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In this process, an X chromosome and a Y chromosome act to determine the sex of offspring, often due to genes located on the Y chromosome that code for maleness. Offspring have two sex chromosomes: an offspring with two X chromosomes (XX) will develop female characteristics, and an offspring with an X and a Y chromosome (XY) will develop male ...
The Y chromosome is one of two sex chromosomes in therian mammals and other organisms.Along with the X chromosome, it is part of the XY sex-determination system, in which the Y is the sex-determining chromosome because the presence of the Y chromosome causes offspring produced in sexual reproduction to be of male sex.
The human Y-chromosome has had about 5 strata since the origin of the X and Y chromosomes about 300 Mya from a pair of autosomes. Each stratum was formed when a pseudoautosomal region (PAR) of the Y chromosome is inverted, stopping it from recombination with the X chromosome.
Males with Klinefelter syndrome typically have one extra copy of the X chromosome in each cell, for a total of two X chromosomes and one Y chromosome (47,XXY). It is less common for affected males to have two or three extra X chromosomes (48,XXXY or 49,XXXXY) or extra copies of both the X and Y chromosomes (48,XXYY) in each cell.
The 23rd pair of chromosomes are called allosomes. These consist of two X chromosomes in females, and an X chromosome and a Y chromosome in males. Females therefore have 23 homologous chromosome pairs, while males have 22. The X and Y chromosomes have small regions of homology called pseudoautosomal regions.
In the absence of a Y chromosome, the fetus will undergo female development. This is because of the presence of the sex-determining region of the Y chromosome, also known as the SRY gene. [5] Thus, male mammals typically have an X and a Y chromosome (XY), while female mammals typically have two X chromosomes (XX).
PAR1 comprises 2.6 Mbp of the short-arm tips of both X and Y chromosomes in humans and great apes (X and Y are 154 Mbp and 62 Mbp in total). PAR2 is at the tips of the long arms, spanning 320 kbp. [5] The monotremes, including the platypus and echidna, have a multiple sex chromosome system, and consequently have 8 pseudoautosomal regions. [6]
[4] [3] The human Y chromosome, consisting of 62,460,029 base pairs from a different cell line and found in all males, was sequenced completely in January 2022. [5] The current version of the standard reference genome is called GRCh38.p14 (July 2023). It consists of 22 autosomes plus one copy of the X chromosome and one copy of the Y chromosome.