Question

The human offspring can be of two types with XX and …….. chromosomes:
A) XY
B) XX
C) XXX
D) YY

Answer 1

Hint: The chromosome is considered as the basic unit of inheritance. These units help in the transmission of characteristics from one generation to the other. In humans there are twenty- three pairs of chromosomes, where twenty- two pairs are non-sex chromosomes or autosomes, and the last one pair are allosomes or sex chromosomes.

Complete answer:
Human offspring can be of two types male and female and the sex of the baby is determined by the contribution of the chromosome from the father. There are two kinds of sex chromosomes, that is, X and Y type. The different combinations or presence of specific chromosomes determine the gender of the person. In human beings, the female individuals are homozygous, that is their genetic makeup is XX in type. Whereas in males, it is heterozygous, which is XY in nature. That is females can produce only a single type of gametes, that has only X chromosomes. Males can produce two types of gametes, the X and Y gametes. Thus during fertilization, there are equal chances that the zygote produced can be male or female. And the gender of the child is determined by the chromosomes of the father. Therefore the other type of chromosome is XY type.

Figure: Cross depicting the sex- determination in human beings
Considering the other given options:
B. XX depicts the normal chromosomal makeup of females. In males, the genotype is of different arrangement and type. Thus it is not the right option.
C. XXX shows the genotype of a chromosomal abnormality known as the Triple X syndrome. It does not occur in normal genotypic conditions. Hence it is not the right option.
D. YY condition does not exist in human beings. Thus it is not the right option

Thus the most appropriate option is A. That is, apart from XX, the other type of genotype in human beings is XY.

Note:
Unlike in humans where male heterogamety is present, in birds female heterogamety is present that means in this case eggs are of two types, one with Z chromosome and another with W chromosome while sperm is homozygous (produces only Z chromosome). ZW represents females and ZZ represents the male.