Biology 106: Lecture Topic # 8 Genetics of Populations

I. Population Genetics

A. Importance

1. need to understand how gene frequencies change in populations

2. thus need theory which can describe transmission of genes on a popln level

II. Hardy-Weinberg Theorem

A. History

1. Hardy- English Mathematician

2. Weinberg- German biologist

B. Problems

1. Blending inheritance

2. Loss of recessives

3. High mutation rates ??

C. H-W Theorem

1.Describes genetic variation in terms of allele frequencies

AA AA AA AA AA AA

Aa Aa aa aa Aa Aa

Aa AA AA Aa Aa Aa AA AA

p = # A q = # a

---------- -----------

# all alleles # all alleles

___ AA, ___Aa, ___aa = ___ copies of A; ___ copies of a

IF all gametes combine randomly:

females

A (p) a (q)

----------------------------

|

A (p) | AA p2 Aa pq

males |

a (q) | Aa pq aa q2

Genotype Frequency in population

AA p2

Aa pq + pq = 2pq

aa q2

H-W law of genetic equilibrium: p2 + 2pq + q2 = 1

GIVEN HWE:

D. Conclusions

1. allele freq. remain constant from generation to generation

2. genotype freq. remain constant after1 generation of random mating

3. mendelian laws of inheritance DO NOT cause allele frequencies to change

E. Applications

1. predict genotype freq. from allele freq.

2. predict allele freq. from genotype freq.

eg. W dominant to w; purple flowers Ww or WW = white flowers ww =

III. Take Home Message of Hardy-Weinberg Equilibrium

A. allele and genotype freq. remain constant from generation to generation if:

B. No mutation

C. Population large

D. No migration

E. No selection

F. Random Mating