Chapter 17: Evolution of Populations

Transcription

1 Chapter 17: Evolution of Populations Population Genetics Population genetics Study of Mendelian Genetics as applied to Darwinian Evolution A. Gene Pool the total number of genes in a population at any one time Species Similarly related organisms that can exchange genetic information (Interbreed) and produce fertile offspring Population a group of organisms of the same species in a population that are geographical isolated and randomly interbreed B. Allele Frequency The rate of occurrence of an allele in a population Percentage of total alleles for a trait in a population We assume the variations that are the most fit are the only ones that are passed down but sometimes our judgment is contrary to evolutionary theory This causes SPECIATION! The formation of new species via the passing down of more successful (more fit) alleles! 1

2 Speciation The Formation of New Species Through Reproduction and Small Genetic Changes Over Time. Genetic drift, Natural selection, Mutation, and Isolation are the key factors in the formation of new species 2

3 A. Genetic Drift: Random genetic changes to a population usually caused randomly or by random events 1. Bottleneck: Caused by some catastrophic event that eliminates many of the genes in the gene pool at once (ie. Volcanic eruption). Only some alleles survive to from a new species 2. Founder Effect: Occurs when members of a parent population migrate to a new area and leave alleles behind. Shrinks the Gene Pool: Limits Genetic Variation Genetic Variety in the Ramapough Mountain Indians They are clearly racially mixed. There are elements from native Indian, Negro, Dutch, and possibly German (Hessian) and Italian blood lines. Their isolation has resulted in a high degree of intermarriage among the families which has, on occasion, produced genetic anomalies such as syndactyly (fusion of fingers or toes), polydactyly (extra fingers or toes), pie baldness, albinism, sometimes distinguised by a grayish skin color, and mental retardation. Ramapough Mountain People The Jackson Whites A Pathfinder and Annotated Bibliography by: Randy D. Ralph, MLIS, Ph.D. ARSACS in Quebec Polydactyly in the Amish 3

4 B. Natural Selection 4 types of selection a. Directional selection b. Disruptive selection: c. Stabilizing selection d. Artificial selection Can be either of our first two types of selection but the environmental influence is driven by man Peppered Moth and Industrial Revolution: Pre Industrial Revolution Post IR 4

5 C. Isolation: Either Reproductive (Eww..your gross, I would never reproduce with you) Geographic (Hey..your cute..i would totally reproduce with you if this river weren't in the way) Can include variations in temp, water availability, altitude Behavioral (Hey..your cute..but I am more of a morning person..and your a slob so this will never work out) Temporal (We are just at different points of our life...it will never work out) 5

6 D. Mutations In stable environments, mutations often result in little or no benefit to an organism, or are often harmful Mutations are more beneficial (rare) in changing environments (Example: HIV resistance to antiviral drugs). E. Genetic Recombination source of most genetic differences between individuals in a population F. Co evolution Often occurs between parasite & host and flowers & their pollinators 6

7 Speciation in Darwin's Finches: 7