Apr 25, 2010

DNA Testing/Character Resemblance

*Note: the picture on the left has nothing to do with DNA testing, I just thought it was great! :-)

So, you're doing your character sketch and wondering about the genetics of recessive eye coloring. You have two people with blue eyes, so what color would the babies be? Blue. Why? Blue is a recessive gene. In order to disrupt the blue gene, you need to sprinkle in a dominant color, i.e. brown. The scientific explanation is below:

This is the simplest case of dominance. The allele that produced the working protein would be dominant over the allele that produced the defective protein. Individuals with two copies of the working allele and individuals with one copy of the working and one copy of the defective allele would both be able to produce working protein. Only individuals with two copies of the defective allele would be unable to produce working protein. The allele that produces this defective protein would be recessive to the allele that produces the functional protein.

Dominance can also be produced by other differences between the protein products of alleles - a recessive allele does not mean a defective gene product. Dominant and recessive should be taken only as descriptions of the expression of alleles, and not given any value judgement. Blue eyes are not worse than green or brown eyes.

Dominant and recessive flavors of genes and the presence of genes on chromosomes that come in pairs can explain the eye color inheritance patterns described here (but remember that there is more to human eye color inheritance than the simple two gene model described here).

The bey2 gene has two flavors - brown is dominant over blue. Each individual has two copies of this gene, each can be one of the flavors. The possible allele combinations for the bey2 gene are: brown-brown, brown-blue, and blue-blue. Of these three, the brown-brown and brown-blue combinations will both produce brown eyes, as brown is dominant over blue. Only the blue-blue combination will produce blue eyes.

But there is a second common gene for eye color - the gey gene. It also has two flavors - green is dominant over blue. In addition, a green allele of gey is dominant over a blue allele of bey2 and recessive to a brown allele of bey. Thus the alleles of the two genes have a dominance hierarchy - bey2-brown is dominant over everything else, gey-green is dominant over bey2-blue and gey-blue but recessive to bey2-brown, and both of the blues are recessive to everything else. Thus the bey2 (brown/blue) gene might be better thought of as the brown/non-brown gene.

To tie this into a nice easy explanation, let us try...

Chromosomes are long, stringy aggregates of genes that carry heredity information. They are composed of DNA and proteins and are located within the nucleus of our cells. Chromosomes determine everything from hair color and eye color to sex.

Human genetics. A discipline concerned with genetically determined resemblances and differences among human beings. In normal humans, the nucleus of each normal cell contains 46 chromosomes, which comprise of 23 different pairs.

The final piece of the story (and remember, it is just a story, there are more than just these two genes involved in eye color inheritance) is that a child gets one chromosome of each pair from each parent. The bey2 gene is on chromosome 15. A parent with brown-blue alleles of the bey2 gene has a pair of chromosome 15s, with the brown allele on one and the blue allele on the other. This parent could give either the chromosome bearing the brown allele or the chromosome bearing the blue allele to a child. A child with brown-blue alleles of the bey2 gene got the brown allele (and one copy of chromosome 15) from one parent, and the blue allele (and the other copy of chromosome 15) from the other parent.

If you are looking for those dominant traits, check the simple inheritance patterns.
A few dominant traits are: Widow's peak, facial dimples, unattached earlobe, cleft chin, brunette iris, color vision, brunette hair, normal nose, ability to roll tongue, normal pinkies, normal thumb, freckles and wet-type earwax.

Science, don't cha just luv it? Enjoy those critical character items.

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