Download Alleles in a Population

Genes and Variation
EQ: How is the gene pool affected by selection pressure?
Genotype and Phenotype
Genotype: particular combination of alleles
Phenotype: physical, physiological, and behavioral characteristics
Allele Frequency
Number of times an allele occurs in a gene pool, as a percentage
of the total occurrence of all alleles
In 50 alleles:
In 100 alleles:
40
20 alleles are B (black)
30 alleles are b (brown)
are B (black)
60
are b (brown)
Alleles in a Population
Evolution involves any change in the frequency of alleles in a
population over time.
Mice population = 25 mice
12
4
9
Single-Gene Traits
Phenotypic ratios are determined by the frequency of alleles and
by whether the alleles are dominant or recessive.
77%
23%
Overview: Genes and Variation
Evolution occurs due to the change of the relative frequency
of alleles in a population over time.
The alleles in an organism do not change during the
organism’s lifetime.
Evolution Versus Genetic Equilibrium
If a population is not evolving, the
population is in genetic equilibrium.
(Allele frequencies are not changing)
Hardy–Weinberg principle
Population should remain constant if
all 5 conditions are met:
1.Large population
2.Random mating
3.No natural selection
4.No immigration/emigration
5.No mutations
Hardy–Weinberg Principle
and
In words, this is stated:
(frequency of AA) + (frequency of Aa) + (frequency of aa) = 100%
and
(frequency of A) + (frequency of a) = 100%
If p = 0.40 and q = 0.60:
Probability of genotype Aa:
aa:
AA:
16%
48%
36%
Hardy–Weinberg Principle
And
Try this: Population of quackers
Dominant: B = dark feathers
Recessive: b = light feathers
In a population of 50 ducks, 10 were light and 40 were dark.
(Frequency of homozygous recessive organisms - bb)= q2 = ____
(Frequency of recessive allele - b) q = _______
(Frequency of dominant allele - B) p = _______
(Frequency of homozygous dominant organisms - BB) p2 = ______
(Frequency of heterozygous organisms - Bb) 2pq =________