Class 10 Science Chapter 9 Heredity and Evolution

Class 10 Science Chapter 9 Heredity and Evolution The answer to each chapter is provided in the list so that you can easily browse throughout different chapters NCERT Class 10 Science Chapter 9 Heredity and Evolution and select need one.

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Class 10 Science Chapter 9 Heredity and Evolution

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

Heredity and Evolution

Chapter – 9



 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 :- The trait B which exists in 60% of the population is likely to have arisen earlien . This is because the traits produced in an organism during successive generations get accumulated in the populations of the species . 

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

Ans :- The creation of variations to a species is that it increases the changes of its survival in a changing environment . For example the accumulation of ‘ heat resistant ‘ variation in some bacteria will ensure its survival even when the temperature in its environment rises too much due to a heat wave or some other reasons . On the other hand , the bacteria which did not have this variation to with stand heat would not survive under these circumstances and dic . 

Page -147 

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

Ans :- The trait which expressed in 75% individuals in F₂ generation after self fertilisation is dominant . The trait which appears in 25% individuals is recessive.

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

Ans :- Mendal took two pairs of alternative expression of two traits of pea plant and crossed them . The F₁ progeny showed only the dominant characteristics among each pair . The F₂ progeny had phenotypes similar to parents but also new phenotypes that did not exists in the parents . This indicates that pair of alternate characteristics behave independently of the other pair and are thus inherited independent of each other . 

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 enough to tell us which of the traith , blood group A or blood group O , is dominant . This is because : 

( i ) If the blood group A is dominant trait and blood group O is recessive trait , the daughter can have blood group O.

( ii ) and even if the blood group A is recessive trait but blood group O is dominant trait , the daughter can still have blood group O.

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

Ans :- The chromosomes which determine the sex of a person are called sex chromosomes . There are two types of sex chromosomes one is called X chromosome and the other is called Y chromosome . 

( i ) A male has one X chromosome and one Y chromosome . This means that half the male gametes or half the sperms will have X chromosomes and the other half will have Y chromosomes .

( ii ) A female has two X chromosomes but no Y chromosomes . This means that all the female gametes called ova will have only X chromosomes . 

The sex of child depends on what happens at fertilisation : 

( a ) If a sperm carrying Y chromosome fertilises an ovum which carries X chromosome , then the child born will be a boy ” This is because the child will have XY combination of sex chromosomes . 

Page -150

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

Ans :- If a variation occurs in a population and that variation results in better survival of the organism in the prevailing natural conditions , then the trait would be selected naturally and more individuals with that trait would survive in the population . 

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 :- The tiger have very less variation in genetic characteristics among each other and if the natural conditions would charge drastically no tiger may survive. 

Page -151 

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

Ans :- Geographical isolation of a population caused by various types of barriers . The geographical isolation leads to reproductive isolation


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 :- As the trait is expressed in all the children of such parents , the parents are homozygous for light eye colour . However , it cannot be concluded whether the light eye colour is dominant or recessive . 

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

Ans :- The more characteristics two organisms have in common , the more closely they are related . And the more closely they are the evolutionary chain.sto related , the more recently they will have had a common ancestor in evolutionary chain.

The more different characteristics two organisms have , the more remotely they are related . And the more remotely they are related , they will have had a common ancestor in the more remote past . 

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

Ans :- Analogous organs :- Those organs which have different basic structure or different basic design but have similar appearance and perform similar functions are called analogous organs . 

For example : – The wings of an insect and a bird have different structures but they perform the same function of flying.

Homologous organs :- Those organs which have the same basic structure or same basic design but different functions are called homologous organs . For examples the forelimbs of a man , a lizard , a frog , a bird and a bat seem to be built from the same basic design of bones but they perform different functions . 

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

Ans :- A black homozygous male is mated with a white homozygous female . If the progeny has all black dogs then the dominant coat colour is black .

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

Ans :- The importance of fossils in deciding evolutionary relationship is that they provide evidence that the present animals and plants have originated from the previously existing animals and plants through the process of continuous evolution . 

