dbowyer68rr -- I teach this stuff so I'll give you a quick overview of what 'het' means.
On any one chromosome strand genes exist as pairs along the strand. One of the pair comes from the father and the other from the mother. Where each pair of chromosomes are located is called a loci (simply a location). When the genes that code for a particular character, color for instance, are the same at a loci they are said to be HOMOZYGOUS, that is, they are the same (as in Homogeneous). When the genes at a loci are different from one another, say one is a gene for dark color and one is the gene for light color, they are said to be HETEROZYGOUS, and that is where 'het' comes from (like in Heterosexual -- man and woman -- both different in the pair).
Now, in all animals the characteristics that the genes code for (or are responsible for creating) can be either dominant or recessive. A dominant gene will express itself at the expense of the recessive one. In other words, if the gene for dark color was dominant and the loci for color had one dark color gene and one light color gene, then the color of the animal would be dark because of the dominant dark gene overpowering the light color gene. The animal would then be said to be Heterozygous for the dark color gene. In an animal that had two light color genes at the same loci, the animal would be light colored because there are two recessive light genes at the location and no dark gene to overpower it. This light colored animal would be Homozygous for the light color gene.
Let's take a real example from Corn snakes. The color in animals is largely controled by dark pigments called Melanins and red and yellow pigments called Carotins. A combination of the two Carotin pigments (red and yellow) gives the oranges (red and yellow paint together make orange) found in animals and some plants. An albino animal has no pigments, that is no Melanins or Carotins and therefore is just white. An animal that is melanistic has no Carotins and so is just very dark, usually black. And, it so happens that the gene that codes for the presence of Melanin in animals is a dominant gene.
Amelanistic Corn snakes are white bodied with red and orange color patterns, some may have a little bit of yellow here and there. The reason they are this color is because they have no gene for the dark coloration or no gene for the Melanin pigment, but they still have the genes for the presence of the Carotins which give them the red and oranges. These Carotin genes exist as a homozygous pair and are recessive to the dominant melanins. If two Amelanistic snakes are mated they will produce all Amelanistic offspring because they are homozygous for the color trait (the absence of the melanins in this case).
Now, if a Normal Corn snake that is Homozygous for the presence of the dark pigments (two genes for the presence of melanins) is mated with an Amelanistic snake, then all the offspring will be Normal colored. That is because each snake gets one color gene from each of its parents and if each snake gets one dominant dark gene from the Normal corn snake then that gene will overcome the recessive gene (the absence of melanin gene) and give all the young Normal color.
To calculate the results of matings from this point on it is a statistical or numbers game and you need to know what the genetic makeup of the parents are, for instance are they 'het' or 'homo', dominant or recessive for a particular gene. For instance, if a snake 'het' for the normal color (one gene for melanin and one for the absence) was mated with an Amelanistic snake (two genes for the absence of melanin), then 50% of the offspring would be Amelanistic (and homo for the normal color) and the other 50% would be Normal color (and het for the normal and Amel color). If two Normal snakes were bred that were het for the presence of melanin then 25% of the offspring would be Amels (homo for the absence of melanin), 50% would be Normal but het for the melanin gene and the last 25% would be Normal color and homozygous for the melanin gene.
If you sit and think about it, it all makes perfect sense.
