Katherine Reece Wrote:
-------------------------------------------------------
> ~sigh~ I'm sure I'll be sorry I asked you this
> question ........
>
> But if not random how do you explain that my
> parent's had four children ...
>
> 1st child - dark hair
> 2nd child - red hair
> 3rd child - blonde hair
> 4th child - blonde hair
>
> All however with green eyes
1) The following from G.J. Stine, 1977. Biosocial Genetics NY: Macmillan pp. 260-262.
"Blue-,gray,green- and pink- appearing eyes are optical phenomena. Eyes do not contain those individual pigments. An eye merely loks blue, green or a shade of gray. The gene responsible for the variously colored eyes apparent in the population controls the production of the pigment melanin. Melanin varies in color from black or dark brown to shades of light yellow. The variety of eye colors results from the reflection of light, which is affected by the different size, shape , and the number of melanin particles present in the iris of the eye.
When dark-eyed people mate with dark- or blue-eyed people, they generally produce dark-eyed children. Brown-eyed people mating with brown- or blue-eyed people generally produce brown-eyed children. and mating between two blue-eyed people produce blue-eyed children. Such data suggest that the dark or brown trait, B, is dominant over blue,b.
In dark eyes a black to dark brown melanin is heavily deposited on the front of the iris. In blue eyes there is a light deposit of tiny melanin granules on the rear of the iris. Incoming light, which meets no refletive surface until it meets these tiny granules in the back of the iris, is reflected back to the surface of the iris as blue. The pigment is not blue, nor is the iris. The phenomenon is an optical illusion. It is similar to the way scattered light reflected off dust particles gives the sky such beautiful shades of blue.
In green eyes the pigment in the rear of the iris is similar to that of the blue eyes; however, a lighter-colored or yellowish brown melanin is deposited on the front of the iris. the reflectd light now shows the combined effects of blue integrated with the brown-to-yellow pigment and appears green. Additional pigment in the front of the iris results in gray-yellow or gray-brown eyes."

{BOM]genes for low production of melanin would combined with the gene indicating where the granules of melanin would be located would account for the green eyes and would be compatible with the parental genotypes I proposed below.


2) Blond hair is recessive for the production of a lot of melanin i.e. to get it you must get it from both parents (bb), Black or brown hair is dominant (i.e. either BB coming from both parents or bB with the B coming from one parent). Red hair involves a wholly different gene that codes for the production of red coloring. This is why a person with black hair can have stands of red hair at the same time, giving a chestnut hue, if enough red strands are present. Also red hair can be found on people with any eye color.
thus your sibling with dark hair is (BB or Bb and could be rr or possibly Rr)
sibling with red hair is (bbRr) red hair or (BbRr) Strawberry blond, the blond siblings are (bbrr).
By working backwards and knowing that the particular combination of genes coming from the mother and father are random (pace WG) we can propose the following (I won't specify whether mother or father-- you would have to go back in the family tree to see who had red hair)

Parent 1 (BbRr) Parent 2 (bbrr)
Parent 1 (BbRr Parent 2 (Bbrr)

Bernard


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Edited 1 time(s). Last edit at 04/17/2005 04:57PM by bernard.