny.
3. Sexual reproduction gives rise to more viable variations than asexual reproduction because 2 gametes from different individuals combine to produce an organism. 
4. It involves 2 parents so the offspring (child) shows variation due to the presence of characteristics of both parents.
5. These variations help adapt to the environment in a better, more efficient manner , and result in evolution and formation of new species over time .

Q.11. How is the equal genetic contribution of male and female parents ensured in the progeny? 

Ans: There are 23 pairs of chromosomes. Most human chromosomes have material and a paternal copy. We have 22 such pairs. These pairs contain half chromosomes from mother and half from father. One pair is called sex chromosomes. At the time of sex determination, the egg cell fuses with the sperm cell which are haploid to form zygote. Zygote is diploid which contains 23 chromosomes from mother and 23 from father. In this way, an equal genetic contribution of male and female parents is ensured in the progeny.

Q.12. Only variation that confer advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not? 

Ans: It is agreeable that only variations that confer an advantage to an individual organism will survive in a population. All variation does not necessarily provide an equal chance of survival to an organism in the environment. Survival chances highly depend on the nature of variations. For example- variation leading to the increase of heat-resistant bacteria is beneficial to the bacteria for its survival when it finds itself in a condition where suddenly there is an increase in the temperature of its habitat above the optimum temperature required for survival.