Sex is determined by a pair of sex chromosomes
. In males, there are is one X chromosome
and one Y chromsome
), and in females there are just two X chromosomes (XX
). A sex-linked trait, is a trait that is carried by one of these chromosomes. Except for several rare
exceptions, the X chromsome carries all sex-linked traits, and the Y chromosome's sole purpose is to determine sex
. This means that if you have any given trait, only females will ever be heterozygous
, because males will never have more then one gene
for a particular trait.
This can be demonstrated in a Punnet Square
. Typically, you cross a male
with a female
and put each version of the genes as an exponent. You then combine the genes and exponents like you normally do in a punnet square.
Courtesy of my biology class