Allele frequency is the proportion of all alleles that are of specified allele type.
MN blood type in human
M blood type（LMLM）：397 N blood type （LNLN）：530 MN blood type （LMLN）：861
Calculate the expected number of genotype T T = 0.3696×1050 = 416.75 t t = 0.1369×1050 = 143.74 T t = 0.4662×1050 = 489.51
4. The Hardy-Weinberg law provides a method for calculating the frequency of heterozygotes in a population
Cystic fibrosis（囊性纤维化）, an autosomal recessive traits, has an incident of about 1/2500
The frequency of the recessive alleles is : q2=1/2500 → q=0.02
of survival and equal reproductive success. That is, there is no selection.
Then, the population has the following properties
The allele frequencies in the population do not change from generation to generation
群体遗传学研究基因在群体中的遗传行为
第一节 Hardy-Weinberg 定律
1. Genotype frequency and allele frequency 基因型频率与基因频率
Genotype frequency is the proportion of organisms that have the particular genotype.
Allele frequency T: p=(410×2＋500)／(1050×2)=0.63 t: q=(140×2＋500)／(1050×2)=0.37
Calculate the expected frequency of genotype
T T= p2 =0.632 = 0.3969 t t = q2 =0.372 = 0.1369 T t = 2pq =2×0.63×0.37 = 0.4662
第十二章 群体遗传与进化
Population Genetics and Evolution
How do new diseases emerge in human populations?
Why do diseases persist in all living organisms?
What cause diseases and pests long under control to resurge in frequency and intensity?
2. Hardy-Weinberg Law
If a population conforms to these assumptions The population is infinitely large The individuals mate at random No new mutations appear in the gene pool No migration into or out of the population Individuals of all genotypes have equal rates
3. Testing for Equilibrium
Taste for PTC (苯硫脲） T T, T t, t t
T T: 410 T t: 500 total:1050
t t: 140
Genotype frequency TT= 410/1050 = 0.39 Tt= 500/1050 = 0.48 tt= 140/1050 = 0.13
1788
Genotype frequency LMLM= 397/1788 =0.222 LNLN= 530/1788 =0.296 LMLN= 861/1788 =2
Allele frequency LM=（397×2＋861）/ （1788×2）=0.46 LN=（530×2＋861）/ （1788×2）=0.54
After one generation of random mating, the genotype frequencies reach equilibrium, and can be predicted from the allele frequencies.
p2 + 2pq + q2 = 1 p + q =1
The goal of population genetics is to understand the genetic composition of a population and the forces that determine and change that composition.
Key concepts
Population: is a group of interbreeding individuals of the same species that inhabit the same space at the same time.
The sum total of all alleles carried in all members of a population is a population’s gene pool （基因库）