Pseudo autosomal genes |Structure of Y chromosome | Genetics |BS Zoology

In this video we discussed about
the sequencing of the platypus genome,has suggested that the XY system would not have been present more than 166 million years ago

30.   Over time, the Y chromosome changed in such a way as to inhibit the areas around the sex determining genes(SRY) from recombining at all with the X chromosome. As a result of this process, 95% of the human Y chromosome is unable to recombine The tips of the Y chromosome that could recombine with the X chromosome are referred to as the pseudoautosomal region.

31.

32.  By one estimate, the human Y chromosome has lost 1,393 of its1,438 original genes over the course of its existence, and linear extrapolation of this 1,393 gene loss over 300 million years gives a rate of genetic loss of 4.6 genes per million years. Continued loss of genes at the 4.6 genes per million year rate would result in a Y chromosome with no functional genes that is the Y chromosome would lose complete function within the next 10 million years. Comparative genomic analysis, however, reveals that many mammalian species

33.  The Y chromosome is passed exclusively through sperm, which undergo multiple cell divisions during gametogenesis. Each cellular division provides further opportunity to accumulate base pair mutations. Additionally, sperm are stored in the highly oxidative environment of the testis, which encourages further mutation. These two conditions combined put the Y chromosome at a greater risk of mutation than the rest of the genome

34.   Without the ability to recombine during meiosis, the Y chromosome is unable to expose individual alleles to natural selection. Deleterious alleles are allowed to "hitchhike" with beneficial neighbors, thus propagating maladapted alleles in to the next generation. Conversely, advantageous alleles may be selected against if they are surrounded by harmful alleles (background selection). Due to this inability to sort through its gene content, the Y chromosome is particularly prone to the accumulation of "junk" DNA. Massive accumulations of retrotransposable elements are scattered throughout the Y.[10] The random insertion of DNA segments often disrupts encoded gene sequences and renders them nonfunctional. However, the Y chromosome has no way of weeding out these "jumping genes". Without the ability to isolate alleles, selection cannot effectively act upon them. A clear, quantitative indication of this inefficiency is the entropy rate of the Y chromosome. Whereas all other chromosomes in the human genome have entropy rates of 1.5–1.9 bits per nucleotide (compared to the theoretical maximum of exactly 2 for no redundancy), the Y chromosome's entropy rate is only 0.84.[18] This means the Y chromosome has a much lower information content relative to its overall length; it is more redundant.

35.  Even if a well adapted Y chromosome manages to maintain genetic activity by avoiding mutation accumulation, there is no guarantee it will be passed down to the next generation. The population size of the Y chromosome is inherently limited to 1/4 that of autosomes: diploid organisms contain two copies of autosomal chromosomes while only half the population contains 1 Y chromosome. Thus, genetic drift is an exceptionally strong force acting upon the Y chromosome

#biology #inheritance #chromosome #zoology #genetics

Видео Pseudo autosomal genes |Structure of Y chromosome | Genetics |BS Zoology канала Comicblast486