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This XXY chromosome arrangement is one of the most common genetic variations from the XY karyotype, occurring in approximately one in 500 live male births. [4] [13] [36] In mammals with more than one X chromosome, the genes on all but one X chromosome are not expressed; this is known as X inactivation. This happens in XXY males, as well as ...
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). Chromosomal sex is determined ...
A mechanism of sex determination that depends upon the ratio of the number of X chromosomes (X) to the number of sets of autosomes (A). Males develop when the X/A ratio is 0.5 or less, females when it is 1.0 or more, and an intersex develops when it is between 0.5 and 1.0. [8] genic selection
Paternally-derived chromosome rearrangement psu dic: pseudo dicentric – only one centromere in a dicentric chromosome is active q: Long arm of a chromosome r: Ring chromosome t: Translocation: ter: Terminal end of arm (e.g. 2qter refers to the end of the long arm of chromosome 2) tri: Trisomy: trp: Triplication of a portion of a chromosome
While all human chromosomes contain repeats, more than 30 million letters of the Y chromosome — out of 62.5 million — are repetitive sequences, sometimes called satellite DNA or junk DNA.
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]
Females therefore have 23 homologous chromosome pairs, while males have 22. The X and Y chromosomes have small regions of homology called pseudoautosomal regions. An X chromosome is always present as the 23rd chromosome in the ovum, while either an X or Y chromosome may be present in an individual sperm. [4]
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. Hormone levels in the male parent affect the sex ratio of sperm in humans. [25]