Ovaries secrete two hormones: oestrogen and progesterone. Oestrogen is involved in changes in the ovaries that lead to ovulation, and the development of secondary sexual characteristics. Progesterone is involved in the growth and maintenance of uterine lining for the embryo.

The sex chromosome pair in males has one X and one Y chromosome. Thus, when male gametes, i.e., sperms are formed, 50% would contain a X chromosome and the other 50% would contain a Y chromosome.

A human cell has 46 chromosomes in total. Out of these 46 chromosomes, 44 are autosomes and 2 are sex chromosomes. Chromosomes occur in pairs and thus there are 23 pairs. A cell having 23 pairs of the chromosome is called diploid. Diploid cells undergo division and their number reduces to half, i.e.  produce haploid cells having only 23 chromosomes, without any pairs. These cells are also called gametes. Thus, gametes have only one sex chromosome.

Iodine is essential for the production of thyroxine. In an attempt to produce more thyroxine, the gland enlarges. This condition is called goitre. 

AIDS is caused by the Human Immunodeficiency Virus (HIV) virus. HIV passes from an infected person to a normal person through sexual contact, sharing syringes, breast feeding etc.