Question

An example of sex influenced inheritance is
A) Haemophilia
B) Baldness
C) Colour Blindness
D) Down’s syndrome

Answer 1

Hint: Sex-influenced traits are autosomal traits that are expressed based on the influence of the sex, in particular, the sex hormones.

Complete answer:
Let’s discuss given options and find the correct answer:
>Option A: Haemophilia is a sex-linked recessive disorder. The abnormal gene responsible for haemophilia is carried on the X chromosome. Sex-linked is a trait in which a gene is located on a sex chromosome.Therefore, this is an incorrect option.
>Option B: Sex-influenced traits are autosomal traits that are expressed based on the influence of the sex, in particular, the sex hormones, e.g., testosterone in males and estrogen and progesterone in females. It is a phenotypic characteristic or trait such as male pattern baldness that is expressed differently in males and females. Although these traits can be observed in both the sexes, it varies according to the degree or frequency of the phenotypic expression in both the sexes. The genes are dominant in males but recessive in females. In the case of baldness, B+ is dominant in males but recessive in females and, hence, requires 2 B+ to cause baldness in females. Also, the presence of testosterone levels influences the expression of the baldness allele. Higher levels of testosterone hormone in males cause the baldness gene to be dominant while lower levels in females make it recessive. This trait is also called male pattern baldness. Therefore, this is the correct option
>Option C: Colour blindness is a genetic condition which is passed to offspring from parents. The gene which is responsible for the condition is present on the X chromosome. It is an X-linked recessive condition. The affected individuals cannot distinguish between red-green colour. Therefore, this is an incorrect option.
>Option D: Down’s syndrome is a genetic disorder caused when abnormal cell division results in extra genetic material from chromosome 21. Abnormal cell division results in an extra full or partial copy of chromosome 21. Therefore, this is an incorrect option.

Hence the correct answer is option ‘B’.

Note:It is to be noted that the presence of androgenic hormone levels also influences the expression of the hairlessness gene. Androgenic hormones are those hormones which have a role in male traits and examples of androgenic hormones are testosterone.