In most species, sex is determined by the presence or absence of special chromosomes. As a result of meiotic segregation, each gamete has one sex chromosome to contribute at fertilization. The chromosomal basis of sex in humans Mammals, including humans, have an X-Y mechanism that determines sex at fertilization. Whether an embryo develops into a male or female depends upon the presence of a Y chromosome. Some genes on sex chromosomes play a role in sex determination, but these chromosomes also contain genes for other traits.
Fathers pass X-linked alleles to all their daughters only.
If a sex-linked trait is due to a recessive allele, a female will express the trait only if she is homozygous. Because males have only one X-linked locus, any male receiving a mutant allele from his mother will express the trait. In female mammals, most diploid cells have only one fully functional X chromosome. Errors and Exceptions in Chromosomal Inheritance A. Alterations of chromosome number or structure cause some genetic disorders Meiotic errors and mutagens can cause major chromosomal changes such as altered chromosome numbers or altered chromosomal structure. Alterations of chromosome structure Chromosome breakage can alter chromosome structure in four ways.