Question

XX males and XY females are too rare to occur in human populations. If it happens so it would be due to
A. Genes of Y chromosome are on X
B. Crossing over occurs between X and Y
C. Nondisjunction of chromosomes
D. All of the above

Answer 1

Hint: XY are generally males and XX are females but there are cases where persons with XY chromosomes are known to be females and vice versa. . Other genes than X and Y also contribute to sex development.

Complete answer:
The sex of a person is determined generally by examining his/her sex chromosomes. If the set of chromosomes found is to be XX, the sex is concluded as female and if the set of chromosomes is found to be XY, the person is identified as a male but there exist some exceptions.
Some females with XY set of chromosomes and males with XX set of chromosomes are also found to be existing. This happens when the Y chromosome’s genes lie on the X chromosome. This displacement results in the functioning of the X chromosome like that of Y.
The females with XY set of chromosomes suffer from syndrome known as Swyer syndrome. It is a condition of hypogonadism. The person suffering from this syndrome possess external genitalia same as that of a normal female. This type of syndrome occurs due to abnormal development of gonads, chromosomes and sex organs.
This syndrome is also known as 46, XY. It is the dysgenesis of the gonadal tissue. This is a syndrome in which the person with XY chromosomal pattern (which is commonly found in males) have reproductive structures same as those of females.
The gonads, that is, ovaries or the testis are found but are not functional. This syndrome along with sexual development and activities also affects the nervous system.

So, the correct answer is (A).

Note: The outer appearance of persons suffering from Swyer syndrome or their phenotype, is female but they have XY set of chromosomes.