G11.4B – Evolution: Hardy Weinberg Theory Factors that influence the frequency

of genes
Learning Objectives
11.2.6.4 Factors affecting the frequency of alleles
Success

CIE Biology Jones

Bozeman Hardy Weinberg
http://www.bozemanscience.com/hardy-weinberg-equation/

gene or environment
Migration – emigration, immigration
Genetic drift Non-random mating
Selection

one time

in individuals which can be passed to their offspring. Over

Factors that influence the frequency of alleles

green colored alleles
the physical flow (movement) of alleles into or

Factors that influence the frequency of alleles

toward genes of traits that allow for more successful traits.
Factors

pool is small due to these organisms producing more offspring

Factors that influence the frequency of alleles

changing the population of alleles (genotype)
Selected against?
Factors that influence

assumptions, use the image above to guess what these could

is only true under certain conditions...
The equations are used to

If the frequency of alleles or genotypes do change then one of these must have actually occurred

remains the same in a population for many generations
if

1. No mutations can occur. 2. The population must be large. 3. All mating must be random 4. No migration can occur. 5. All genotypes must be equal

in a population over several generations

the number of copies of

one allele if you know the frequency of the other

p + q = 1

If the frequency of R is 0.4, then the frequency of w is?

0.6

one genotype if you know the frequency of the others
P2

p2 + 2pq +q2 = 1

If the homozygous red phenotype is 0.34, the heterozygous phenotype is 0.27, what is the frequency of the homozygous white flowers?

1 – 0.34 – 0.27 = 0.39

in every 2500 births. Calculate the percentage of carriers in

Remember, 2pq is the heterozygous phenotype (carrier)
This can be expressed as a percentage by multiplying by 100 = 3.9%
0.039 / 1 X 100 = 3.9 %
We can also calculate p2 (homo dominant).

3. Using both equations

p2 + 2pq +q2 = 1

p + q = 1

0.02

0.98

0.039

0.004

0.957

express the recessive phenotype, what percent of the population would

= 1
p = 1 – 0.7
p = 0.3

2pq = 2(0.3)(0.7)

a tidal wave and 100 organisms were wiped out, leaving

= 0.4

Heterozygous = 2 (0.4)(0.6) = 0.48 = 48%
Homozygous dominant

grey fur coloring in mice. If you have 168 brown

2pq
32/200 = grey fur = q2
0.16 = q2
0.4 = q
p

a given trait. Calculate
Frequency of homozygous dominant
Frequency of heterozygotes
Frequency of

= 0.18

one copy of the recessive allele
what is the predicted frequency

p2
0.7 = p
0.3 = q

p2 + 2pq =
0.49 + 0.42

is only expressed in the phenotype of homozygous recessive individuals

=
p2 + 2pq = 0.9859 + 0.1409

cystic fibrosis.
calculate the frequency of the recessive cystic fibrosis

+ 2(0.09757)(0.0243)
0.9567

with a severe form of sickle-cell anemia (ss), what percentage

0.7

2pq = 2(0.3)(0.7) = 0.42 = 42%

in a population of clams. Give the frequency of
genotypes YY,

= 0.8.
p + q = 1, then p = 1

gene or environment
Migration – emigration, immigration
Genetic drift Non-random mating
Selection

one time

in individuals which can be passed to their offspring. Over

Factors that influence the frequency of alleles

green colored alleles
the physical flow (movement) of alleles into or

Factors that influence the frequency of alleles

toward genes of traits that allow for more successful traits.
Factors

pool is small due to these organisms producing more offspring

Factors that influence the frequency of alleles