Sex Chromosomes and Sex Determination
The sex of each kitten is decided by a pair of chromosomes known as the sex chromosomes; all other chromosomes being known as autosomes. The characters inherited along with the sex chromosomes are known as sex linked or sex limited characters and those inherited irrespective of the sex chromosomes are known as autosomal characters. Sex limited characters are caused by genes that can affect only one sex because of the sex chromosome on which they are inherited or because of the physiological differences between sexes. In man there is a gene, inherited along with the Y chromosome, causing him to have hairy ears. An example of a sex linked gene in the domestic cat is red coat color (described by geneticists as orange) and an example of an autosomal character in the cat is agouti.
There are two types of sex linked chromosome -- the X chromosome and the Y chromosome. The female cat has an identical chromosome pair XX and the male has a dissimilar pair XY. All the ova produced by the female will have only one X chromosome in addition to the autosomes while all the spermatozoa produced by the male may have either an X or a Y chromosome in addition to the autosomes. In other words the female is only capable of producing eggs with an X chromosome while the male will produce equal numbers of spermatozoa carrying Y and X. If the ovum is fertilized by a spermatozoon carrying the X chromosome then the resultant kitten will have two X chromosomes (XX) and will be a female. If, on the other hand, the ovum is fertilized by a spermatozoon carrying the Y chromosome then the resultant kitten will have one X chromosome and one Y chromosome (XY) and will be a male.