Aim: How does classical genetics affect the theory of evolution?

Did Darwin know anything of Mendel’s work of Classical

Genetics?

NO!!!! Darwin understood the connection between natural selection and adaptation to the environment.However, he could not explain how the variations thatare the basis for natural selection pass from onegeneration to the next.

Darwin Mendel

What was the result?

Natural Selection + Genetics PopulationGenetics

Remember, individuals do not evolve, populations do.

Population- a group of individuals of a single speciesthat live in a specific area.

What is Population Genetics?The study of changes in the genetic makeup ofpopulations.

An important concept in population genetics is theGene Pool:

All the alleles (alternative forms of genes) in all theindividuals that make up a population.

What is the significance of a population’s gene pool in

evolution?The gene pool is the “reservoir” from which the next generationdraws its genes.

The population’s gene pool is also where genetic variation (the rawmaterial of evolution) is stored.

The variation in phenotype (appearance) of this population of flowers is determined by the combination of alleles in the gene pool.

The phenotype of the offspring are also determinedby the alleles in the gene pool.

What is Allele Frequency?How often certain alleles occur in the gene pool (usuallyexpressed as a percentage).

R = 14/20 (70%)

r = 6/20 (30%)

The Hardy-Weinberg Law:The condition in which allele frequencies do not changefrom one generation to the next.

The population is said to be in genetic equilibrium.

Ex: A population of two individuals has the followinggenotype: Rr and Rr.

1)What is the allele frequency of R?2)What is the allele frequency of r?3)What are the predicted genotypes of their offspring?4)What are the allele frequencies of the population ofthe offspring?

**Sexual Reproduction alone does not affectGenetic Equilibrium

Hardy-Weinberg Equation:

p2 + 2pq + q2 = 1 and p + q = 1

p = frequency of the dominant allele in the populationq = frequency of the recessive allele in the population

p2 = percentage of homozygous dominant individualsq2 = percentage of homozygous recessive individuals

2pq = percentage of heterozygous individuals

What happens when changes do occur to the gene pool (frequencies

of alleles change) from one generation to the next?

EVOLUTION

What leads to changes in the gene pool?

1)Genetic Drift- a change in a gene pool due to chance. **Causes changes in gene pools in small populations.

2)Mutation- changes in DNA lead to changes in allelefrequency.

3) Gene Flow (Migration)- as individuals move into a population, they bring in genes not already present. As individuals move out of a population, they take genes out of a population.

What leads to changes in the gene pool?

4)Natural Selection- the reproductive success of some organisms within a population can also changeallele frequencies (gene pool).

What conditions must be met for the Hardy-Weinberg Law to hold

true?The gene pool remains the same from generation togeneration.

1) The population must be large. In a small population, alleles of low frequency may be lost due to genetic drift.2)Individuals must not migrate into or out of apopulation.3)Mutations must not occur.4)Reproduction must be completely random. This means that every individual, whatever its genetic,makeup, should have an equal chance of producingoffspring (no natural selection).

Why is the Hardy-Weinberg Law useful when it can’t apply to real

world situations?It is important because it allows us to discover

whether or not evolution is occurring in a population.

Change in allele frequencies(gene pool)

= Evolution

Microevolution- is evolution on the smallest scale – a generation-to-generation change in the frequenciesof alleles within a population.

Macroevolution- major biological changes that areclearly visible.