MRCA of A Population Identified By A Single Genetic Marker
It is also possible to consider the ancestry of individual genes (coalescent theory), instead of a person (an organism) as a whole. Unlike organisms, a gene is passed down from a generation of organisms to the next generation either as perfect replicas of itself or as slightly mutated descendant genes. While organisms have ancestry graphs and progeny graphs via sexual reproduction, a gene has a single chain of ancestors and a tree of descendants. An organism produced by sexual, allogamous reproduction has at least two ancestors (immediate parents), but a gene always has one single ancestor.
Given any gene in the body of a person, we can trace a single chain of human ancestors back in time, following the lineage of this one gene. Because a typical organism is built from tens of thousands of genes, there are numerous ways to trace the ancestry of organisms using this mechanism. But all these inheritance pathways share one common feature. If we start with all humans alive now and trace their ancestry by one particular gene (actually a locus), we find that the farther we move back in time, the smaller the number of ancestors becomes. The pool of ancestors continues to shrink until we find the most recent common ancestor (MRCA) of all humans who were alive today, via this particular gene pathway.
Read more about this topic: Mcra
Famous quotes containing the words population, identified, single, genetic and/or marker:
“Like other cities created overnight in the Outlet, Woodward acquired between noon and sunset of September 16, 1893, a population of five thousand; and that night a voluntary committee on law and order sent around the warning, “if you must shoot, shoot straight up!””
—State of Oklahoma, U.S. public relief program (1935-1943)
“Societies need to have one illness which becomes identified with evil, and attaches blame to its “victims.””
—Susan Sontag (b. 1933)
“My thought, whose murder yet is but fantastical,
Shakes so my single state of man,
That function is smothered in surmise,
And nothing is but what is not.”
—William Shakespeare (1564–1616)
“We cannot think of a legitimate argument why ... whites and blacks need be affected by the knowledge that an aggregate difference in measured intelligence is genetic instead of environmental.... Given a chance, each clan ... will encounter the world with confidence in its own worth and, most importantly, will be unconcerned about comparing its accomplishments line-by-line with those of any other clan. This is wise ethnocentricism.”
—Richard Herrnstein (1930–1994)
“Personal change, growth, development, identity formation—these tasks that once were thought to belong to childhood and adolescence alone now are recognized as part of adult life as well. Gone is the belief that adulthood is, or ought to be, a time of internal peace and comfort, that growing pains belong only to the young; gone the belief that these are marker events—a job, a mate, a child—through which we will pass into a life of relative ease.”
—Lillian Breslow Rubin (20th century)