Practicing Success

Target Exam

CUET

Subject

Biology

Chapter

Principles of Inheritance and Variation

Question:

Read the given passage and answer the following questions :    
Mendelian disorders are mainly determined by alteration or mutation in the single gene. These disorders are transmitted to the offspring on the same lines as we have studied in the principle of inheritance. The pattern of inheritance of such Mendelian disorders can be traced in a family by the pedigree analysis. Most common and prevalent Mendelian disorders are Haemophilia, Cystic fibrosis, Sickle cell anaemia, Colour blindness, Phenylketonuria, Thalassemia, etc. It is important to mention here that such Mendelian disorders may be dominant or recessive.

Why are females less likely to be color blind compared to males?

Options:

Females have two X chromosomes, so the normal gene on one X chromosome can suppress the effect of the recessive gene on the other X chromosome.

Females have a stronger immune system

Females have fewer cone cells in their eyes

Females have a different visual cortex

Correct Answer:

Females have two X chromosomes, so the normal gene on one X chromosome can suppress the effect of the recessive gene on the other X chromosome.

Explanation:

The correct answer is Option (1) -Females have two X chromosomes, so the normal gene on one X chromosome can suppress the effect of the recessive gene on the other X chromosome.

Colour Blidness 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 per cent of males and only about 0.4 per cent 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 per cent chance of being colour-blind. The mother is not herself colour blind because the gene is recessive. That means that its 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.