Why are Tortoiseshell cats nearly alwas females? Why occasionally we see a male tortoiseshell cats?

The tortoiseshell, or calico cat, gets its coloring from a combination of specific traits. These traits occur primarily in female cats. :)

It is to do with gene expression linked to the X chromasomes. The femal cat inheriates two colour alleles dominant ginger on one X chromasome and recessive black on the other. However both X chromasomes are not active in the same cell as if they were they would get an unbalance of gene expression compaired to males who only have one. This is gene dosage. So one X chromasome is inactivated (it forms a barr body) so only genes from on is expressed. As skin cells a are clonal in origin (many divide from one) you get patches as the X chromasome expression is inherited. This causes the patchy orange and black that is tortoishell.

Males can only have orange or black as the only have one X chromasome. Males with a tortoisheoll pattern are either XXY (Klienfelter's syndrome) or caused by the fusion of embryos in the womb - genetic chimeras.

we very often see, a female tortoise shelled cat and very less a male cat with this condition. The answer to this is that... skin pattern in cats is an X linked trait. The sex determination in cats are the same as in humans.XX for females and XY for males. Now when this trait becomes expressed in males these males are infertile and thereforw do not pass there traits to the next generation.therefore you would rarelt see male cats tortoise shelled,usually male cats got plain coats and they are fertile in this condition.