Q17 of 30 Page 1

Mention the cause of Down’s syndrome and Turner’s syndrome respectively in humans.

Down’s syndrome is caused due to the presence of the additional copy of the 21st chromosome caused due to nondisjunction, i.e., the failure of separation of the sister chromatids during cell division. Therefore it is also called as the trisomy of 21. It is represented as 47, XX/XY.

Turner’s syndrome is caused due to the absence of one of the X chromosomes in females arising due to nondisjunction of X chromosomes during the ovum formation. It is represented as 45, XO.


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15

Name the technique used in separating the DNA fragments to be used in biotechnology experiments. Write how does the separation of DNA fragments occur.

 16

Write the possible genotypes of the following:

(a) The F1 progeny of a cross between a heterozygous tall pea plant and a dwarf pea plant.


(b) The woman whose son has blood group ‘O’ and her husband has blood group ‘A’.


 18

‘Darwin’s finches are a good example of adaptive radiation.’ Justify.

OR


Identify the examples of analogous organs from the following and name the type of evolution these are the result of:


(a) Eyes of octopus and mammal


(b) Forelimbs of human and cheetah


(c) Thorns of Bougainvillea and tendrils of Cucurbita


(d) Flippers of penguins and dolphins


 19

How do the surgical methods of contraception (sterilisation) prevent contraception? Mention one advantage and one disadvantage of this method.