Evolution of Populations Ch. 18.1 and 18.4

Ch. 18.1: Genes and Variation

Traits Traits are heritable and vary among individuals. What processes create genetic variation in genes? How are genes related to traits?

A species is a population (large group) of organisms that are physically similar and interbreed. One species cannot interbreed with another species.

A gene pool is a common group of genes within a population. An allele is a version of a single gene (green eye allele vs. blue eye allele).

The allele frequency is the number of times the allele appears in a population. It is written as a percent. Allele frequency=(# of times a specific allele occurs)/(total number of alleles in the population)

Example: There are 20 bears in a population. 10 bears have light brown fur (BB), 5 bears have dark brown fur (Bb), and 5 bears have black fur (bb). What is the allele frequency for B? What is the allele frequency for b?

Evolution involves any change in allele frequency in a population over time. Populations, not individuals, evolve.

Natural selection acts on an individual’s phenotype, not their genotype. All populations will have individuals that are better suited to survive. Genetic variation already exists in every population.

Evolutionary fitness is an individual’s success in passing on genes to the next generation. Evolutionary adaptations are any genetically controlled trait that increases an individual’s fitness.

Simulating changes in a population You can choose: Peppered Moth Simulation OR Koi Pond Simulation, if you feel comfortable with the process of Natural Selection Both: how are allele frequencies changing throughout the population? What factors can influence fitness? What factors can influence allele frequency?

Peppered Moths

Koi Pond

Sources of genetic variation What are some ways genetic variation can occur?

Genetic variation can occur through: Mutations Genetic recombination during sexual reproduction Lateral gene transfer (This typically happens in bacteria)

Mutations Mutations are heritable changes in genetic information. Mutations in sex cells will be passed on. Mutations in somatic cells (body cells) will not be passed on.

Genetic recombination During meiosis, chromosomes get randomly sorted into each gamete AND they cross over. Both create genetic variation.

Lateral gene transfer Lateral gene transfer is the movement of genes between individuals that are not parents and offspring. This happens most commonly in bacteria.

Single Gene Traits Single-gene traits are traits that are controlled by a single gene. These are usually simple dominant or recessive. The number of phenotypes produced for a trait depends on how many genes control the trait.

Polygenic Traits Polygenic traits are traits controlled by two or more genes. These result in many different phenotypes across a whole range. Height in humans is an example.

Ch. 18.4: Molecular Evolution

New Genes New genes can evolve through duplication, followed by modification, of existing genes. Chromosomes can end up with duplicated genes during crossing-over in meiosis. Chromosomes can rearrange by breaking up and moving around or by getting new sequences from viruses, microorganisms or other genes.

Small changes to Hox genes during development can have large changes in adult organisms. One small change in a Hox gene between fruit flies and brine shrimp for leg development accounts for a major evolutionary difference.

One small change in a Hox gene between fruit flies and brine shrimp for leg development accounts for a major evolutionary difference.

Molecular Clocks We can compare the DNA sequences of organisms to determine their evolutionary relationship. A molecular clock uses mutation rates in DNA to estimate the time that two species have been evolving independently.

Neutral mutations occur at about the same rate within a species. Each mutation is like the tick of a clock. The more differences there are, the more time has passed since the two species last shared a common ancestor.