Animal World - cat genetics: interaction between genes

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nteraction etween enes

Chromosomes contain the genetic material for the species. The genetic material of one individual property of that species is called a gene. There are thousands of genes stored in a single chromosome, each responsible for a specific individual property.
Just like chromosomes make pairs, genes who are at the same location on those chromosomes also form a pair. The majority of those genes are not interesting and we don't know much of them.
cat with biiiiiiiiiiig eyes For example: there are somewhere in the chromosomes genes responsible for the fact that a cat has 2 eyes (see pic :-). But why bother looking for them when all cats have 2 eyes? At the moment that cats are frequently born with one eye it is a different story!!!

The interesting genes (for us, the no-scientists) are those who have mutations. Normally cats have short hair, but a long time ago the first cats with long hair were born. The original gene for short hair is in the cells of long haired cats (Persians) replaced by a mutant gene that is responsible for long hair.

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As mentioned before genes form pairs, but what happens when a original gene and its mutant form a pair? It's quite simple, one of the two will be the strongest. When a cat has one gene for long hair and the other one is for short hair, the cat will appear as a normal shorthair, because the gene for short hair is stronger then the gene for long hair.

The strongest gene is called the dominant gene and the weaker one is called the recessive gene.
The symbol for a gene is a capital or the small letter of the Latin alphabet.
The capital is the symbol for the dominant gene, the small letter for the recessive gene.

xample

Genes used in our example are D and d. D is the original and dominant gene that stands for deep, it gives the coat a deep, dark color. The gene d is standing for dilution, it can change a black cat into blue and a red cat into cream.
The only way to get a blue cat is by giving it 2 genes for dilution (d) because we are talking about recessive genes.
When a cat has 2 identical genes we call it homozygous, when a cat has 2 different genes he or she is heterozygous.

The combination DD and Dd give both a black cat, and you can't see on the outside of the cat if he is DD or Dd.
The outward appearance is referred to as the phenotype, and the genetic constitution as the genotype.
If only recessive genes are involved the phenotype is the same as the genotype.
A blue cat has always the genotype dd but when dominant genes are involved it's not so easy.
Just by looking at a black cat we can't see if the genotype is DD or Dd.
We know for sure that it has at least one D gene, so we write this as D-.

Sometimes we can find the correct genotype by looking at the parents of the cat. If the parents of the black cat are blue and black, we know that his genotype is Dd.

Another way to find the genotype of the black cat is by crossing it with a blue cat. When there are blue kittens you know for sure that the black cat has Dd as genotype.