Question

As per Lyon's hypothesis, one of the two X chromosomes undergoes heterochromatisation and is called as

• A. Barr body
• B. Karyotypic body
• C. Genotypic body
• D. Phenotypic body

Answer 1

Answer: (A)

Barr body

The inactivated X chromosome in the somatic cell of the female is referred to as Barr body which is present as tightly coiled and hence, visible heterochromatin. Its number is always one less than the total number of X chromosomes in the cell. According to Lyon’s hypothesis, dosage compensation in human is accomplished by the inactivation of one of the X chromosomes in females. This is done so that both males and females have only one functional X chromosome per cell because human males have only one X chromosome, whereas females have two and hence, twice the genes present on the X-chromosome. Option A is correct. Karyotype refers to the representation of size, shape, and a number of chromosomes, their position of the centromere in an organism. Genotype represents genetic constitution of an organism and expression of genotype in physical traits of the organism is called phenotype; for example “TT” is genotype of an organism while “tall” is the concerned phenotype.