From: "Helen Grierson" <grierson@mitec.net> To: OHBROWN-L@rootsweb.com Date: Thu, 7 Dec 2000 00:02:30 -0600 Subject: [OHBROWN] DNA and other factors Message-ID: <005101c06013$5a3d8440$404e84d0@a0g5u9> Received: from mx6.boston.juno.com (mx6.boston.juno.com [63.211.172.38]) by m12.boston.juno.com with SMTP id AAA7C9LCVAC4U7WA for <hermfagley@juno.com> (sender <OHBROWN-L-request@rootsweb.com>); Thu, 7 Dec 2000 10:10:11 -0500 (EST) Received: from lists6.rootsweb.com (lists6.rootsweb.com [63.92.80.125]) by mx6.boston.juno.com with SMTP id AAA7C9LCUA2JVLGA (sender <OHBROWN-L-request@rootsweb.com>); Thu, 7 Dec 2000 10:10:10 -0500 (EST) Received: (from slist@localhost) by lists6.rootsweb.com (8.10.1/8.10.1) id eB7F58K04865; Thu, 7 Dec 2000 07:05:08 -0800 X-Mailer: Microsoft Outlook Express 5.00.2615.200 MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" X-Status: Read X-Juno-Att: 0 Precedence: list X-Original-Sender: grierson@mitec.net Thu Dec 7 07:05:08 2000 X-Priority: 3 Old-To: <OHBROWN-L@rootsweb.com> X-MSMail-Priority: Normal Resent-Message-ID: <9Pr5hB.A.1LB.kc6L6@lists6.rootsweb.com> Return-Path: <OHBROWN-L-request@rootsweb.com> Resent-Sender: OHBROWN-L-request@rootsweb.com X-Mailing-List: <OHBROWN-L@rootsweb.com> archive/latest/1243 Resent-From: OHBROWN-L@rootsweb.com X-Loop: OHBROWN-L@rootsweb.com X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2615.200 Resent-Date: Thu, 7 Dec 2000 07:05:08 -0800 A chicken's egg is a type of cell - it is an egg cell, similar to a human female egg cell. If a human egg is fertilized by a male sperm, the fertilized egg develops into a new human. The "white" of the egg is the cytoplasm, the "yellow" is the nucleus. Mitochondria, which contain among other things mitochondrial DNA, are small structures located in the cytoplasm of all cells in the body. They are called the powerhouses of the cell, and help provide energy for cells to function. Mitochondrial DNA contains structures called "genes" (where the term genetics comes from), which provide instructions to the mitochondria. The nucleus also contains DNA, which is made up of genes. In humans, all cells in the body except eggs and sperm, have their nuclear genes located on 46 strands of DNA called chromosomes. Actually, there are 2 sets of 23 chromosomes, one set which came from Mom, and one set which came from Dad. 22 pairs of the chromosomes are alike, and the 23rd pair are different - they are called the "sex chromosomes" ("X" or "Y"). The egg contains one set of chromosomes, the sperm contains another set, and when the egg is fertilized, the new person then has a full set of 23 pairs once again. All body cells (except the egg and sperm) of a human female have 2 "X" chromomes, and all body cells of human male have 1 "X" and 1 "Y". When egg and sperm cells are formed in Mom and Dad, the 2 sets of chromosomes are separated, so each egg and each sperm has only one of each type, including the sex chromomes. Females make only eggs with X chromosomes, and males make sperm with both X and Y chromosomes. If a sperm with an X fertilizes an egg, a new female results, if a sperm with a Y fertilizes the egg, the baby will be a boy. So the male determines the sex of the child. Back to mitochondrial DNA: The egg has both cytoplasm and a nucleus; the sperm which fertilizes the egg is mostly DNA, and only enough mitochondria go provide power for the trip to the egg. So, after fertilization, all cells of the new person will have mitochondrial DNA which came entirely from the Mom (who got it from her mother, who got it from her mother - and on and on back to the beginning). When we talk about inheritance, we are talking mainly about the other DNA, in the nucleus. Each chromosome of each pair is made up of structures called genes, which contain instructions for everything our body is and does! For example, there is a gene which determines our eye color, another which controls our hair color, another which regulates our immune system. There are over 1million known pairs of genes located on the 23 pairs of chromosomes. Only 1 of each pair of genes functions in each cell in the body, so if you have one gene which is "bad", or defective, you still have another one which can work. The sex chromosomes are different, because the X chromosome is bigger, and contains more, and different genes from the Y chromosome. In the case of families with immune-deficiency disease like SCID, the gene causing the problem is located on the X chromosome, and the females carry, or transmit, the disease, but don't get sick because they also have a normal gene to cancel out the bad gene. Boys inherit their X chromosome from their mother; if the X is normal, they are ok, but if the X is defective, they get the disease. Because the mother has 2 types of eggs (one with the good X and 1 with the bad X), there is a 1 in 2, or 50% chance that the sperm will fertilize a bad egg, and the boy will be affected. If these parents had 100 children, 50 boys and 50 girls, 25 boys will be OK, 25 will be affected, 25 girls will be "carriers", and 25 girls will not be carriers. Helen