Ch. 20 – Mechanisms of Evolution 20.1 – Population Genetics macro-evolution – evolution on a large scale, such as the evolution of new species from a common ancestor

micro-evolution – evolution on a small scale, change in the gene frequencies within a population over time.

Darwin’s original theory of natural selection could not account for the mechanism of traits. He could not explain where the variation which existed among organisms comes from. It was not until Gregor Mendel released his work on heredity in pea plants that scientists began to link ideas about genetics and evolution. In the 1930s, the study of population genetics showed that mutations could occur within the genes of a population and these mutations provided genetic variation within a population. Modern synthesis – the modern contributions of Mendel’s and Darwin’s theories of evolution

Review of the Language of Genetics Alleles – alternative form of a gene. Ex. In humans, there are 3 alleles which help determine blood type Locus – the location of a gene on a chromosome Dominant allele – in a heterozygous pairing, the allele that is fully expressed in an organism’s phenotype Recessive allele – allele that is not expressed in an organism’s phenotype in a heterozygous pairing

Review of the Language of Genetics Homozygous – describes an individual with two alleles at one locus which are identical Heterozygous – describes an individual with two different alleles at a locus Genotype – genetic makeup of an organism; remains constant throughout an individual’s life Phenotype – the physical and physiological traits of an organism

Review of the Language of Genetics Incomplete dominance – blending of traits of two different alleles at one locus that occurs when neither alleles is dominant Co-dominant – in genetics, describes a situation in which two alleles may be expressed equally. This situation occurs when two different alleles for a trait are both dominant

Population Genetics Population – group of individuals of the same species living in the same geographical area All of the genes in a population or, more specifically, all of the alleles at all gene loci in all individuals of the population, make up the population’s gene pool. Polymorphic – describing genetic loci that have more than one allele

Population Genetics Fixed – in genetics, describing a population in which all members are homozygous for the same allele Population genetics studies the frequencies of alleles and genotypes in populations. The study of population genetics is important to the study of micro-evolution because changes in the genetic variability within the population can be used to determine if a population is undergoing micro-evolution. (see fig 20.7, p. 679).

Population Genetics frequency – in genetics, the number of occurrences of a particular allele in a population divided by the total number of alleles in a population Genetic structure – the frequencies of all alleles and genotypes in a population.