From SIB@ECL.PSU.EDU Fri Oct 22 13:44:23 1993 Path: doc.ic.ac.uk!agate!howland.reston.ans.net!paladin.american.edu!auvm!ECL.PSU.EDU!SIB Comments: Gated by NETNEWS@AUVM.AMERICAN.EDU Newsgroups: soc.roots Return-Path: <@AUVM.AMERICAN.EDU,@VTBIT.CC.VT.EDU:owner-roots-l@VM1.NODAK.EDU> Return-Path: <@VM1.NODAK.EDU:SIB@ECL.PSU.EDU> X-VMS-To: ROOTS-L@VM1.NODAK.EDU MIME-version: 1.0 Content-type: TEXT/PLAIN; CHARSET=US-ASCII Content-transfer-encoding: 7BIT Message-ID: <01H4BB3DJ48I8WXCO4@ecl.psu.edu> Date: Tue, 19 Oct 1993 23:28:55 -0400 Reply-To: SIB@ECL.PSU.EDU Sender: ROOTS-L Genealogy List From: SIB@ECL.PSU.EDU Subject: Y-chromosome question Comments: To: ROOTS-L@VM1.NODAK.EDU Lines: 55 Tim Gaus asked two questions: first, is a man's Y chromosome identical to that of his paternal line ancestors?; second, does the Y chromosome DO anything other than determine the sex of the individual? Here are the short answers. 1) No, a man shares only a part (about half) of his non-standard Y-chromosome information with his father. (Note that most genetic information encoded into our DNA does not vary between any two people, and in fact is largely identical to the DNA of, say, hamsters.) 2) Yes, the Y chromosome contains information on many aspects of a man's body, only one of which is his sex. Here's a *VERY* short course on chromosomes, open to correction by geneticists or anyone else who knows more than I do. We have 23 pairs of chromosomes in each of our cells. In each pair, we get one from Dad and one >from Mom. We number the pairs of chromosomes by size, with the biggest pair being called "one", the next biggest called "two", and so on until we get to the smallest pair, called "22". The 23rd pair is specially reserved, and is called the "sex chromosome" pair. All chromosomes have four arms radiating out >from a central point, which makes them look like an X. However, in the male, one of the two 23rd chromosomes has a very short arm, which makes it look like a Y instead of an X. Thus, the male's two sex chromosomes look like an X and a Y, while the female's look like two Xs. In the gonads of each mature individual, the two chromosomes in each pair engage in an important activity called "crossing over". In this, a part of a chromosome arm breaks off and trades places with the same part in its sister chromosome. This is repeated a very large number of times, with the result that the genetic information on each chromosome is essentially "shuffled". Then, when the sperm or ovum is formed, the chromosome pairs each split so that each sperm or ovum has only ONE of each chromosome. This set of single chromosomes then combines with the other single set of chromosomes in the other gamete (sperm or ovum) to form a pair of each chromosome again. Thus, only HALF of our genetic information is passed onto our children, with the other half given by our spouse. Note that the Y chromosome that I gave to my son contained information >from both my Y chromosome and also my X chromosome, due to crossing over. Therefore, he got roughly equal amounts of inherited characteristics from my father and my mother (his paternal grandparents). If we don't count mitochondrial DNA, he also got the same amount from his maternal grandparents. Great how that works out, isn't it? One last thing. Geneticists and genealogists are sometimes interested in tracing "sex-linked" characteristics across generations. Here's an example. The gene that controls color vision is located on the 23rd X chromosome. This gene sometimes produces a colorblind eye. How does a man end up colorblind? Well, he doesn't get a 23rd X chromosome from his father, so a man can ONLY be colorblind if his MOTHER carries that gene in at least one of her 23rd X chromosomes. (Notice that, if the gene on her other 23rd X chromosome is normal, the mother WILL NOT be colorblind -- just a "carrier".) Since a man has only one 23rd X chromosome, if he gets the "colorblind" gene from his mother, he will be colorblind. How does a woman end up colorblind? Since she gets a 23rd X chromosome from BOTH her father and her mother, they must EACH give her a "colorblind" gene on their 23rd X chromosome. That means that the father MUST be colorblind, and the mother must at least be a carrier. This is why men are colorblind so much more often than women. OK, too long. Sorry. This stuff is just so neat that I want everyone to know it, so that they can appreciate it, too. Stephen Beecroft sib@eclx.psu.edu From clark@biodec (Bob Clark) Fri Oct 22 13:50:27 1993 Newsgroups: soc.roots Path: doc.ic.ac.uk!pipex!howland.reston.ans.net!spool.mu.edu!uwm.edu!wupost!eclnews!biodec!clark From: clark@biodec (Bob Clark) Subject: Re: Thanks for "Genealogy/DNA" Message-ID: <1993Oct21.011128.20699@wuecl.wustl.edu> Sender: usenet@wuecl.wustl.edu (News Administrator) Organization: Washington University, School of Engineering, St. Louis MO X-Newsreader: TIN [version 1.2 PL0] References: <01H4APCGOM8O9BWDNW@vms.cis.pitt.edu> Date: Thu, 21 Oct 1993 01:11:28 GMT Lines: 35 Timothy Gaus (TGAUS@VMS.CIS.PITT.EDU) wrote: : Thanks to everyone who submitted their expertise on my question about : genealogy and DNA. It was overwhelming but fascinating nevertheless. If : I can add just one more query - Would the Y chromosome of any male : child be exactly the same, gene for gene, as those of his male ancestors? : I wasn't clear on this point, also on whether the Y chromosome is responsible : for doing anything else except determining that its recipient will be : male. I'll not ask anymore questions on this subject so as not to : crowd out the more genealogy-specific questions, but thanks again! As to your query whether the Y chromosome