14.4 & 14.5 Gene Pools & Evolutionary Biology

Gene Pool Definition- all the alleles of a population. A population -smallest level of evolution. Reservoir of genes for natural selection. Supplies genetic variation. –Mutations –Sexual recombination- meiosis and fertilization

Frequency of alleles – How often certain alleles occur in the gene pool. Usually expressed as decimal or a percentage,

Microevolution Generation to generation change in the allele frequency. 2 main factors that can change allele frequency are- –Genetic drift –Natural selection

Genetic Drift Definition-a change in the gene pool due to chance. –The smaller the population the greater the impact of genetic drift. – Larger populations are more stable and not affected.

Reduction in population size- –reduces the gene pool –reduces genetic variation in a population. 2 situations that have big effects on a population. 1. Bottleneck Effect- disasters – –Earthquakes, floods, fires, droughts –Drastically reduce pop. size; –new population has less variation. –May affect a population’s ability to adapt. –Ex.- cheetah pop. 2. Founder Effect- a few individuals colonize a new habitat. –Galapagos Island species.

Lesser factors for changing allele frequencies 1. Gene Flow – –The exchange of genes with another population. –Migration of fertile individuals between populations. –Gene flow reduces genetic differences between populations

2. Mutations – change in DNA –If carried by a gamete- enters the gene pool. –Original source of variation. –Important in asexually reproducing organisms- bacteria. If favorable ; rapid increase in gene pool due to natural selection. If unfavorable; decrease in frequency.

Natural Selection Not random Leads to adaptation Biological Fitness- Contribution to the gene pool of the next generation of the most “fit”. Production of healthy, fertile offspring is what counts.

Darwin’s Finches Peter and Rosemary Grant’s Research 30 yr. Study in the Galapagos. 2 species of finches with different beak sizes. Their data related beak size to changes in environment- wet and dry seasons and types of seeds available. Data provided evidence for natural selection occurring in a shorter time span.

Grant’s research on Darwin’s Finches.

Evolutionary Biology 14.5 Natural Selection and Sickle Cell Disease. –Sickle Cell Disease- abnormal shaped rbcs- 2 alleles needed for the disease –Heterozygous- no disease but immunity to malaria. –30% of the African population is heterozygous in endemic malaria areas. –Natural selection maintains a higher allele frequency.

Malaria trophozoites and life cycle.

Antibiotic Resistance- evolution in action Natural selection –Resistant strains of bacteria –Huge public health issue »Resistant tuberculosis »Methicillin resistant staphylococci.