群体遗传与进化

1788
Genotype frequency LMLM= 397/1788 =0.222 LNLN= 530/1788 =0.296 LMLN= 861/1788 =0.482
Allele frequency LM=（397×2＋861）/ （1788×2）=0.46 LN=（530×2＋861）/ （1788×2）=0.54
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?
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）
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
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
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
Cystic fibrosis（囊性纤维化）, an autosomal recessive traits, has ቤተ መጻሕፍቲ ባይዱn incident of about 1/2500
The frequency of the recessive alleles is : q2=1/2500 → q=0.02
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
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 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
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
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
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