noun, plural: Y chromosomes
A sex chromosome is a type of chromosome responsible for the chromosomal determination of the sex of an individual. In humans and other mammals, there are two forms of sex chromosomes: the X chromosome and the Y chromosome. The sex chromosomes in males are X chromosome and Y chromosome; females have a pair of X chromosomes. In this XX/XY sex-determination system, the sex of an organism is determined by the sex chromosomes since these chromosomes bear the genes that control the development of reproductive organs and other sexual characteristics of an individual.
Nattie Stevens was the first to describe the Y chromosome in 1905. The X chromosome, though, was first to be discovered (i.e. in 1890 by Herman Henking) before the Y chromosome. For being the next chromosome to be discovered after the "X" chromosome, it was named "Y". Hence, the Y chromosome did not get its name from resembling the letter "Y" during mitosis although it does look like it due to its very short branches that appear to merge. Stevens was correct when she proposed that it is the Y chromosome, and not the X chromosome, that determines sex.
The Y chromosome is relatively smaller than the X chromosome. It also bears fewer genes. In humans and other mammals, the Y chromosome bears the Sex determining Region Y (SRY) gene. The SRY gene codes for the SRY protein that is involved in the testicular development in many male mammals. It is particularly located on the so-called sex-determining region of the Y chromosome. Apart from genes associated with sex determination, there are other genes linked to the Y chromosome. Thus, there are traits and genetic disorders manifesting in the son as passed on from the father. This type of inheritance is referred to as Y-linked inheritance.