justinacolmena
Gold Member
- Banned
- #1
The superclass Tetrapoda consists of the classes Amphibia, Reptilia, Aves, and Mammalia.
Among mammals, biological sex is determined by a pair of chromosomes, XX for female and XY for male. The female among mammals is said to be the homozygous sex and the male to be the heterozygous sex.
Among birds, there is a different pair of chromosomes that determines sex in a manner not analogous to that of mammals. Namely male birds have a ZZ pair of chromosomes and females ZW. Thus among birds, the male is the homozygous sex and the female is the heterozygous sex, conversely to mammals.
Among reptiles sex is determined among a cluster of eggs in such a manner that the cooler ones develop into males, and the warmer ones develop into females. Occasionally female reptiles of certain species are able to reproduce by "cloning themselves" without being impregnated by a male.
The temperature dependence of sex selection among reptiles is preserved in mammals, where the testicles must be kept at a lower temperature for the development of spermatozoa and the ovaries at a higher temperature in the core of the body especially during œstrus or ovulation when the temperature of a female body must increase above normal for menstruation.
Amphibians have various sex selection mechanisms I have not studied. These are rougher divided into the Anura, frogs and toads which lack tails as adults, and various types of salamanders which have a lizard-like body form although they are not true reptiles.
Various sorts of fishes have still other sex selection mechanisms.
Among mammals, biological sex is determined by a pair of chromosomes, XX for female and XY for male. The female among mammals is said to be the homozygous sex and the male to be the heterozygous sex.
Among birds, there is a different pair of chromosomes that determines sex in a manner not analogous to that of mammals. Namely male birds have a ZZ pair of chromosomes and females ZW. Thus among birds, the male is the homozygous sex and the female is the heterozygous sex, conversely to mammals.
Among reptiles sex is determined among a cluster of eggs in such a manner that the cooler ones develop into males, and the warmer ones develop into females. Occasionally female reptiles of certain species are able to reproduce by "cloning themselves" without being impregnated by a male.
The temperature dependence of sex selection among reptiles is preserved in mammals, where the testicles must be kept at a lower temperature for the development of spermatozoa and the ovaries at a higher temperature in the core of the body especially during œstrus or ovulation when the temperature of a female body must increase above normal for menstruation.
Amphibians have various sex selection mechanisms I have not studied. These are rougher divided into the Anura, frogs and toads which lack tails as adults, and various types of salamanders which have a lizard-like body form although they are not true reptiles.
Various sorts of fishes have still other sex selection mechanisms.
