Vicoso B, Kaiser VB, Bachtrog D Sex-biased gene expression at homomorphic sex chromosomes in emus and its implication for sex chromosome evolution. Genotypic versus environmental sex determination With genotypic sex determination GSDwhich occurs in the majority of species with known sex-determining mechanisms, genetic elements specify whether individuals are female or male.
Anisogamy small male and large female gametes evolved independently in many eukaryotic lineages, including several different groups of protists such as red algae, brown algae, apicomplexa, dinoflagellates, and ciliates; reversed sex chromosomes determine in Washingtonas well as most plants and animals.
Separate sexes reversed sex chromosomes determine in Washington evolve from hermaphrodites either by gradual increases in sex-specific investment or rapidly by the appearance of male- or female-sterility mutations Figure 2. Sex determination in multicellular organisms and protistan mating types.
Figure 3. The transition towards anisogamy is thought to result from disruptive selection  : given opposing pressures to simultaneously maximize the number of gametes, their encounter rate, as well as the mass and ensuing survival of resulting zygotes, the fitness of both partners is often maximized when one interacting gamete is small and mobile, while its large and sessile reversed sex chromosomes determine in Washington provides the resources required for zygote development.
Hopes for future fetal biological system analysis include complete-reproduction-system initialized signals that can be measured during reversed sex chromosomes determine in Washington to more accurately determine whether a determined sex of a fetus is male, or female.
Such analysis of biological systems could also signal whether the fetus is hermaphrodite, which includes total or partial of both male and female reproduction organs. Main article: XY sex-determination system. The females are XX and produce egg cells that contain an X chromosome. Sexual differentiation humans Development of the reproductive system gonads Mesonephric duct Paramesonephric duct.
A sex chromosomealso referred to as reversed sex chromosomes determine in Washington allosomeheterotypical chromosomeor heterochromosome  or idiochromosome  is a chromosome that differs from an ordinary autosome in form, size, and behavior.
New York: Penguin.
Dataset 3. Vertebrates: Mammalia placental, marsupial, and monotreme mammals , Aves birds , Reptilia turtles, snakes, crocodiles, lizards , Amphibia frogs, toads, salamanders , and Teleostei bony fishes. Heredity — Sex determination can also differ with respect to where in the body sex is determined.
Sexual reproduction: the mixing of genomes via meiosis and fusion of gametes.