vikorr wrote:The quote attributed to me in your post, is a quote from a webpage. You apparently didn't read the full quote either -
I am well aware of where the quote came from. I just didn't take the time to worry with the mechanics of posting.
I also see sterilization and extermination as two separate German crimes. Sterilization was Nazi policy long before extermination was.
Quote:The part on how defective genes are passed on is a little irrelevant if the percentage of people carrying defective genes is growing...
You have documentation that the number of people carrying such genes is growing? No. Whether or not gene frequency is changing in a population depends on how genes behave, so my explanation is very relevant. Without mutations and without controlling mating habits in a population, it is biologically impossible for gene frequencies to change.
Quote:my question at the start was related to this - what happens 5, 6...10...20 generations down the track - will everyone have an illness/allergies, or multiple illnesses/allergies?
No. A homozygous dominant parent can only pass dominant genes to the next generation with 100% certainty. A homozygous recessive parent could die before reaching puberty depending on the gene's effects, but if such a parent does produce offspring he/she can only pass the a gene to the next generation with 100% certainty.
Furthermore, a heterozygous parent has an equal chance of passing either the dominant or the recessive gene on to the next generation every time he/she produces offspring since genes are transferred to gametes at random as long as they are not found on the exact chromosome. There is a 50% chance that a heterozygous parent will pass the A gene and a 50% change that he/she will pass the a gene.
In any infinitely large population where mating pairs are formed at random and genes do not mutate, gene frequencies remain the same from one generation to the next due to the Hardy-Weinberg law.
http://en.wikipedia.org/wiki/Hardy_weinberg
A gene is either dominant A or recessive a.
The possible parents are AA, Aa and aa.
Mating AA and AA has only 1 possible offspring AA. This mating has a 100% chance of producing AA:
A A
A AA AA
A AA AA
Mating aa and aa (assuming that someone with the aa genotype can mate) has only 1 outcome aa. This mating has a 100% chance of producing aa:
a a
a aa aa
a aa aa
Mating Aa and aa has 1 possible offspring Aa. This mating has a 100% chance of producing Aa:
a a
A Aa Aa
A Aa Aa
Mating Aa with Aa has 3 possible offspring AA, Aa and aa. This mating has a 50% chance of producing Aa, a 25% chance of producing AA and a 25% chance of producing aa:
A a
A AA Aa
a aA aa
In this population:
The frequency of the A gene is p
The frequency of the a gene is q
The frequency of AA is p^2;
The frequency of Aa is 2pq;
The frequency of aa is q^2.
P^2 + 2pq + q^2 = 1.
Thus the a gene never goes extinct in this population and the possibility of producing someone with the aa genotype is always present.