BIOL 218 Week 04 Day 02 Notes PDF

2025-01-29 BIOL 218 Week 04 - Day 02 Last Class: Wallace and the Wallace Line Malay Archipelago Pangea and Continental Drift Misconceptions - Evolution Populations? Population-level Evolution Three drivers 1) Natural select...

2025-01-29 BIOL 218 Week 04 - Day 02 Last Class: Wallace and the Wallace Line Malay Archipelago Pangea and Continental Drift Misconceptions - Evolution Populations? Population-level Evolution Three drivers 1) Natural selection 2) Genetic drift 3) Gene flow 1 BIOL 218 TODAY AND UPCOMING (USE THIS FOR READING AHEAD): Microevolution Natural selection Genetic drift Small populations Founder effect Genetic consequences Human-induced Gene flow (Costs and Benefits) Nature vs. Nurture Phenotypic Plasticity Types of Natural Selection Directional selection Disruptive selection Stabilizing selection 2 1  2025-01-29 BIOL 218 HOUSEKEEPING READINGS: Chapter 23: The Evolution of Populations Chapter 24: The Origin of Species QUIZ 02 - OPENS TODAY @ 12PM (NOON) - COVERS WEEKS 02 AND 03 QUIZ 02 CLOSES AUTOMATICALLY @ 11:59PM ON WEDNESDAY 3 BIOL 218 Genetic Drift: The Bottleneck Northern elephant seals have reduced genetic variation probably because of a population bottleneck Hunting in the 1800s (down to 100 individuals) Cheetah genomes typically exceed 90% homozygosity 4 2  2025-01-29 BIOL 218 Microevolution - Genetic Drift What makes small populations more vulnerable to extinction? 2) Genetic drift Chance events that alter allele frequencies 5 BIOL 218 Genetic Drift: The Founder Effect Founder Effect 2) Genetic drift When a few individuals become isolated from a Chance events that larger population, this smaller group may establish alter allele frequencies a new population whose gene pool differs from the source population … Why? Example: Tiburon Island Example: When a few members of a population population of desert bighorn are blown by a storm to a new island. sheep has increased in size from 20 founders in 1975 to approximately 650 in 1999 6 3  2025-01-29 BIOL 218 Hatch success Genetic Drift - Consequences Alleles Solution (short-term)? From: Millions - 1820s To: 50 individuals left - 1993 Compared DNA of current to museum specimens 7 BIOL 218 Genetic Drift 2) Genetic drift Human-Induced - Selective harvesting Size and/or attribute-selective harvesting can Chance events that significantly affect populations in certain species alter allele frequencies (often based on size) - Examples? Example: Most fisheries only catch individuals above a minimum size that is mandated by fisheries managers or determined by the gear. The main effects of size-selective harvesting is an overall? 8 4  2025-01-29 BIOL 218 Genetic Drift: Human-Induced - Selective harvesting Example: Trophy Hunting 9 BIOL 218 Genetic Drift: Human-Induced - Selective harvesting Example: Trophy Hunting Genetic consequences of trophy-ram harvesting? 10 5  2025-01-29 BIOL 218 Genetic Drift: Human-Induced - Selective harvesting Example: Trophy Hunting - Population-level effects 11 BIOL 218 Effects of Genetic Drift: A Summary 1. GENETIC DRIFT IS MOST SIGNIFICANT IN SMALL POPULATIONS 2. GENETIC DRIFT CAN CAUSE ALLELE FREQUENCIES TO CHANGE AT RANDOM 3. GENETIC DRIFT CAN LEAD TO A LOSS OF GENETIC VARIATION WITHIN POPULATIONS 4. GENETIC DRIFT CAN CAUSE HARMFUL ALLELES TO BECOME FIXED 5. GENETIC DRIFT CAN CAUSE BENEFICIAL ALLELES TO BE LOST 12 6  2025-01-29 BIOL 218 Gene Flow Gene Flow 3) Gene flow Allele frequencies can also change with the transfer of alleles into or out of a population The transfer of alleles between populations Due to the movement of fertile individuals, or their gametes (e.g. wind pollination in plants) Beneficial: Yes. Increased genetic diversity (new alleles). Harmful??? Population A Population B 13 BIOL 218 Gene Flow 3) Gene flow Gene Flow Allele frequencies can also change with the The transfer of alleles transfer of alleles into or out of a population between populations Gene Flow … Who Cares ??? Important in Conservation Biology Roads provide a barrier to gene flow and populations become both physically and genetically isolated Wildlife Crossing Structures 14 7  2025-01-29 BIOL 218 There are three main drivers of microevolution: 1) Natural selection 2) Genetic drift 3) Gene flow Adaptations change Chance events that The transfer of alleles allele frequencies alter allele frequencies between populations 15 8