1 Review Define the terms genes pool and relative
frequency
Predict Suppose a dominant allele causes a plant
disease that usually kills the plant before it can
reproduce. Over time what would probably happen
to the frequency of that allele in the population
2 Explain How does genetic recombination result in
genetic variation
Relate Cause and Effect Why does sexual
reproduction provide more opportunities for genetic
variation than asexual variation
3 Explanation Explain how mutations are important in
the process of biological evolution
CH 17 EVOLUTION OF POPULATIONS
17.1 Genes and Variation

Darwin developed his theory of evolution without
knowing how heritable traits passed from one
generation to the next or where heritable variation
came from.


In genetic terms
Evolution is the change in allele frequency of a
population over time.
Genotype and Phenotype in Evolution


Natural selection acts directly on phenotype, not
genotype
Some individuals have phenotypes that are better
suited to their environment than others, produce
more offspring and pass on more copies of their
genes to the next generation.
Gene Pool

All the genes, including all the different alleles for
each gene that are present in a population.
Relative Frequency

Number of times a particular allele occurs in a gene
pool, compared with the total number of times
alleles for the same gene occurs.


Natural selection operates on individuals
Evolution operates on populations.
Sources of Genetic Variation



Mutation
Genetic recombination during sexual reproduction
Lateral gene transfer.
Mutations

Mutations that produce changes in phenotype may
or may not affect fitness
 Some
lethal or lower fitness
 Some beneficial and raise fitness

Only matter if they can be passed from generation
to generation
 Must
occur in the germ line cells that produce either
eggs or sperm.
Genetic Recombination in Sexual
Reproduction


Most heritable differences are due to genetic
recombination
We have 23 chromosomes
 Number
of combinations
 223
 8.4
million combinations of each sperm or egg.
Lateral Gene Transfer



Occurs when organisms pass genes from one
individual to another that is not its offspring
Can be same or different species
Think bacteria.
Single-Gene Traits



Trait controlled by only one gene
Just two or three distinct phenotypes
Most common form of the allele can be dominant
or recessive.
Polygenic Traits



Traits controlled by two or more genes
Each gene of a polygenic trait often has two or
more alleles
Often has many possible genotypes and even more
different phenotypes.