Q9 of 53 Page 33

If a father and son are both defective in red-green colour vision, is it likely that the son inherited the trait from his father? Comment.

Colour blindness is common hereditary condition which means it is passed down from parents. Red/green colour blindness is passed from mother to son on the 23rd chromosome, which is known as the sex chromosome. The faulty gene for colour blindness is found only on the X chromosome.

When the father is colour blind, he can only pass an X chromosome to his daughter. Hence a colour blind boy cant receive a colour blind gene from his father, even if his father is colour blind. A father can only pass Y gene to his son.



Thus its clear that a son can inherit the disease only from his mother even if his father is colour blind. Because only a mother can pass X chromosome to his son.



More from this chapter

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7

In peas, tallness is dominant over dwarfness, and red colour of flowers is dominant over the white colour. When a tall plant bearing red flowers was pollinated with a dwarf plant bearing white flowers, the different phenotypic groups were obtained in the progeny in numbers mentioned against them:

Tall, Red = 138


Tall, White = 132


Dwarf, Red = 136


Dwarf, White = 128


Mention the genotypes of the two parents and of the four offspring types.


 8

Why is the frequency of red-green colour blindness is many times higher in males than that in the females?

 10

Discuss why Drosophila has been used extensively for genetical studies.

 11

How do genes and chromosomes share similarity from the point of view of genetical studies?