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

Ans :- Miler and Urey conducted an experiment in 1953 in which they assembled the inorganic gases , known to be prevalent in early earth and maintained the temperature at 100° C and passed sparks over the mixture of gases . At the end of a week , 15% of the carbon was converted to simple compounds of carbon including amino acids which are the building blocks of proteins . This shows that complex organic molecules can arise from simple inorganic molecules under certain conditions which prevailed during the early period in earth’s life . These complex molecules are building blocks of cells and they can give rise to a living organism capable of self duplication . 

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 :- The asexual reproduction gives rise to small variations because in this process the DNA of only one parent is copied . Due to this , the offsprings produced look almost the same . On the other hand sexual reproduction gives rise to large variations because in this process DNA from the gametes of two parents in combined together . 

The large genetic variations produced during sexual reproduction lead to the continuous evolution of those organisms which reproduce sexually . In fact , sexual reproduction plays an important role in the origin of new species having different characteristics . All this is not possible in the case of asexual reproduction . 

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

Ans :- The equal genetic contribution of male and female parents in a progeny is ensured through the special type of reproductive cells which have only half the amount of DNA as compared to other body cells . So when the gametes from male and female parent combine during sexual reproduction to form a fertilised egg called zygote , they contribute equal amount of DNA.

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 :- Variations which confer an advantage to an individual organism may or may not survive in the population depending upon the social behaviour of the organism . A in a population while a variation in an animal like a leopard may survive . 

Additional Questions and Answers

Q.1. What is called heredity ? 

Ans :- The transmission of characters or traits from the parents to their offsprings is called heredity . 

Q.2. What do you mean by variation . Give example . 

Ans :- The differences in the characters or traits among the individuals of a species is called variation . For example , human height is a trait which shows variation . This is because some people are very tall , some are less tall , some have medium height , some have short height whereas others are very short . 

Q.3. What is gene ? 

Ans :- A gene is a unit of DNA on a chromosome which governs the synthesis of one protein that controls a specific characteristic of an organism.

Q.4. Define :- ( a ) Dominant gene.

                       ( b ) recessive gene. 

Ans :- ( a ) Dominant gene :- The gene which decides the appearance of an organism even in the presence of an alternative gene is known as a dominant gene . 

( b ) Recessive gene :- The gene which can decide the appearance of an organism only in the presence of another identical gene is called a recessive gene . 

Q.5. What do you mean by phenotype ? Give example .

Ans :- The characteristic or trait which is visible in an organism is called its phenotype .

For example , being tall ‘ or ‘ short ‘ are phenotypes of a plant because these traits can be seen by us or they are visible to us . 

Q.6. What is hybrid ?

Ans :- A new form of plant resulting from a cross or breeding of different varieties of a plant is known as hybrid.

Q.7. Define Mendel’s first law of inheritance . 

Ans :- According to Mendel’s first law of inheritance : – The characteristics or traits of an organism are determined by internal ‘ factors ‘ which occur in pairs . Only one of a pair of such factors can be present in a singh gamete . 

Q.8. Define Mendel’s second law of inheritance . 

Ans :- According to Mendel’s second law of inheritance:- In the inheritance of more than one pair of traits in a cross simultaneously , the factors responsible for each pair of traits are distributed independently to the gametes . 

Q.9. world Explain an acquired trait with an example . 

Ans :- A trait of an organisms which is not inherited ‘ but develops in response to the environment is called an acquired trait . For example , if a beetle does not get sufficient food for a considerable time , its weight will be reduced due to starvation . The low weight of this beetle is an acquired trait of the beetle which has bee acquired in response to the environment which contained insufficient food.

Q.10. Define evolution . Why it is called organic evolution ? 

Ans :- Evolution is the sequence of gradual changes which take place in the primitive organisms over millions of years in which new species are produced .

Since the evolution is of the living organisms so it is called organic evolution . 

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