Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Sexual selection wikipedia , lookup
Evolving digital ecological networks wikipedia , lookup
Evidence of common descent wikipedia , lookup
Punctuated equilibrium wikipedia , lookup
Inclusive fitness wikipedia , lookup
Theistic evolution wikipedia , lookup
Hologenome theory of evolution wikipedia , lookup
Natural selection wikipedia , lookup
Saltation (biology) wikipedia , lookup
Ch. 15.3 Shaping Evolutionary Theory Mr. Gaede | Biology I. POPULATION GENETICS Q: 1900s – Why don’t dominant alleles take over recessive alleles in a population? A: 1908, scientists Hardy & Weinberg– Discovered evolution will not occur in a population unless allele frequencies are acted upon by forces that cause change Hardy-Weinberg Principle: When allele frequency 𝑣 stays constant pop. is in genetic equilibrium (EQ) NOT EVOLVING I. POPULATION GENETICS Conditions of Hardy-Weinberg EQ: For allele 𝑣 to stay the same: 1. No mutations 2. No migration (gene flow) 3. Large population size 4. No natural selection 5. Random mating Evolution is always occurring because these conditions can never be met II. GENETIC DRIFT Genetic drift— change in the allele 𝑣 in a population due to chance (crossing over of DNA during Meiosis) Occurs in small populations Recessive individual breeds more than normal & allele 𝑣 increases quickly Reduces genetic variation II. GENETIC DRIFT 1. Founder Effect Occurs when a small sample of a population settles in a location separate from the rest of the pop. 2. Bottleneck Effect Occurs when a population declines to very low number + then recovers problem: loss of genetic variability Northern Elephant Seals • Bottleneck Event: Human Hunting (1890s) • Population decreased to 20 seals • NOW ~30,000 seals w/ reduced variation III. GENE FLOW Gene flow – (AKA: migration) organisms move from one population to another Increases genetic variation IV. NONRANDOM MATING Nonrandom mating – Organisms choose their mates based on proximity Genetic variation decreases V. NATURAL SELECTION Natural Selection – Organisms with traits well suited to their environment survive and reproduce at a greater rate than un-fit organisms in the same environment V. NATURAL SELECTION Stabilizing selection Eliminates extremes of trait when middle phenotype is better for the environment V. NATURAL SELECTION Directional selection Selects for one extreme Population average moves in one direction V. NATURAL SELECTION Disruptive selection splits a population into two groups often the cause of speciation selects against the middle Individuals w/ extreme variation of a trait have greater fitness than individuals w/ the average form of the trait VI. SEXUAL SELECTION Organisms choose a mate based on a behavior or appearance Male competition & female choice Ex: peacocks and peahens VII. REPRODUCTIVE ISOLATION Prezygotic (before zygote) Fertilization is unlikely Different mating behaviors Ex: E. vs W. meadowlark song Postzygotic (after zygote) Can physically reproduce but offspring are sterile Ex: Liger or Mule E. Meadowlark & W. Meadowlark Liger VII. REPRODUCTIVE ISOLATION Geographic Isolation (allopatric speciation) Population separated from another population by the land barrier (geography) Genetic differences over time prevent mating Antelope Squirrels vs. Grand Canyon VIII.PATTERNS OF EVOLUTION Adaptive Radiation (divergent evolution) Evolution of an organism into a wide variety of different types, each fill different ecological niches Niche – role of an organism in its environment Occurs after large extinctions Cichlid Fish 300+ different species VIII.PATTERNS OF EVOLUTION Coevolution The relationship between 2 species is so close that the evolution of one species affects the evolution of the other Mutualism – benefits both Hummingbirds & Flowers Beaks have evolved to fit shape VIII.PATTERNS OF EVOLUTION Convergent Evolution Unrelated species evolve similar traits even though they live in different parts of the world Occurs in environments w/ similar ecology VIII.PATTERNS OF EVOLUTION Rate of Speciation Theories 1. Gradualism Evolution occurs in small gradual steps over time 2. Punctuated Equilibrium Rapid spurts of genetic change cause species to diverge quickly Q: What are the healthiest populations? Large populations with lots of genetic diversity! They are least likely to change. Large populations with the most diversity are most likely to survive a disease outbreak. Small populations where many mutations occur are most likely to evolve. https://www.youtube.com/watch?v=cW45C9BY1aU (Bird Beak Lab Video)