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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 list of organisms by chromosome count describes ploidy or numbers of chromosomes in the cells of various plants, animals, protists, and other living organisms. This number, along with the visual appearance of the chromosome, is known as the karyotype , [ 1 ] [ 2 ] [ 3 ] and can be found by looking at the chromosomes through a microscope .
The SRY (Sex-determining Region of the Y chromosome) directs male development in mammals by inducing the somatic cells of the gonadal ridge to develop into a testis, rather than an ovary. [10] Sry is expressed in a small group of somatic cells of the gonads and influences these cells to become Sertoli cells (supporting cells in testis).
Among the six species, the Y chromosome exhibited much more variability than the X chromosome. For example, the X chromosomes of humans and chimpanzees are about 98 percent identical in makeup.
The Y-chromosome has been entirely mapped, [7] revealing many Y-linked traits. [8] Y linkage is similar to, but different from X linkage; although, both are forms of sex linkage. X linkage can be genetically linked and sex-linked, while Y linkage can only be genetically linked. This is because males' cells have only one copy of the Y-chromosome.
In humans, the SRY gene is located on short (p) arm of the Y chromosome at position 11.2. Sex-determining region Y protein (SRY), or testis-determining factor (TDF), is a DNA-binding protein (also known as gene-regulatory protein/transcription factor) encoded by the SRY gene that is responsible for the initiation of male sex determination in therian mammals (placentals and marsupials). [5]
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]