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Genetic Structure - Page 3


In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure.

Image from The Genetics Home Reference, NIM, NIH

Each chromosome has a constriction point called the centromere, which divides the chromosome into two sections, or "arms."

The short arm of the chromosome is labeled the "p arm." The long arm of the chromosome is labeled the "q arm."

The location of the centromere on each chromosome gives the chromosome its characteristic shape, and can be used to help describe the location of specific genes.

Normally all humans have 23 pairs of chromosomes. 22 pairs of these chromosomes are identical or autosomal chromosome pairs plus a set of sex chromosomes (XX) for female or (XY) for male.

In each chromosome there resides about 25,000 different genes. In each pair of genes, one comes from mom and one from dad. This is a protective mechanism so that if one of the genes gets hurt the other gene can fill in and keep you healthy.



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