NCERT Class X Science Solutions: Chapter 9 – Heredity and Evolution Part 1

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Question 1:

A Mend Elian 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

  1. TTWW

  2. TTww

  3. TtWW

  4. TtWw

Answer:

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

Therefore, half the progeny is tall, but all of them have violet flowers.

Question 2:

An example of homologous organs is

  1. Our arm and a dog’s fore-leg.

  2. Our teeth and an elephant’s tusks.

  3. Potato and runners of grass.

  4. All of the above.

Answer:

The organs which are structurally same but functions are different are called homologous organs. All of these are examples of homologous organs.

The arm of a human, the wing of a bird or a bat, the leg of a dog and the flipper of a dolphin or whale are homologous structures. They are different and have a different purpose, but they are similar and share common traits. They are considered homologous structures because they have a similar underlying anatomy.

Question 3:

In evolutionary terms, we have more in common with

  1. A Chinese school-boy.

  2. A chimpanzee.

  3. A spider.

  4. A bacterium.

Answer:

In evolutionary terms, we have more in common with a Chinese school boy.

Chinese school boy is a member of same species that we are of i.e., Homo sapiens. It is the environment that has caused some morphological variations.

Question 4:

A study found that children with light - coloured eyes are likely to have parents with light coloured 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.

If the children with light-colored eyes have ll genotype, then their parents will also have ll genotype.

Therefore, it cannot be concluded whether light eye colour is dominant or recessive.

ations) without any survival advantage.

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