Men Determine Sex Ratio

Photo Credit: David Niblack

A genetics study conducted by researchers at Newcastle University has shown that men with more brothers than sisters are likely to have more sons than daughters. The reverse also holds true if men have more sisters than brothers. It appears that men inherit this tendency from their parents.

Human cells contain 23 pairs of chromosomes which include 22 pairs of autosomes and one pair of sex chromosomes. The sex chromosomes are the X chromosome and the Y chromosome. Fathers determine the gender of their offspring because gender is determined by the type of chromosome (X or Y) that combines with the mother's X chromosome. An (XY) pairing produces males and an (XX) pairing produces females.

Men that produce more Y chromosomes will have more boys, those that produce more X chromosomes will have more girls, and those that produce about the same amount of X and Y chromosomes will have about equal numbers of boys and girls. These tendencies to produce more X or Y chromosomes are passed on through genes from both parents.

Learn more about this study, see:

• Boy Or Girl? It's In The Father's Genes (Science Daily)