Week 7.2 Ch 4 Microevolutionary Proceses 1
Mendelian Traits vs Polygenic Traits Mendelian -discrete -single gene determines effect -rarely influenced by environment Polygenic: -continuous -multiple genes determines effect -often influenced by environment Both -determined by Mendelian principles at specific loci -Dominance and recessiveness still a factor 2
Modern Evolutionary Theory Modern synthesis in the later 1920s-early 30s. Evolution described in two stages Stage 1: Different processes generate and distribute variation in a population Stage 2: Natural selection acts on variation leading 3
Stage 1: processes create and distribute variation in a population 1. Mutation: any changes in DNA E.g., point mutation - substitute of a single DNA base ONLY way NEW genetic information is created -slow rate, only combined with natural selection do rapid evolutionary changes occur 4
Stage 1: processes create and distribute variation in a population 2. Gene flow: exchange of genes between populations I.e., migration: members of one gene pool move into another gene pool and interbreed 5
Stage 1: processes create and distribute variation in a population 6
Stage 1: processes create and distribute variation in a population 3. Genetic drift: changes in allele frequencies due to chance -larger effect on smaller populations Founder effect: smaller subpopulation leaves larger population -the new population will resemble the founders instead of original population Genetic Bottlenecking: a population shrinks and then recovers -often due to catastrophic events -the new population will reflect genetic diversity of survivors 7
Stage 1: processes create and distribute variation in a population 4. Recombination: paired chromosomes exchange DNA during meiosis -genes sometimes adjust to different environments Associated with which principle of inheritance? 8
Stage 2: Natural selection acts on variation Mutation, gene flow, genetic drift, and recombination produce/distribute variation NS produces directional variation depending on the environmental context Environmental changes influence selection pressures which influence changes in allele frequencies which are described as. Adaptations: shifts in allele frequencies in response to the environment 9
Macroevolution -larger scale change over geologic time Classification: scientists attempt to make sense of the vast biological diversity involved in macroevolution -classify organisms to understand evolutionary relationships Kingdom: Animalia Phyla: 20 major phyla including Phylum Chordata Class: Mammalia is a class of chordates Order: Primate Family: Hominidae Genus: Homo Species: sapiens 10
Macroevolution Classification attempts to track evolutionary relationships - common ancestry Homologies: structures shared by species because of descent from a common ancestor Not to be confused with analogies: similar structures seen on species due to functional demands https://evolution.berkeley.edu/evolibrary/article/0_0_0/similarity_hs_02 11
Macroevolution Classification attempts to track evolutionary relationships - common ancestry Homologies: structures shared by species because of descent from a common ancestor Not to be confused with analogies: similar structures seen on species due to functional demands 12