"AKC SCIENCE CLASSES"
CLASS 10 TH (CBSE AND MP BOARD)
CHAPTER 09
HEREDITY AND EVOLUTION
INTEXT QUESTIONS AND ANSWERS
NCERT INTEXT QUESTIONS (PAGE NO. 143)
Q.01:- 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?
Ans:- Trait B as it is present in more members of the population. It must have arisen earlier and has now spread to 60% of the population. Whereas trait A is new and has spread to only 10% of the population.
Q.02:- How does the creation of variations in a species promote survival?
Ans:- Reproduction processes, especially sexual reproduction, give rise to new individuals that are similar, but subtly different. Thus, different variants emerge in a species. The variants which are suitable to prevailing environment survive by natural selection. Rest of members of a species may vanish.
Environment also goes on changing. Now, individuals (variants) which are suitable to the changed environment will survive. Thus continuity of the species will be maintained.
For example, Bacteria variants which can withstand tolerate heat will survive better in a heat wave than variant which cannot heat wave. It proves that creation of variations in a species promote survival.
NCERT INTEXT QUESTIONS (PAGE NO. 147)
Q.01:- How do Mendel's experiments show that traits may be dominant or recessive?
Ans:- The trait which is expressed in 75% individuals in F2 generation after self-fertilisation is dominant. The trait which appears in 25% individual is recessive.
Q.02:- How do Mendel's experiments show that traits are inherited independently?
Ans:- Mendel took two pairs of alternative expression of two traits of a 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 exist in the parents. This indicates that pair of alternate characteristics behave independently of the other pair and are thus inherited independent of each other. (As depicted at Pt. 06 of basic concepts).
Q.03:- 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?
Ans:- (i) If A is considered to be dominant over O then the following combinations are possible :-
Male :- AO and Female :- OO
Daughter can be OO and hence have blood group O.
(ii) If O is considered to be dominant over A then the following combinations are possible :-
Male :- AA and Female :- OO or OA
Thus from the information given in the question we cannot ascertain which blood group is dominant.
Q.04:- How is the sex of the child determined in human beings?
Ans:- In human, 23 pairs (46) chromosomes are present out of these 22 pairs have a maternal and paternal copy. These chromosomes (autosomes) determine the characters other than sex. The 23rd pair of chromosomes are called sex chromosomes. Women have perfect pair of sex chromosomes, both called XX chromosomes. Men have a mismatched pair of chromosomes-one is a normal size X chromosome and a short one called Y chromosome. So, women have XX chromosomes and men have XY sex chromosomes.
All children will inherit from their mother regardless of whether they are boys or girls. It means that the sex of the children will be determined by what sex chromosomes they inherit from their father. A child who inherits an X chromosomes from father will be girl, and one who inherits a Y chromosome from father will be a boy.
NCERT INTEXT QUESTIONS (PAGE NO. 150)
Q.01:- 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 the 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.02:- Why are traits acquired during the life-time of an individual not inherited?
Ans:- The traits acquired during the life-time are changes in the non-reproductive cells of the organism and are not capable of being passed on to next generation. Changes that occur in DNA of germ cells are only inherited.
Q.03:- Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
Ans:- The tigers have very less variation in genetic characteristics among each other and if the natural conditions would change drastically no tiger may survive. For example, if a deadly diseases was to infect the tigers, all the tigers may die from it as there would be less variation in the genotype of survive the disease. Decrease in population of tigers also indicates that tiger variants are not adapted the existing environment and may extinct soon.
NCERT INTEXT QUESTIONS (PAGE NO. 151)
Q.01:- What factors could lead to the rise of a new species?
Ans:- Accumulated variations favourable to the natural environment; geographical isolation of a population; action of different environmental factors on these isolated populations; and reproductive isolation and change of number of chromosomes result in the formation of new species.
Q.02:- Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?
Ans:- No, as the population is self-pollinating it would be less prone to factors which result from geographical isolation. Conversely, in a cross-pollinated species geographical isolation would be a major factor as it would result in faster accumulation of variations (genetic drift) in the two geographically separated populations.
Q.03:- Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
Ans:- No, asexually reproducing organisms have very little variation over generations. Any change resulting from geographical isolation may not be passed on to the next generation. As these variations in DNA are not enough to raise a new species.
NCERT INTEXT QUESTIONS (PAGE NO. 156)
Q.01:- Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Ans:- Structure of forelimb in a frog, lizard, bird and horse is similar with similar bones which are modified to suit the function they perform. From this it can be safely assumed that they may have evolved from a common ancestor.
Another way is the study of DNA of relevant species.
Q.02:- Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not?
Ans:- The wing of a butterfly and wing of a bat are used for the same function of flying. However, the wings of a butterfly is structurally very different from wing of bat which has bones and skin. Thus they are not homologous organs.
Q.03:- What are fossils? What do they tell us about the process of evolution?
Ans:- Fossils are any impression or imprint left by some previous organism in the soft mud which subsequently hardened or the moulds and casts of entire organisms which become preserved. Fossils tell about the organisms that lived long ago. They tell about the structure of such organisms and the time period during which they lived. The fossils found in upper strata of rocks are considered to be newer than those found in the lower strata. It is also seen from the fossils that the organisms become more complex in the upper strata when compared to the lower strata which indicates towards the evolutionary process. Also transitional fossils like Archaeopteryx are known which were intermediaries between reptiles and birds.
NCERT INTEXT QUESTIONS (PAGE NO. 156)
Q.01:- Why are human beings who look so different from each other in terms of size, color and looks said to belong to the same species?
Ans:- This is because although the genetic makeup of humans may be slightly different in different races of people, there is no reproductive isolation. Reproductive isolation differentiates one species from the other. Human beings different in size, color and looks can marry among themselves and produce fertile offspring.
Q.02:- In evolutionary terms, can be say which among bacteria, spiders, fish and chimpanzees have a 'better' body design? Why or why not?
Ans:- There is no real progress in the idea of evolution. In terms of evolution, evolution causes generation of diversity and the shapping of the diversity by environmental selection. Due to evolution more and more complex body designs have emerged over time. It does not mean older and simpler body designs are inefficient and complex body designs like spiders, fish and chimpanzees have better body design.
For example, bacteria are oldest and have simpler body design still survive. They are found in the most inhospitable habitats like hot springs, deep sea, the ice in Antarctica. So, bacteria, species in the teeming spectrum of evolving life. Thus, all the organisms which exist have a body design which is 'better' as it suited to their environment.
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