They decide if a person is male or female. If a person has a missing chromosome it is called monosomy.
Alterations in behavior or the environment, such as diet, exercise, exposure to toxic agents, or medications can all have influences on traits that are at least in part genetically determined.
To understand how genes work, let's review some biology basics.
Heredity plays an important role, but your environment including things like the foods you eat and the people you interact with also influences your abilities and interests.
Single-gene disorders: occur when an alteration occurs in a gene causing one gene to stop working. You can also have three copies of a chromosome, known as a trisomy, or only one chromosome, instead of the normal pair.
A female has two X chromosomes, and a male has one X and one Y chromosome.