would be "exactly" the same as those of all male ancestors, for the most part this would be true except for a region at the telomere (end) of the Y chromosome called the pseudoautosomal region. This region shares homology to the X chromosome, and thereby shows quite a bit of crossover with the X chromosome. Thus this region can change from male to male. As to other genes on the Y chromosome other than that gene that controls "maleness" (the TDF (testis determining factor gene)), the Y chromosome is for the most part "inactive" with the great majority of the chromosome existing as heterochomatin (generally inactive region). However, the Y chromosome, especially in the pseudoautosomal region, has at least 10 known genes..i'm sure more will be found soon. Robert Clark Dept. of Psychiatry Washington University School of Medicine clark@biodec.wustl.edu Researching JENNINGS, RANDALL, DAVIS, HAWLEY, PAUL, & FULTON (NJ) C Washington : Tim Gaus : TGAUS@vms.cis.pitt.edu : Researching GAUS, YAMAN, MAROLD, KOLLING, EVANS (in PA), SAAR From Elizabeth Harris Mon Oct 25 12:26:07 1993 Path: doc.ic.ac.uk!uknet!pipex!howland.reston.ans.net!paladin.american.edu!auvm!HERCULES.ACPUB.DUKE.EDU!chlamy Comments: Gated by NETNEWS@AUVM.AMERICAN.EDU Newsgroups: soc.roots Return-Path: <@AUVM.AMERICAN.EDU,@VTBIT.CC.VT.EDU:owner-roots-l@VM1.NODAK.EDU> Return-Path: <@VM1.NODAK.EDU:chlamy@HERCULES.ACPUB.DUKE.EDU> Message-ID: <9310221255.AA05208@raphael.acpub.duke.edu> Date: Fri, 22 Oct 1993 08:58:43 -0500 Reply-To: chlamy@HERCULES.ACPUB.DUKE.EDU Sender: ROOTS-L Genealogy List From: Elizabeth Harris Subject: Re: DNA info correction Comments: To: ROOTS-L@VM1.NoDak.EDU Comments: cc: SIB@ECLX.PSU.EDU Lines: 80 Replying to a post by Stephen Beecroft: >> I liked your post and have the smallest possible nit picking. I believe >>that the chromosomes look like they have 4 arms as they are separating >>and so it is the pair still attached that that has the 4 arms. > >Hmmm. Not so small a correction, I'd say. Furthermore, come to think of it, >I think he's right! (This is why I'm not a geneticist.) Can anyone cnfirm >that, indeed, a chromosome has four arms only when about to divide? > Simple answer: yes, you only see four arms in the early stages of cell division. More complicated answer: In non-dividing cells, the chromosomes are in an "uncondensed" state and are not visible as separate entities. DNA replication occurs during this time. As division begins, the chromosomes condense and coil up, becoming visible with a microscope. What you see as four strands are in fact the duplicated chromosomes, called "sister chromatids", which are connected by a special structure called the centromere. In mitosis (the cell division that occurs in body cells) the chromosomes line up at the center of the cell, and then separate at the centromeres, with one sister chromatid of each pair going to each daughter cell to become the new chromosome there. Every daughter cell gets exactly the same chromosome set as was present in the starting cell. In meiosis (the specialized cell division that produces egg and sperm cells, and thus the relevant process for genealogy), two division steps have to occur, in order to reduce the chromosome complement in each egg and sperm cell to one of each chromosome. (That way the embryo gets back to a complete set, with two of each chromosome, one from the egg and one from the sperm). Like mitosis, meiosis starts with chromosome condensation, but then the pairs of chromosomes that originated from each parent (i.e. your mother's copy of chromosome I and your father's copy of the same chromosome) associate with one another, and recombination can occur between matching segments of each, leading to the mixture of parental genes that we've already discussed earlier this week. Because one duplicated arm may recombine with its equivalent from the other parent, while its duplicate does not, you can (and do) end up with each of the four recombined arms having a different set of parental genes. Now comes the tricky part: The first cell division occurs, but each recombined chromosome, appearing to be four arms connected at a single central point (the centromere), stays together, i.e. the centromeres don't divide. Then a second cell division occurs which separates these arms at the centromere, and one sister chromatid goes to each daughter cell. The net result is that you get four new cells, each containing one chromosome, and, because of those recombination events, all four cells have a different combination of the parental genes. For example, suppose you got genes A and B from your mother and corresponding genes a and b from your father, and that these genes are linked, i.e. on the same chromosome. After recombination and the completion of meiosis, you might have four cells with the following gene composition: A B, A b, a B, a b i.e. one looks like your mother, one looks like your father, and the other two are recombinant; all four are different. Your child will get one of these chromosomes, and an equivalent chromosome from your spouse. Multiply this recombination and reassortment process by thousands of genes, and you get an idea of the diversity that can be achieved. Incidentally, all four meiotic products in a mammalian male cell can become sperm cells, but in formation of the egg, the cells divide asymmetrically in each division so that only one big egg cell is formed, together with some tiny cells called polar bodies. I tried to draw this all out for you, but it doesn't lend itself well to ascii characters in e-mail. Borrow your kid's or a neighbor's high school biology textbook for a good diagram! Elizabeth Harris chlamy@acpub.duke.edu