The child since they don't inherit dddd (they only get dd) unless we are talking two genes one gene = 1:8 chance of recessiveness Two genes = 1:16 look at "V. Studying Two Traits at once: (Dihybrid Cross) " on this page http://www.biology.iupui.edu/biocourses/N100/2k4ch10genetics.html
in which case the nomenclature is AaBb The problem is that this can't be directly extrapolated to a population.... punnett squares only work when you consider only the parents and the offspring. On the other hand, I wouldn't go with a mendelian inheritance scheme at all. I'd probably decide to go with an Alzheimer's type pattern in which it seems that multiple copies of a specific portion of a gene (copies of a motif) lead to an increase in how early in life you get the disease. So for magery I'd say X copies = magery 1, Y copies = magery 2, and Z copies = magery 3. So most people have 2 copies and no magery. But rare people have 4 copies (2 on each chromosome) and those get magery 1, or occasionally a duplication will arise randomly and a person will have 2 copies on one chromosome and one on the other.... which =no magery. But if that person marries a mage level 1 then they have a 1:2 chance of having a mage child. If a mage level 1 marries a mage level 1 then their childern are mage level one, but there is again a chance of duplication which would result in a 1:2 chance of having a mage level 2 child.... The chance of duplication is really really low and you can always declare a higher number of copies to get magery 1 - (One form of inheritable Alzheimers that doesn't show an effect until you have 20+ repeats of a CAG motif in your genetics)... this means it's a really really low percentage of the population that gets Alzheimers from this change. That way you can have a rare trait that becomes more intense if two people with the same trait get together... and yet it still stays rare with in the population. -Sue ----- Original Message ---- From: "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> To: The GURPSnet mailing list <[email protected]> Sent: Monday, April 30, 2007 12:01:36 PM Subject: Re: [gurps] Fake scientific genetics for Magery... At 09:59 AM 4/30/2007 -0700, you wrote: >[EMAIL PROTECTED] wrote: >> Ok, after seeing some of the comments made thus far - the question I have >> is, were my numbers more or less on the money, and if so, does it make for >> a reasonable explanation? > >No, your numbers were not on the money. You're making the assumption >that there's a 50% chance of having each of the specific genes, and the >real chance can range anywhere from 0 to 100%, depending mostly on >evolutionary advantage. > >If you want to have a constant low rate of a trait, it implies that >either the trait is not significantly evolutionarily favored (seems >unlikely for magery) or that the trait is one which results in >evolutionary disadvantages if it becomes too prevalent in the breeding >pool (e.g. the gene for sickle-cell anemia gives resistance to malaria >if you have one copy, but is likely to kill you if you have two copies). > >A dominant gene that produces negative effects if it occurs twice is >pretty easy to recognize, however, and would just mean that mages always >breed with non-mages. Some combination of multiple genes is probably >more reasonable. Ok, in saying I was off the mark, you made me re-evaluate what my assumptions where rather than plot them out. A simple Dominant/Recessive trait scheme would result in the following mendel square: Mother: DD Mother: dD Mother: Dd MOther: dd Father: DD Father: Dd Father: dD Father: dd The odds of having the traits required where the child born has both dd is actually 1 in 4, rather than 1 in 2. I used the reciprocal of 2^n where n = number of gene sites required to produce a magery of a given level. The actual odds of achieving a given trait where both are recessive depends on both parents giving the child the recessive gene. When you increase the number of gene sites to 2, the odds of a child getting recessives at both sites becomes 1 in 16. Which means, that instead of the formula being the reciprocal of 2^N where N = number of genes involved, it looks like I should have used the reciprocal of 4^N where N = number of sites. Can anyone confirm? _______________________________________________ GurpsNet-L mailing list <[email protected]> http://mail.sjgames.com/mailman/listinfo/gurpsnet-l _______________________________________________ GurpsNet-L mailing list <[email protected]> http://mail.sjgames.com/mailman/listinfo/gurpsnet-l
