• If no selection and mating is random (i.e., no processes acting to change the distribution of genotypes), then the genotypes of F
1
(daughter generation) should be the same as the genotypes of
F
0
(parent generation.

• 1 = p + q (p = dominant, q = recessive)
• 1 = p 2 + 2pq + q 2 (square both sides)
• 1 = AA + 2Aa + aa
• Genotype ratio of 1:2:1

0.5
0.5
0.5
Figure 03.02
aa = 0.5 X 0.5 = 0.25
Aa = 0.5 X 0.5 = 0.25
aA = 0.5 X 0.5 = 0.25
0.50
0.5
0.5
0.5
AA = 0.5 X 0.5 = 0.25

• In a population of 100 we have 25 blue eyed people
• Since the allele for blue eyes is recessive then the blue eyed people are “aa” (q 2 )
• 25% or .25 are “aa”
• The frequency of the allele for blue eyes = the square root of .25 = .50 (50%)
• Since p + q = 1, the allele for Brown also =
.50 (50%)

• In a population of 100 we have 16 blue eyed people
• Since the allele for blue eyes is recessive then the blue eyed people are “aa” (q 2 )
• q 2 = 16/100 or .16
• The frequency of the allele for blue eyes = the square root of .16 = .40
• Since p + q = 1, the frequency of the allele for Brown eyes is .60 (60%)

Figure 03.02

• The F
1 people population 300 of which 27 blue eyed
• Since the allele for blue eyes is recessive then the blue eyed people are “aa” (q 2)
• q 2 = 27/300 = .09
• The frequency of the allele for blue eyes = the square root of .09 = .30 (30%)
• Since p + q = 1, the allele for Brown = .70 (70%)
• The frequencies of the alleles for eye color in F are not the same as in F
0 taking place (selection or mate choice has
1 therefore evolution is changed the distributions)

• If the phenotype is result of multiple genes each having an additive effect.
• Example: tallness is controlled by 3 different genes each with 2 alleles (one for tall and one for short)
• If you get the tall allele in from all 3 genes then you get 6 tall (++++++) and you are the tallest, if you get all short you get 6 short (------) and you are the shortest.
• But if you get half of each you are in the middle
(+-+-+-), you are also in the middle if you get ++-
+--).

Tall
Short
Since all allele effects are additive (all get expressed), the you can have any combination of 3 tall and 3 short and have the same phenotype

• Multiple gene effects mean that natural selection and/or mate choice is not always favoring or selecting against the same genes
• Genes can hide in the recessive state when phenotype is dependent on multiple genes (loci).

• Soapberry bugs and mate guarding
• Frequency dependent strategy (Oklahoma population), trait is plastic
• In Florida sex ratios are stable and trait is canalized

• Pleiotrophy = genes effect more than one trait
• Correlated response = phenotype is dependent on more than one gene, therefore selection for a trait effects frequency of multiple genes at the same time
• Maladaption
• Gene drift: sampling effect, not natural selection or mate choice but random sampling variation
• Fixation