Some people’s biology may set them up to birth babies of a certain sex, explaining why a family with multiple children may have all girls or all boys.

Families with three or more boys, for example, are more likely to have another boy than a girl as the next child.

Sex chromosomes, chromosomes responsible for determining if a mammal is male or female, may have evolved to reduce “sexual ...

Most mammals, including humans, have two sex chromosomes, X and Y.One sex chromosome is usually inherited from each parent, and they pair up as either XX or XY in every cell of the body.. People ...

Almost immediately, however, scientists began to realize there was much more to the story. Just four years after Stevens’ discovery, Thomas Hunt Morgan, an evolutionary biologist at Columbia ...

Human sex chromosomes originated from a pair of autosomes, the ordinary or non-sex chromosomes that contain the majority of our genome and come in identical pairs. That ancestral pair of autosomes ...

The sex chromosomes of insects are thought to be around 450 million years old but have gone through more change over that time. Chromosomes determine the sex in humans and most mammals, but Kern said ...

Analysis of these sex chromosomes revealed that the ancestral X chromosome of monotremes had exchanged segments with ancestral non-sex chromosomes (autosomes), which gave rise to their complex system.

Stevens' sex-chromosome discovery "was the culmination of more than 2,000 years of speculation and experiment on how an animal, plant or human becomes male or female," Stephen Brush wrote for "The ...

Given the dramatic difference in the size and sequence of the human X and Y chromosomes, it’s hard to imagine that they were once a perfect matching pair. But in fact all sex chromosomes start out ...

Intersex people are born with genitals, chromosomes, or internal reproductive organs that don't fit typical male or female patterns and may not match their sex assigned at birth. Find out more.