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In the XY sex-determination system, the female-provided ovum contributes an X chromosome and the male-provided sperm contributes either an X chromosome or a Y chromosome, resulting in female (XX) or male (XY) offspring, respectively.
In placental mammals, the presence of a Y chromosome determines sex. Normally, cells from females contain two X chromosomes, and cells from males contain an X and a Y chromosome.
Genes on the sex chromosomes can be expressed differently between males and females because of the presence of either single or double copies of the gene and because of the phenomena of different meiotic effects, X inactivation, and genetic imprinting.
30 sie 2016 · Using computer simulations, Page’s team has identified 639 genes that existed on the autosomal ancestor of the X and Y chromosomes humans shared with birds 300 million years ago. Today, the human X chromosome retains 629 of these ancestral genes.
In this system, referred to as the XX-XY system, maleness is determined by sperm cells that carry the Y chromosome.
Some well-known human genes on the X chromosome are the following: Red-Green color blindness, due to missing or mutated genes for one of the two-color receptor proteins on the X chromosome. A third gene, for the blue color receptor protein, is located on chromosome 7 in humans.
13 gru 2023 · The human X and Y chromosomes evolved from ordinary autosomes over the course of the last 200 million years. 1,2 Today, these homologous chromosomes—typically two X chromosomes in females, and one X and one Y chromosome in males—comprise the oldest, most massive variation in the human genome.
