question_answer

Directions : (36 - 40)

Read the passage given below and answer the following questions.

Colour blindness is a sex-linked recessive disorder due to defect in either red or green cone of eye resulting in failure to discriminate between red and green colour. This defect is due to mutation in certain genes present in the X-chromosome. It occurs in about 8 percent of males and only about 0.4 percent of females. This is because the genes that lead to red-green colour blindness are on the X-chromosome. Males have only one X-chromosome and females have two. The son of a woman who carries the gene has a 50 percent, chance of being colour blind. The mother is not herself colour blind because the gene is recessive. That means that is effect is suppressed by her matching dominant normal gene. A daughter will not normally be colour blind, unless her mother is a carrier and her father is colour blind. The gene for normal vision is dominant. The normal gene and its recessive allele are carried by X-chromosome. In female colour blindness appears only when both the sex chromosomes carry the recessive gene\[\left( {{X}^{c}}/{{X}^{c}} \right)\]. The females have normal vision but function as carrier if a single recessive gene for colour blindness is present \[\left( X{{X}^{c}} \right)\]. However, in human males the defect appears in the presence of a single recessive gene \[\left( {{X}^{c}}Y \right)\] because Y chromosomes of males do not carry any gene for colour vision. Colour blindness, like any other sex linked trait, shows criss-cross inheritance. Colour- blindness does not mean not seeing any colour at all, it means that those who are colourblind have trouble in seeing the differences between certain colours. Most colourblind people can't tell the difference between red or green. That does not mean that they cannot do their normal work - Infact they can also drive - they learn to respond to the way the traffic signal lights up, the red light is generally on the top and. green is on the bottom.

A colour-blind daughter is born when :

A) Father is colour-blind, mother is normal

B) Mother is colour-blind, father is normal

C) Mother is carrier, father is normal

D) Mother is carrier, father is colour-blind