Start Lahore sex18

Lahore sex18

the origin of chromosomal sex determination may have been fairly early in eukaryotes (see Evolution of anisogamy).

XY sex determination is used by most mammals, and from a comparison between chicken and human, the Z chromosome appeared similar to the autosomal chromosome 9 in human, rather than X or Y, suggesting that the ZW and XY sex-determination systems do not share an origin, but that the sex chromosomes are derived from autosomal chromosomes of the common ancestor of birds and mammals.

A paper from 2004 compared the chicken Z chromosome with platypus X chromosomes and suggested that the two systems are related.

For instance, mate choice and sexual selection can accelerate the evolution of physical differences between the sexes.

These gametes are the cells that are prepared for the sexual reproduction of the organism.

In addition to animals, plants, and fungi, other eukaryotes (e.g.

the malaria parasite) also engage in sexual reproduction.

The gametes produced by an organism are determined by its sex: males produce male gametes (spermatozoa, or sperm, in animals; pollen in plants) while females produce female gametes (ova, or egg cells); individual organisms which produce both male and female gametes are termed hermaphroditic.