CBSE Class 10 Biology Heredity And Evolution Worksheet Set C

Heredity and Evolution

Question : A study found that children with light-coloured eyes are likely to have parents with lightcoloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?
Answer: Let us assume that children with light-coloured eyes can either have LL or Ll or ll genotype. If the children have LL genotype, then their parents will also be of LL
genotype.
                   LL × LL
                       ↓
                      LL
If the children with light-coloured eyes have ll genotype, then their parents will also have ll genotype.
                   ll × ll
                      ↓
                      ll
Therefore, it cannot be concluded whether light eye colour is dominant or recessive.

Question : In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design? Why or why not?
Answer: Evolution cannot always be equated with progress or better body designs. Evolution simply creates more complex body designs. However, this does not mean that the simple
body designs are inefficient. In fact, bacteria having a simple body design are still the most cosmopolitan organisms found on earth. They can survive hot springs, deep sea,
and even freezing environment.Therefore, bacteria, spiders, fish, and chimpanzees are all different branches of evolution.

For example, in a family, a brother and sister are closely related and they have a recent common ancestor i.e., their parents. A brother and his cousin are also related but less than the sister and her brother. This is because the brother and his cousin have a common ancestor i.e., their grandparents in the second generation whereas the parents were from the first generation. With subsequent generations, the variations make organisms more different than their ancestors.
This discussion clearly proves that we classify organisms according to their resemblance which is similar to creating an evolutionary tree.

Question : Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?
Answer: Geographical isolation can prevent the transfer of pollens among different plants. However, since the plants are self-pollinating, which means that the pollens are transferred from the anther of one flower to the stigma of the same flower or of another flower of the same plant, geographical isolation cannot prevent speciation in this case.

Question : 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?
Answer: In sexual reproduction, two individuals having different variations combine their DNA to give rise to a new individual. Therefore, sexual reproduction allows more variations,

whereas in asexual reproduction, chance variations can only occur when the copying of DNA is not accurate.Additionally, asexual reproduction allows very less variations because if there are more variations, then the resultant DNA will not be able to survive inside the inherited cellular apparatus.

However, in sexual reproduction, more variations are allowed and the resultant DNA is also able to survive, thus making the variations viable.
Variation and Evolution: Variants help the species to survive in all the conditions.Environmental conditions such as heat, light, pests, and food availability can change suddenly at only one place. At that time, only those variants resistant to these conditions would be able to survive. This will slowly lead to the evolution of a better adapted species. Thus, variation helps in the evolution of sexually reproducing organisms.

Question : How does the creation of variations in a species promote survival?
Answer: Sometimes for a species, the environmental conditions change so drastically that their survival becomes difficult. For example, if the temperature of water increases suddenly, most of the bacteria living in that water would die. Only few variants resistant to heat would be able to survive. If these variants were not there, then the entire species of bacteria would have been destroyed. Thus, these variants help in the survival of the species.
However, not all variations are useful. Therefore, these are not necessarily beneficial for the individual organisms.

Question : 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
Answer:
(c) The genetic make-up of the tall parent can be depicted as TtWW Since all the progeny bore violet flowers, it means that the tall plant having violet flowers has WW genotype for violet flower colour. Since the progeny is both tall and short, the parent plant was not a pure tall plant. Its genotype must be Tt.
Therefore, the cross involved in the given question is
       TtWw × ttww
                ↓
       TtWw − ttww
Therefore, half the progeny is tall, but all of them have violet flowers.

Question : What are the different ways in which individuals with a particular trait may increase in a population?
Answer:Individuals with a particular trait may increase in a population as a result of the following:
(i) Natural selection: When that trait offers some survival advantage.
(ii) Genetic drift: When some genes governing that trait become common in a population.
(iii) When that trait gets acquired during the individual’s lifetime.

More Question

1) Give examples of animals where sex determination is not genetically determined?

2) 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?

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

4) What do fossils tell us about the process of evolution?

5) Why did Mendel choose garden pea for his experiments

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

7) What is speciation?

8) How can we say that a child has two versions of a trait?

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

10) The genotype of purple flowered pea plants is denoted as WW and that of white flowered pea plant as ww. When these two are crossed

  i) What color of flowers do you expect in their F1 progeny?

  ii) What will be the percentage of white flowered plants produced if F1 plants are self pollinated?

Students must free download and practice these worksheets to gain more marks in exams. CBSE Class 10 Biology Heredity And Evolution Worksheet Set C