Question

If somatic cells of a human male contain a single Barr body, the genetic composition of the person would be?
A. XYY
B. XXY
C. XO
D. XXXY

Answer 1

Hint: Aneuploidy in chromosomes involves the incorrect or any error in the number of chromosomes within a cell. This aneuploid state can give rise to many genetic abnormalities in the individual.

Complete answer:
An inactive copy of the X chromosome, which is present within a cell containing more than one X chromosome. These chromosomes get inactivated during the process of embryogenesis. The number of Barr bodies present within a cell would always be one number less than the number of X chromosomes present in the cell. Since in this person, there is a single Barr body present, the number of X chromosomes would be two. Since the person is a male he would also be having a Y chromosome. Thus the genetic composition would be XXY. This genotype is present in individuals affected by Klinefelter's syndrome.
Considering the other given options:
XYY is a chromosomal disorder in males due to the presence of an extra copy of the Y chromosome. This can be caused due to an error during the process of spermatic cell division. Thus it is not the appropriate answer.
XO is the genotype of Turner’s syndrome that affects females. It is the absence of an X chromosome. The affected individuals would be short-statured, with underdeveloped ovaries as well as breasts. The individuals would be sterile. Thus it is not the right option.
XXXY is a very rare genetic disorder caused due to the presence of several X chromosomes and a single Y chromosome. The affected individuals would be mentally retarded, and would have short stature as well as hypogonadism.
Thus, from the above-given options, the most appropriate answer is B. That is, in a human male containing a single Barr body, the genotype of the individual would be XXY.

Note: The barr bodies are usually inactivated chromosomes. But the reactivation of these chromosomes is possible. It is seen in several patients affected by breast cancer. Thus the reactivation of these barr bodies by mutation can be a cause of breast cancer.