Experimental Inheritance and Population Inheritance

According to the Mendel's Laws, in a cross between a purebred tongue-roller and a purebred non-tongue-roller, 3/4 of the F2 descendents would be tongue-rollers and 1/4 non-tongue-rollers. But it is found that the number of tongue-rollers in a population is always far less than expected. It is because the chances of existence of the alleles are not equal. This is the difference between the experimental genetics and population genetics. The chance of existence of each allele of a gene in a population can be found throught statistics and calculation.

In a population, if the percentage of tongue-rollers is 19%, then, the percentage for non-tongue-rollers is 100% - 19% = 81%.

Owning to the fact that non-tongue-rollers are recessive homozygous, only those who has 2 recessive alleles will show this trait. If the chance of existence of this allele in the populaiton is x, then, the chance of carrying 2 of this alleles should be x² ĄC

Therefore x² = 81% = 0.81
x = 0.9
Then, the chance of existence of the tongue-roller allele is 1 - 0.9 = 0.1

In this population, the homozygous tongue-rollers should occupy 0.1 X 0.1 = 0.01 = 1%

and heterozygous :Ą@2 X (0.1) X (0.9) = 0.18 = 18%

As both homozygous and heterzygous individuals would should the trait of tongue-rolling, so, there should be a total of 1% + 18% = 19% in the population showing the trait.

Question
Thalassemia is a single-gene recessive genetic disease. People carrying one abnormal allele is called the minor thalassemia, that is not a very severe disease. Those who carry 2 of this abnormal alleles are called major thalassemia. It is very severe and requires monthly blood transfusion.

(a)	In a small town with 120000 population, if 12 are found to be major thalassemia, how many would be the minor thalassemia ?
(b)	If you want to establish you family in this small town, what is the chance to marry a minor thalassemia people ?
(c)	If you are also a minor thalassemia patient, what is the chance to guarentee all of your children would be normal (at least, apparently) ?

(25.12.2006)