Interspecific crosses are rare in nature and intergeneric crosses almost unknown. Why?

In inter-specific crossing the mating between the male and female of two different related species takes place. The progeny formed from such cross is generally infertile. Hence, inter-specific cross are rare in nature.

In inter-generic crossing, the crossing or mating is done between male and female of two different genus. It is completely impossible because different genus have different characters and the breeding cannot be done between two different genus.

For example: A cat cannot mate with a horse. The gametes of genus have different specificity and hence cannot be fused.

So, the inter-generic crosses are almost unknown in nature.