Advanced Genetics Hypertrichosis

Women have twice the number of X chromosomes as men do – how can this be? This means that they have twice the “gene dosage” for genes on the X chromosome as men.

In order to correct this, one X chromosome is “turned off” and turned into a “Barr Body.” The Barr Body shows up as a dark spot within the nucleus during interphase.

Cells which have the same X chromosome inactivated tend to group together in adult females, forming patches. This means that different patches of the body will express different phenotypes.

For example, hair colour in cats is determined by a gene on the X chromosome. The gene has two alleles: XO (orange) and XB (black).

For males: XOY will be orange. XBY will be black. For females: XOXO will be orange. XBXB will be black.

What about females with the genotype XOXB? Since different patches of skin will have different X chromosomes inactivated some patches will express the orange phenotype some will express the black phenotype The result will be calico:

This means they have Kleinfelter Syndrome Do male calico cats exist? In order to be calico, a cat must have an XOXB genotype. Only way a male can have this is if they have the genotype XOXBY This means they have Kleinfelter Syndrome polysomy X 2 copies of the X chromosome (remember XXY)

The same thing happens in women who have anhydrotic ectodermal dysplasia… patches of their bodies expressing the affected X chromosome have no sweat glands, hair, or teeth. For example:

Barbara McClintock Discovered the method by which “crossing over” of chromosomes or genetic recombination occurs. She did this despite facing considerable sexism, in a field where women were almost universally excluded.

She also discovered that some elements of the chromosome (called “transposons”) can “jump” from one chromosome to another. For this work, Dr. McClintock won the 1983 Nobel Prize in Medicine.

These transposons exist all over the place in nature, especially in simple genomes like those of bacteria. Additionally, bacteria sometimes have circular segments of DNA called “plasmids” which they can “inject” into other bacteria to transmit genetic information.

For example, look at the animation on this web page. This mechanism allows bacteria to transmit antibiotic resistance or other dangerous traits to each other – this can often occur in areas with a large variety of bacteria, such as hospitals.

We can also make use of similar elements of DNA to “repair” genetic abnormalities before the fetus has developed a disorder. This is done by replacing the defective gene with a working copy of the gene in other words, an undesirable allele is taken out and a desirable allele is put in

Controlled Breeding!! For thousands of years before DNA was even known to exist, human beings engaged in a form of “genetic engineering”. Selective breeding: Animals which possess desirable traits are encouraged to breed, while those which do not are prohibited from breeding….examples???? Inbreeding: Animals from the same “family” are interbred to strengthen desirable characteristics. Gene pool becomes limited….examples???? Both forms of breeding can “limit the gene pool”

Using just these two methods, humans have made some amazing changes. This:

Became this:

And this:

Became this: