What are consequences of XX females and XY males for traits on their sex chromosomes?
• Note that unlike autosomes which come in homologous pairs during meiosis, the X and Y are not the same in size or the genes they contain. • None of the genes on the Y are essential for life. Females do quite well with two X chromosomes and no Y chromosome (in fact, they live longer than males). • There are only some 16 genes on the Y and most are associated with sperm production and testes formation. • The X is a typical chromosome. It contains several thousand genes. Most of those genes have nothing to do with sex determination or sexual traits. • In the XY male, genes on the X are expressed whether they are dominant or recessive. The male is thus called hemizygous for the X because the Y acts as if it doesn’t exist with respect to the X. • In the XX female, the genotype is like an autosome: it can be for any allele either homozygous normal, homozygous recessive, or heterozygous. • What are the consequences of hemizygous inheritance in the male? • In humans certain traits are seen i
