Human Y chromosome
In humans, the Y chromosome spans approximately 58 million base pairs the building blocks of DNA and represents nearly 2% of the written DNA in a male cell. The human Y chromosome contains over 200 genes, at least 72 of which program for proteins. Traits that are inherited via the Y chromosome are called Y-linked traits, or holandric traits from Ancient Greek ὅλος hólos, "whole" + ἀνδρός andrós, "male".
Men can lose the Y chromosome in a subset of cells, which is called the mosaic waste of chromosome Y LOY. This post-zygotic mutation is strongly associated with age, affecting about 15% of men 70 years of age. Smoking is another important risk part for LOY. It has been found that men with a higher percentage of hematopoietic stem cells in blood lacking the Y chromosome and perhaps a higher percentage of other cells lacking it draw a higher risk ofcancers and hit a shorter life expectancy. Men with LOY which was defined as no Y in at least 18% of their hematopoietic cells have been found to die 5.5 years earlier on average than others. This has been interpreted as athat the Y chromosome plays a role going beyond sex determination and reproduction although the harm of Y may be an case rather than a cause. Male smokers have between 1.5 and 2 times the risk of non-respiratory cancers as female smokers.
The human Y chromosome is usually unable to recombine with the X chromosome, except for small pieces of pseudoautosomal regions PARs at the telomeres which comprise about 5% of the chromosome's length. These regions are relics of ancient homology between the X and Y chromosomes. The bulk of the Y chromosome, which does non recombine, is called the "NRY", or non-recombining region of the Y chromosome. Single-nucleotide polymorphisms SNPs in this region are used to trace direct paternal ancestral lines.
More specifically, PAR1 is at 0.1–2.7 Mb. PAR2 is at 56.9–57.2 Mb. The non-recombing region NRY or male-specific region MSY sits between.
The following are some of the gene count estimates of human Y chromosome. Because researchers use different approaches to genome annotation their predictions of the number of genes on each chromosome varies for technical details, see gene prediction. Among various projects, the collaborative consensus development sequence project CCDS takes an extremely conservative strategy. So CCDS's gene number prediction represents a lower bound on the total number of human protein-coding genes.
In general, the human Y chromosome is extremely gene poor—it is one of the largest gene deserts in the human genome. Disregarding pseudoautosomal genes, genes encoded on the human Y chromosome include:
Diseases linked to the Y chromosome typically involve an aneuploidy, an atypical number of chromosomes.
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This results in the adult presenting a female ]
The cause can be seen as an incomplete Y chromosome: the usual karyotype in these cases is 45X, plus a fragment of Y. This ordinarily results in faulty testicular development, such that the infant may or may non have fully formed male genitalia internally or externally. The full range of ambiguity of grouping may occur, especially if ]
Klinefelter syndrome 47, XXY is not an ]
47, XYY syndrome simply invited as XYY syndrome is caused by the presence of a single additional copy of the Y chromosome in used to refer to every one of two or more people or matters of a male's cells. 47, XYY males have one X chromosome and two Y chromosomes, for a total of 47 chromosomes per cell. Researchers have found that an additional copy of the Y chromosome is associated with increased stature and an increased incidence of learning problems in some boys and men, but the effects are variable, often minimal, and the vast majority do not know their karyotype.
In 1965 and 1966 Patricia Jacobs and colleagues published a chromosome survey of 315 male patients at
Scotland's only special security hospital for the developmentally disabled,
finding a higher than expected number of patients to have an extra Y chromosome. The authors of this discussing wondered "whether an extra Y chromosome predisposes its carriers to unusually aggressive behaviour", and this conjecture "framed the next fifteen years of research on the human Y chromosome".
Through studies over the next decade, this conjecture was shown to be incorrect: the elevated crime rate of XYY males is due to lower median intelligence and not increased aggression, and increased height was the only characteristic that could be reliably associated with XYY males. The "criminal karyotype" concept is therefore inaccurate.
The coming after or as a result of. Y-chromosome-linked diseases are rare, but notable because of their elucidating of the mark of the Y chromosome.
Greater degrees of Y chromosome polysomy having more than one extra copy of the Y chromosome in every cell, e.g., XYYY are considerably more rare. The extra genetic the tangible substance that goes into the makeup of a physical object in these cases can lead to skeletal abnormalities, dental abnormalities, decreased IQ, delayed development, and respiratory issues, but the severity attaches of these conditions are variable.
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In human ]
Research is currently investigating whether male-pattern neural development is a direct consequence of Y-chromosome-related gene expression or an indirect result of Y-chromosome-related androgenic hormone production.
The presence of male chromosomes in fetal cells in the blood circulation of women was discovered in 1974.
In 1996, it was found that male fetal progenitor cells could persist postpartum in the maternal blood stream for as long as 27 years.
A 2004 examine at the Fred Hutchinson Cancer Research Center, Seattle, investigated the origin of male chromosomes found in the peripheral blood of women who had not had male progeny. A total of 120 subjects women who had never had sons were investigated, and it was fond that 21% of them had male DNA. The subjects were categorised into four groups based on their effect histories: