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Class 10 Heredity and Evolution Short answers

Chapter 9: Heredity and Evolution

Short Answer Type Questions – I [2 Marks]

Q.1. Why did Mendel choose pea plant for his experiments?

Ans. Mendel chose the pea plant for his experiments due to the following reasons :

(a) Easy to grow. (b) Short life span.

(c) Easily distinguishable characters. (d) The larger size of the flower.

(e) Self-pollinated

Q.2. (i) What is the unit of inheritance in a living organism?

(ii) Where are they located?

Ans. (i) Genes

(ii) Genes are located on the chromosomes.

Q.3. Why is the progeny always tall when a tall pea plant is crossed with a short pea plant?

Ans. When a tall (TT) pea plant is crossed with a short (tt) pea plant, the progeny is always tall. It is because the gametes from two plants combine to form a tall plant (Tt) with one dominant and one recessive gene. Tallness (T) is dominant over the shortness (t) characteristic. Thus, resultant plants are always tall.

Q.4. Give the law of segregation.

Ans. According to the law of segregation, during gamete formation, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene.

Q.5. List two differences in tabular form between dominant trait and recessive traits.


Q.6. Why offsprings differ from parents in certain characters?

Ans. It is due to biparental percentage. The genes on chromosomes which pass over to the next generation are partly derived from both the parents (mother and father). During fertilisation of an egg by the sperm, a new combination of chromosomes enters the zygote, due to which certain variations occur in the offspring. Thus, brothers and sisters show variations in their complexion, habits, behaviour and other characters.

Short Answer Questions – I [2 Marks]

Q.1. Name two homologous structures in vertebrates. Why are they so-called?

Ans. Two homologous structures invertebrates are :

(i) limbs of birds and reptiles

(ii) limbs of reptiles and amphibians

These are so-called because these organs have similar structures to perform different functions.

Q.2. Does geographical isolation gradually lead to speciation? Give a suitable example.

Ans. Yes, geographical isolation gradually leads to speciation. Geographical isolation may impose limitations to sexual reproduction of the isolated population. Slowly, isolated individuals will reproduce among themselves and generate new variations. Continuous accumulation of those new variations through a few generations may ultimately lead to the formation of a new species.

Q.3. Mention three important features of fossils which help in the study of evolution.

Ans. (i) Fossils represent modes of preservation of ancient species.

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

(iii) Fossils help in establishing the time period in which organisms lived.

Q.4. “Birds have evolved from reptiles”. State evidence to prove the statement.

Ans. Fossils of certain dinosaurs and reptiles show imprints of feathers along with their bones but they could not fly presumably. However, they used feathers for insulation only. Later, they evolved and adapted feathers for flight, thus becoming the ancestors of present-day birds.

Q.5. What is DNA copying? State its importance.

Ans. DNA copying is a process where a DNA molecule produces two similar copies of itself in a reproducing cell.

Importance of DNA copying :

(i) It makes the transmission of characters from parents to the next generation possible.

(ii) It causes variation in the population.

Q.6. ‘Variations that confer an advantage to an individual organism will survive in a population.’ Justify. Ans. Useful variations give advantage to individuals in obtaining more food, reproduction, adaptation to environmental changes and higher success in the struggle for existence. They give benefit in survival, thus increasing the population. Differential reproduction increases the useful variations in the populations. Other individuals with harmful variations will be destroyed. For example, some bacteria have the ability to tolerate high temperature. But other non-resistant bacteria will be killed in the presence of high temperature.

Short Answer Type Questions – I [2 Marks]

Q.1. Give some tools with the help of which human evolution was studied.

Ans. Human evolution was studied by

(i) studying fossils

(ii) determining DNA sequences

(iii) time-dating.

Q.2. What does the study of human evolution indicates regarding the different races of humans?

Ans. Study of human evolution indicates that all the races of Homo sapiens belong to a single species which evolved in Africa and spread acorss the world in stages.