Please help with this genetics question: While examining a young tortoiseshell c
ID: 56342 • Letter: P
Question
Please help with this genetics question:
While examining a young tortoiseshell cat, you and the vet you are interning with get a surprise- the cat is male, not female! From your undergrad genetics course, you recall that tortoiseshell coats are produced bt the random X-inactivation that takes place in mammilain females. The vet orders a chromosome analysis of the cat and finds that he is XXY: he has two X chromosomes and one Y chromosome. Help the vet figure out how a tortoiseshell cat could be male. (Hint: Think about X-inactivation in mammals with two X chromosomes)
Explanation / Answer
In mammals X-inactivation is nothing but one of the X chromosome in the female is inactivated. It is also called as lyonization. The inactivation is random and inactivation in all descendent cells.
In cats generally the coat colour is determined by X Chromosomes. The gene has two alles (Orange and Black). Due to the X-inactivation in female only one X chromosome will express one colour (Orange or Black).
In males only one X and one Y- Chromosome is present. the X chromosome does not under go X-inactivation. So coat colour is determined by any one allele present in the X- chromosome because Y- does not code any colour. So there is no chance in male to get both colours.
In rare cases a tortoiseshell male have two X chromosomes and one Y chromosome (XXY) like Klinefelter syndrome (XXY) in humans. And the cells go under X-inactivation. If this is haappens, each cell in the male embryo will undergo Lyonization, just like the female. If the two X chromosomes do not carry the same allele that is the genotype orange and black, then the male will express calico coloration, just like female.