Exploring Gene Pools and Evolutionary Biology

1. 14.4 & 14.5 Gene Pools & Evolutionary Biology

2. 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

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

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

5. 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.

6. 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.

7. 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

8. 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.

9. 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.

10. 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.

11. Grant’s research on Darwin’s Finches.

12. 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.

13. Malaria trophozoites and life cycle.

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