ABC of genes & chromosomes: --In humans, genes vary in size from a few hundred DNA bases to more than 2 million bases. The Human Genome Project estimated that humans have between 20,000 and 25,000 genes. Every person has two copies of each gene, one inherited from each parent .
A gene is the basic physical and functional unit of heredity.
Genes are made up of DNA. Some genes act as instructions to make molecules called
proteins. However, many genes do not code for proteins. The Human Genome Project estimated that
humans have between 20,000 and 25,000 genes.
Every person has two copies of each gene, one
inherited from each parent. Most genes are the same in all people, but a small
number of genes (less than 1 percent of the total) are slightly different
between people. Alleles are forms of the same gene with small differences in
their sequence of DNA bases. These small differences contribute to each
person’s unique physical features.
Scientists keep track of genes by giving them
unique names. Because gene names can be long, genes are also assigned symbols,
which are short combinations of letters (and sometimes numbers) that represent
an abbreviated version of the gene name. For example, a gene on chromosome
7 that has been associated with cystic fibrosis is called the cystic
fibrosis transmembrane conductance regulator; its symbol is CFTR.
Genes are made up of DNA. Each chromosome
contains many genes.
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