Humans have 46 chromosomes. Chromosomes are long pieces of DNA contained in the nucleus of cells. In the nucleus of each cell there are a total of 23 pairs of chromosomes or 46 total chromosomes. The only other DNA in cells is contained in another part of the cell called the mitochondrion. Mitochondria have important genes on their own DNA strand sometimes called 'the 47th chromosome'. The body's genes are contained within these 46 nuclear or 1 mitochondrial chromosomes.

Two of the chromosomes (the X and the Y chromosome) determine sex and are called the SEX CHROMOSOMES. Females have 2 X chromosomes and males have 1 X and 1 Y chromosome. The Y chromosome determines the male sex, but does little else.

The remaining 44 chromosomes are called AUTOSOMAL CHROMOSOMES. Chromosomes exist in pairs. For convenience, scientists have numbered the autosomal chromosome pairs 1 through 22. The X and Y chromosome are the 23rd pair.

Each parent contributes one half of each pair or 23 chromosomes to their child, 22 autosomal and 1 sex chromosome. Females always contribute an X chromosome to the child while a male may contribute an X or a Y. Therefore, it is the male that determines the sex of the child.

All of the mitochondrial chromosome comes from the mother. Fathers make no contribution to the mitochondrial genes of their offspring. This is called maternal inheritance.

RELATED TOPICS:
Autosomal dominant
Autosomal recessive
Genetic counseling and prenatal diagnosis
Sex-linked dominant
Sex-linked recessive

For detailed information, see heredity and disease (genetics).