LEQ: How has knowledge of genetics influenced modern

ideas about evolution?13.6 to 13.8

Populations are units of evolution

Population Species

A group of interacting individuals belonging to one species and living in the same geographic area

A group whose members possess similar anatomical characteristics and have the ability to interbreed

Populations are units of evolution

Population Genetics Modern Synthesis

The study of genetic changes in populations; the science of microevolutionary changes in a population

A comprehensive theory of evolution that incorporates genetics and includes most of Darwin’s original ideas, focusing on populations as the fundamental units of evolution (individuals don’t evolve – populations do)

Populations are the units of evolution

Gene Pool Example

All of the alleles for all of the loci in all individuals in a population

Each allele has a frequency in the population

Example: you have a wild boar population in which 50 percent of the alleles for a particular gene are dominant (B) and 50 percent of the alleles for the gene are recessive (b).

Populations are units of evolution

Microevolution example

A change in a populations gene pool over a succession of generations; evolutionary changes in species over relatively brief periods of geologic time

Change in the allele frequency over time

The gene pool of nonevolving populations remains constant…

Hardy Weinberg Equilibrium

5 Conditions of Hardy Weinberg

Named for 2 men who figured out that the shuffling of genes that occurs during sexual reproduction, by itself, cannot change the overall genetic make-up of a population

p + q = 1 (p = dominant allele frequency / q = recessive allele frequency)

p2 + 2pq + q2 = 1 ( p2 = homo dominant; 2pq = hetero; q2 = homo recessive)

1. Large population2. No migration in or out3. Mutations do not alter

gene pool4. Random mating5. Natural selections

does not occur (all have equal chance to survive)

Hardy Weinberg equation is useful in public health science

PKU – autosomal recessive trait

About 1 in 10,000 babies born in the US have PKU

How many people are carriers?

First step: calculate q2 (individuals with PKU / homo recessive)◦ q2 = 1/10,000 = 0.0001

Solve for q (the frequency of the recessive allele in the population)◦ q = q2 = 0.01

Use the equation “p + q = 1” to solve for p.◦ p = 0.99

Use the equation “p2 + 2pq + q2 = 1” and solve for carrier genotype.◦ 2pq = 2(.99)(.01)

= .0198◦ ~2% of the population

are carriers

Example #2

Try it yourself Answer

You have sampled a population in which you know that the percentage of the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate the following:◦ The frequency of the "aa"

genotype.◦ The frequency of the "a" allele.◦ The frequency of the "A" allele.◦ The frequencies of the

genotypes "AA" and "Aa."◦ The frequencies of the two

possible phenotypes if "A" is completely dominant over "a."

q2 = .36 q = .6; frequency of “a”

allele is 60% p = .4; frequency of “A”

allele is 40% p2= .16; frequency of AA

is 16% 2pq = .48; frequency of

Aa is 48% Frequency of A

phenotype is 64% Frequency of a

phenotype is 36%