Is not considered separate species because organisms of different breeds
can mate and produce fertile offspring.
breed
phenotype
genotype
fitness

Breed is not considered separate species because organisms of different breeds  can mate and produce fertile offspring.

Explanation:

A breed is a particular gathering of residential creatures having homogeneous appearance (phenotype), homogeneous conduct, and additionally different attributes that recognize it from different life forms of similar species. Comprehensively, various species can't interbreed and create solid, ripe posterity because of hindrances called systems of regenerative confinement.

These obstructions can be part into two classifications dependent on when they act: prezygotic and postzygotic. Generally, various species don't mate. Be that as it may, when they do, their posterity will be what are called cross breeds.

the unequal cytoplasmic division that  results  in  one egg  and three polar bodies ensures that a fertilized  egg has  ample nutrients  forits journey  to  the uterus.