Males are the homogametic sex ( ZZ ), while females are the heterogametic sex ( ZW ).
2.
The homogametic sex ( females in humans ) receive two of each sex chromosome and therefore need to be homozygous to show a recessive trait.
3.
This could cause the heterogametic sex chromosome in the hybrid to be inviable or sterile, but homogametic sex chromosome will be fertile ( Futuyma 1997 ).
4.
In ZW sex-determination system used by birds the opposite is true : the male is the homogametic sex ( ZZ ), and the female is heterogametic ( ZW ).
5.
However, in birds, and some reptiles, males have two Z sex chromosomes and so are the homogametic sex, while females, with one Z and one W chromosome, are the heterogametic sex.
6.
For example, in humans, males, with an Y sex chromosome, would be referred to as the heterogametic sex, and females having two X sex chromosomes would be referred to as the "'homogametic sex " '.
7.
Regardless of their ambiguous evolutionary history, platypuses have been empirically determined to follow an XY sex-determination system, with females possessing five pairs of X chromosomes as the homogametic sex, and males possessing five X and five Y chromosomes as the heterogametic sex.
8.
If dioecious organisms are heterogametic and the gene locus is located on the X chromosome, it can be shown that if the allele frequencies are initially unequal in the two sexes [ " e . g " ., XX females and XY males, as in humans ], in the heterogametic sex chases in the homogametic sex of the previous generation, until an equilibrium is reached at the weighted average of the two initial frequencies.
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