Question

When released from the ovary, the human egg contains how many sex chromosomes?
A) One Y Chromosome
B) One X Chromosome
C) Two X Chromosomes
D) XY Chromosomes

Answer 1

Hint: This chromosome was discovered and named by a cytologist, Hermann Henking in the 1890s. This chromosome contains around 150 million base pairs which represent around 800 protein-coding genes.

Complete answer:
All-female humans have two X chromosomes in all their cells, while all males have an X and a Y chromosome in all their cells. All cells in the body undergo mitotic divisions as a mode of reproduction for the individual cells. The germ cells in both males and females undergo meiosis (which reduces the number of chromosomes to half).

When the germ cells in males undergo meiosis, all the chromosomes of one cell gets distributed among two daughter cells. Since males have one X and one Y chromosome, one of the daughter cells receives an X chromosome and the other receives a Y chromosome. These cells then develop and form two different sperm cells having one X and one Y chromosome respectively.

Similarly, when the germ cell in females undergoes meiosis, both of the daughter cells receive an X chromosome each. This is because the germ cell in females has two X chromosomes and no Y chromosome. These two daughter cells then develop and form two human egg cells or ova.

Therefore, the human egg cell contains one X chromosome when it is released from the ovary. Thus option ‘B’ is the correct answer.

Note: Sometimes this separation of chromosomes does not take place properly. This leads to one ovum having two XX chromosomes or one sperm having both X and Y chromosomes. In such cases the zygote thus formed will have chromosomal abnormalities. Some examples of such abnormalities are Klinefelter Syndrome (XXY condition), Super female syndrome (XXX condition), etc.