The sex we're assigned at birth depends largely on a genetic flip of the coin: X or Y? Two X chromosomes and you almost always develop ovaries. An X and a Y chromosome? These packages of genetic material don't just differ in terms of the body parts they give us.
Study Says Oldest Known Human Y-Chromosome Branch Dates to 338,000 Years Ago
Evaluating the Y chromosomal timescale in human demographic and lineage dating
In human genetics , the Y-chromosomal most recent common ancestor Y-MRCA , informally known as Y-chromosomal Adam is the most recent common ancestor MRCA from whom all currently living males are descended patrilineally. The term Y-MRCA reflects the fact that the Y chromosomes of all currently living human males are directly derived from the Y chromosome of this remote ancestor. The analogous concept of the matrilineal most recent common ancestor is known as " Mitochondrial Eve " mt-MRCA, named for the matrilineal transmission of mtDNA , the most recent woman from whom all living humans are descended matrilineally. As with "Mitochondrial Eve", the title of "Y-chromosomal Adam" is not permanently fixed to a single individual, but can advance over the course of human history as paternal lineages become extinct.
Evaluating the Y chromosomal timescale in human demographic and lineage dating
Y chromosome is a superb tool for inferring human evolution and recent demographic history from a paternal perspective. However, Y chromosomal substitution rates obtained using different modes of calibration vary considerably, and have produced disparate reconstructions of human history. Here, we discuss how substitution rate and date estimates are affected by the choice of different calibration points. We argue that most Y chromosomal substitution rates calculated to date have shortcomings, including a reliance on the ambiguous human-chimpanzee divergence time, insufficient sampling of deep-rooting pedigrees, and using inappropriate founding migrations, although the rates obtained from a single pedigree or calibrated with the peopling of the Americas seem plausible. We highlight the need for using more deep-rooting pedigrees and ancient genomes with reliable dates to improve the rate estimation.

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