Genetics follow some basic rules.Firstly there is always 2 genes that work to express a trait, each trait has its own locus. A locus is defined as a place on a chromosome where a gene is located. There may be more than 2 different genes that can be located at a given locus.
Some genes are dominant, some are recessive. Dominant means that if that gene is present it will express itself, it only takes 1 copy for a dominant gene to be expressed. Recessive means that in order for a specific trait to be expressed there must be 2 copies of that gene. Some genes are both dominant and recessive. There are genes that are incompletely dominant. What this means, is that if there are 2 copies the trait will be expressed more fully and, when only 1 gene is present the trait will be expressed, but to a lesser degree.
Once you understand that 2 genes are required to express a trait, the next step is to understand Homozygous and Heterozygous. Homozygous means that there are 2 copies of the same gene at a certain locus. Homozygous therefore means that the animal can only pass on one type of gene from that particular locus. Heterozygous, on the other hand, means that there are 2 different genes located on the same locus. Heterozygous means that the animal has a possiblity of passing either one or the other gene on.
The other big thing to understand when talking about genetics is that each parent passes on 1/2 of its genes to each offspring. There are many different combinations of genes working together to make an individual what it is. There for there are many different combinations of genes that can be passed on. It all depends on what genes are in the 1/2 that get passed on.