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Y-linked inheritance Pedigree tree showing the inheritance of a Y-linked trait. Y linkage, also known as holandric inheritance (from Ancient Greek ὅλος hólos, "whole" + ἀνδρός andrós, "male"), [1] describes traits that are produced by genes located on the Y chromosome. It is a form of sex linkage. Y linkage can be difficult to detect.
The human Y chromosome is composed of about 62 million base pairs of DNA, making it similar in size to chromosome 19 and represents almost 2% of the total DNA in a male cell. [54] [55] The human Y chromosome carries 693 genes, 107 of which are protein-coding. [56]
There are many more X-linked conditions than Y-linked conditions, since humans have several times as many genes on the X chromosome than the Y chromosome. Only females are able to be carriers for X-linked conditions; males will always be affected by any X-linked condition, since they have no second X chromosome with a healthy copy of the gene.
Since 2010, scientists have known that the Y chromosome is rapidly evolving in humans, but a new study shows that the same can be said across all Great Apes—the closest relatives to humans.
There are two kinds of sex chromosomes–X and Y. In humans and in almost all other mammals, females carry two X chromosomes, designated XX, and males carry one X and one Y, designated XY. [1] A human egg contains only one set of chromosomes (23) and is a haploid. Sperm also have only one set of 23 chromosomes and are therefore haploid.
Genetic linkage is the tendency of DNA sequences that are close together on a chromosome to be inherited together during the meiosis phase of sexual reproduction.Two genetic markers that are physically near to each other are unlikely to be separated onto different chromatids during chromosomal crossover, and are therefore said to be more linked than markers that are far apart.
The SHOX gene in the PAR1 region is the gene most commonly associated with and well understood with regards to disorders in humans, [17] but all pseudoautosomal genes escape X-inactivation and are therefore candidates for having gene dosage effects in sex chromosome aneuploidy conditions (45,X, 47,XXX, 47,XXY, 47,XYY, etc.).
Analysis of the Y chromosome is one of the methods used in tracing the history of early humans. Thirteen genetic markers on the Y-chromosome differentiate populations of human beings. It is believed, on the basis of genetic evidence, that all human beings in existence now descend from one single man who lived in Africa about 60,000 years ago. [2]