UnravellingGenetics>Hereditary>What

How genes work	Mutations	Disease Triggering	Dominance	Example

What are genes?

Genes are operational subunits of DNA. DNA is the information database that carries the complete set of instructions for making all the proteins a cell will ever need.
Each gene contains a particular set of instructions, usually coding for a particular protein. DNA exists as two long, paired strands spiraled into the famous double helix. Each strand is made up of millions of chemical building blocks called bases. While there are only four different chemical bases in DNA (adenine, thymine, cytosine, and guanine), the order in which the bases occur determines the information available, much as specific letters of the alphabet combine to form words and sentences. The nucleus of each cell contains DNA. Every human cell (with the exception of mature red blood cells, which have no nucleus) contains the same DNA, but not all contribute to the appearance of the cell. Each cell has 46 molecules of double-stranded DNA. Each molecule is made up of 50 to 250 million bases housed in a chromosome. The DNA in each chromosome constitutes many genes (as well as vast stretches of non-coding DNA, the function of which is unknown).
A gene is any given segment along the DNA that encodes instructions that allow a cell to produce a specific product - typically, a protein such as an enzyme - that starts one specific action.

The two sets of chromosomes in a human cell are contributed each from the mother and the father. Mature gametes (sperm and egg cells) carry a single set of chromosomes. Each set has 23 single chromosomes - 22 autosomes and an X or Y sex chromosome. (Males get an X from the mother and a Y from the father, while females inherit an X from each parent.)

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