During evolution different species lineages came into existence due to the presence of zygotic barriers. These zygotic barriers can be classed into two categories: prezygotic and postzygotic barriers. Prezygotic barriers are physical isolation, behavioural isolation, temporal isolation, and at the point of mating there is mechanical and gametic isolation. Postzygotic barriers are present after fertilisation and include reduced hybrid viability, reduced hybrid fertility and hybrid breakdown (Campbell & Reece, 2002). Generally hybrids are described as infertile, with the text book example being the mule which is a cross of a horse and a donkey where the two species have a chromosome number difference. This rule of infertile offspring between species as previously discussed does no hold true for all cases. Fitzpatrick & Shaffer (2007) compared the hybrid larvae in native California Tiger Salamanders (Ambystoma californiense) which are protected under the U.S. Endangered Species Act and in
2007-11-04
15:43:53
·
2 answers
·
asked by
vivien h
3