Sunday, January 17, 2016

That Y-Chromosome (part 1)

All this recent DNA stuff has gotten beyond confusing.  Haplogroups, haplotypes, DYS#, locus, alleles, marker numbers, clades, subclades, mtDNA, autosomal DNA, SNPs, STPs, MVPs, MTVPs, big-Y or something like that; and on, and on, it goes.  Not too long ago, it was just the Y-chromosome, a 12-marker test, a snip or two, and off you went to that DNA sunset.

Not any more it seems.  What's one to do?  A "big" picture came to mind...that "Y-chromosome" started things off. [actually it was that mtDNA = Seven Faces of Eve... but for me things got started climbing my own family tree through the male descent].  At any rate, a "big picture" removed from all that word soup might be of help.  So here goes.

The Y-chromosome carries the linear array of genetic information essential for male sex determination.  It is the smallest of all the chromosomes.  To give you a visual picture of its related size to the other chromosomes, I have traced an image from the late prophase (a stage during its duplication phase) of a normal male karyotype. (a way the chromosomes can be visualized by their size, shape, and number)

Here you have it...the runt of the litter.  Chromosome #1 [the largest chromosome in size] is shown in comparison to the Y/X chromosome which would be numbered #23.  It only carries 78 genes, whereas the X-chromosome gene carries around 2,000 genes.  Doesn't seem fair...does it..., but its advantage is that it contains the largest "nonrecombining block" in the human genome. [nonrecombing portion of the Y-chromosome written = NRY]  In 1997, a way to detect changes [mutations] was formalized called "denaturing high-performance liquid chromatography", so off to the races it was.  The "Y Chromosomes Consortium Cell Line Repository".  The study of mutations [called polymorphisms] on the nonrecombining potion of the Y-chromosome.  Who would have guessed from the runt of the litter.

The tracing shown above is made from "figure 7-6. Karyotype of normal male, with chromosomes in late prophase" p. 278 , Nelson Textbook of Pediatrics, Behrman(Ed.), 4th Edition, Saunders....a text from my medical practice.