Many cat owners seem to long to know more about their cat. What were her parents like? How did they get their colour? I wonder if they have any pedigree in them? Would I get pretty kittens if I bred her? In order to answer these questions, it is essential that you understand genetics and how they work.
This guide will also be of some interest to cat breeders, many of whom still struggle with genetics. As this is fundamental knowledge which should underpin every breeding choice and every aspect of breeding, it is essential to understand how and why things happen in a breeding programme.
A gene is a strand of DNA which codes for one or more molecules or proteins which, in turn, are responsible either for physical make-up, or certain processes within a living body. In very simplistic terms, a gene is akin to a coded message to the body.
A good analogy of how a gene works is to think of a drive-through or restaurant service. You go to the counter, and say “I’ll have number 45 on the menu”. The server writes this down, then takes your order to the kitchen, where the chef produces the burger and chips which corresponds to number 45 on the menu, and sends it back to you via your server. Your coded message, in this case the gene, has triggered the making of your burger, i.e. the protein.
To make it slightly more complex, the DNA strand codes for the protein indirectly through RNA. In the above example, RNA would be your server, but in order to explain fully, we need to look at what DNA actually is.
DNA, or deoxyribonucleic acid, is a double helixed arrangement of only four different molecules. These are Guanine, Adenine, Thymine and Cytosine. Together with the sugar deoxyrybose, they are the building blocks which code for the formation of every living thing. The four molecules are arranged in different patterns, with the sugar acting as a backbone to keep them in place. Two similar strands of DNA bond base to base, and in doing so, they twist to form a double helix. These are arranged in long strands called chromosomes. Chromosomes are X shaped and come in pairs. There are 26 of these in each cell. Males have one chromosome which has a leg missing. This is why females are termed to be XX and males XY, and can explain why sex-linked conditions can be more common in males than females.
There are only so many ways to arrange four different molecules (properly called bases) you might think, but DNA is not read in only blocks of four. A single strand of DNA can have thousands of bases in thousands of different patterns. This means that coding possibilities are endless. However, in order to code, the bases must be visible, and this involves a DNA split. An enzyme encourages this to happen, thus freeing the base pairs for bonding. RNA molecules then use a key and lock system to place other base molecules onto the now naked strand of DNA. Once these molecules are bonded into a chain, the DNA reseals itself, and RNA travels to a different part of the cell for processing to code the final product.
It is one thing to understand what DNA is and how it codes for things, but in physical terms, this is going to be most important when breeding. Therefore, it is important to appreciate how genes make it to the new baby.
Sex cells, i.e. spermatozoa and ova (eggs) are unique in their structure. Rather than having pairs of chromosomes, they only have one of each pair. When sex cells are formed, pairs of chromosomes split in half. Each half moves to opposite ends of the cell (the selection of which half goes where is random and not logical). The cell then narrows in the middle until it splits into two.
When the cells of males and females meet, they are each carrying exactly half of the genetic material needed to make a baby. When they join, each cell exchanges genetic material in a glorious mix. Because of the cross-over between parent chromosomes, the offspring will not be a genetic copy of mum or dad, or even half of each. Genes combine and switch places to give each living thing a unique genetic make-up.
Fun fact: As females only possess X chromosomes and males possess XY, it is the male who exclusively decides what sex the offspring will be.
For further information on genetics specific to cats, please continue with other articles in the Cat Genetics series.