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Gene Tyranny


QUESTION

(From yesterday) I'm confused about genes and chromosomes. Could you explain a little about their function?


ANSWER

What kinds of jobs do genes do? We've know that genes are responsible for blood type, but virtually all the functions of the cell are under genetic control:

· The production of energy within the cell. · Signaling from the outside to the inside of cells. · General maintenance of cellular processes, such as protein and RNA synthesis and degradation. · Maintaining or changing cell shape. · Special cells make special gene products such neurotransmitters, bone, hormones, etc. · There are genes that establish the body pattern of the organism during early inter-uterine growth. · Specialized genes are responsible for initiating the cycle of cell division.

Chromosomes, composed of protein and DNA, are distinct dense bodies found in the nucleus of cells. Each chromosome contains a few thousand genes, which range in size from a few thousand bases up to 2 million bases. During most of the cell's life, chromosomes are not visible as individual objects under the light microscope, as the DNA is largely unwound so that it can be copied to RNA. However during cell division, the DNA winds up very tightly and the chromosomes become highly condensed and visible.

Human cells have a total 46 chromosomes, 22 pairs with one of each contributed by the mother and father, and two chromosomes which determine sex; two X chromosomes for females, an X and a Y chromosomes for males. Each pair of chromosomes is numbered from 1 to 23.

Each chromosome pair is joined at the center at a spot called the centromere. The characteristic 'banding' of chromosomes you will see in the picture here is obtained by staining with various dyes. The band width and the order of bands is characteristic of a particular chromosome - a trained cytogeneticist can identify each chromosome (1,2,3...22, X and Y) by observing its banding pattern under the microscope.

Chromosomes are divided into 2 legs; a "p" leg above the constriction point at the waist, and a "q" leg below it. By combining the chromosome number, the p or q leg and a particular band number it is possible to construct an address for a particular gene.

The gene for ABO blood group is on chromosome 9, band 34, on the "q leg." Thus its location is often referred to as "9q34."




The Ask Dr. D'Adamo internet advice column ran from 1996 to 2009, at which time Dr. D'Adamo's teaching and programming responsibilities no longer allowed him to devote time and resources to directly answering visitor questions. However we've recently reorganized this treasure-trove of material and made it again available to his readership. He occasionally posts new entries. These are marked with a NEW tag.



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