Why are male calico cats so rare?

Why do male cats have only one X chromosome?

Male cats have only one X chromosome and one Y chromosome (short, vertical grey line) and so are either all black or all orange. The gene which creates white, pigmentless patches is inherited independently of the color genes and is not located on the X chromosome.

How many X-chromosomes does a female have?

The sex-determining system of all mammals dictates that females have two X-chromosomes and males have one X- and one Y-chromosome. While the Y-chromosome contains few genes, the X-chromosome contains over one-thousand genes that are essential for proper development and cell viability.

What are some examples of X-chromosome inactivation in cats?

A prime example of X-chromosome inactivation can be found in the calico coat colour patterning exhibited in some cats. In these cats, the fur pigmentation gene is X-linked; one X-chromosome encodes an orange coat colour and the other gives a black or tabby.

What is the difference between X and Y chromosomes in mammals?

Female (XX) mammals inherit one X chromosome from each parent, but males (XY) receive an X from their mother and a Y sex chromosome from their father. X and Y chromosomes determine not only the sex of an individual, but many broad characteristics as well.

How do cells decide which X chromosome is to be inactivated?

Very early in development, cells “count” the number of X chromosomes and decide if one needs to be inactivated, and if so which one. There is a region of the X chromosome called the X inactivation center which is enriched in long non-coding RNAs (lncRNAs).

Why do female mammals undergo X chromosome inactivation?

To compensate for this genetic inequality, female mammals undergo X chromosome inactivation in which one of the X chromosomes is randomly chosen to be silenced.

What does X inactivation mean in cats?

This X-chromosome inactivation, also called X-inactivation, means that a female cat with the Oo genotype will have some cells that express the O allele (and thus grow orange fur), while other cells express the o allele and grow black/brown fur.

What is X inactivation of the X chromosome?

Inactivation of copies of X chromosome. The coloration of tortoiseshell and calico cats is a visible manifestation of X-inactivation. The black and orange alleles of a fur coloration gene reside on the X chromosome.

How is the paternal X-chromosome inactivated in mammals?

Preferential inactivation of the paternal X-chromosome occurs in both marsupials and in cell lineages that form the membranes surrounding the embryo, whereas in placental mammals either the maternally or the paternally derived X-chromosome may be inactivated in different cell lines.

What is X-inactivation in cats?

The coloration of tortoiseshell and calico cats is a visible manifestation of X-inactivation. The black and orange alleles of a fur coloration gene reside on the X chromosome.

How many chromosomes are in a cat litter?

Some species of cat such as the ocelot have only 36 chromosomes, and breeding such a cat with a cat that has 38 chromosomes will result in offspring that have 37 chromosomes. The males in the litter, however, are likely to be sterile.

How many chromosomes do cats have compared to humans?

Domestic cats have 38 chromosomes, as compared to 46 in humans. The chromosomes come in 19 matched pairs, with one of each pair coming from each parent. Some species of cat such as the ocelot have only 36 chromosomes, and breeding such a cat with a cat that has 38 chromosomes will result in offspring that have 37 chromosomes.

How many chromosomes are in a human cell?

Most human cells contain 23 pairs of chromosomes. One set of chromosomes comes from the mother, while the other comes from the father. The twenty-third pair is the sex chromosomes, while the rest of the 22 pairs are called autosomes.

What would happen if the X chromosome is inactivated?

As shown on the illustration below, if the X chromosome carrying the gene for black fur gets inactivated, that cell will instead create orange fur. If the X chromosome carrying the gene for orange fur is inactivated, that cell will create black fur.

What is X inactivation?

Another term for X inactivation is Lyonization. This post contains excerpts from Chapter 4 of our upcoming book Embyrogenesis Explained. Figure Caption: The calico cat is a female cat with white underparts. The gene for color is located on the X chromosome (vertical line with circle under a cat).

What is X-inactivation of the X chromosome?

The inactive X chromosome is silenced by it being packaged into a transcriptionally inactive structure called heterochromatin. As nearly all female mammals have two X chromosomes, X-inactivation prevents them from having twice as many X chromosome gene products as males, who only possess a single copy of the X chromosome (see dosage compensation ).

What is an example of X inactivation in cats?

Figure 1. Tortoiseshell cat A nice example of X inactivation can be observed in the fur of tortoiseshell and calico cats. The gene for fur coloration resides on the X chromosome, while each of the two X chromosomes codes for a different colour: black or orange.

Why do female mammals have two X chromosomes?

Genetically male mammals have an X and a Y chromosome while genetically female mammals have two X chromosomes. The X chromosome is many times larger than the Y chromosome. To compensate for this genetic inequality, female mammals undergo X chromosome inactivation in which one of the X chromosomes is randomly chosen to be silenced.

Why is the X chromosome inactivated in human females?

Since human (and mammal) females have two X chromosomes, inactivation prevents them from having twice as many X chromosome gene products as males, who only possess a single copy of the X chromosome. This called dose compensation. Which X will be inactivated is random.

How is the inactivated state of an X chromosome transmitted?

The inactivated state of this X chromosome is transmitted to all copies of that chromosome during subsequent cell divisions and their mitoses.

What is the difference between the inactive X and Xa chromosomes?

The inactive X chromosome is coated by Xist RNA, whereas the Xa is not (See Figure to the right). X chromosomes that lack the Xist gene cannot be inactivated.

Why are two X chromosomes shut down in human females?

Two X chromosomes is one too many and so one has to be shut down in order (presumably) to keep gene dosage at the same level as that in the male. Very early in embryogenesis, when a female mammalian embryo is a small ball of cells, one X chromosome is inactivated in each cell.

What happens if a cat has X-inactivation?

If X-inactivation happens during this process then the cat will end up with 10 patches of colour, 5 red and 5 black, each of them derived from those initial cells.