Chromosomes are thread-like molecules that carry hereditary information for everything from height to eye color. They are made of protein and one molecule of DNA, which contains an organism's genetic instructions, passed down from parents. In humans, animals, and plants, most chromosomes are arranged in pairs within the nucleus of a cell. Humans have 22 of these chromosome pairs, called autosomes.
How do XY chromosomes determine sex? | Yahoo Answers
Male vs Female Chromosomes. Male and female chromosomes are the sex determining chromosomes of an organism. These are also known as gonosomes. Numerous models are used for sex determination in organisms. XY system is used by humans, most mammals, some insects, and some plants.
XY sex-determination system
An allosome also referred to as a sex chromosome , heterotypical chromosome , heterochromosome ,   or idiochromosome  is a chromosome that differs from an ordinary autosome in form, size, and behavior. The human sex chromosomes, a typical pair of mammal allosomes, determine the sex of an individual created in sexual reproduction. Autosomes differ from allosomes because autosomes appear in pairs whose members have the same form but differ from other pairs in a diploid cell , whereas members of an allosome pair may differ from one another and thereby determine sex. Nettie Stevens and Edmund Beecher Wilson both independently discovered sex chromosomes in However, Stevens is credited for discovering them earlier than Wilson.
The nuclei of human cells contain 22 autosomes and 2 sex chromosomes. In females, the sex chromosomes are the 2 X chromosomes. Males have one X chromosome and one Y chromosome.