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Western University
Anthropology 1020E
Alexis Dolphin

Januray 17/2013 Lecture 4 Inheritance and Macroevolution Chapter 3 and 5  Mendelian genetics  Forces of evolution  Speciation Mendelian Genetics:  1822-1884  How physical traits could be expressed in plant hybrids 1. Simple monogenetic traits (one gene) 2. Experiments with pea plants published 1866 3. Crossing tall pea plants and short pea plants  Found blending theory (thought that medium size) not true  he found that when crossing some short and some tall 4. He was able to systemically approach the problem like Darwin  Came up with two principles 1. Principle of segregation:  Genes code for particular traits  Genes come in different version (alleles) that have different effects ( there can be different outcomes)  Each parent has 2 alleles for a trait (one on each chromosome, at the same locus)  Offspring gets only 1 allele from each parent  With fertilization  Dominant and recessive  Homozygous-both alleles the same (tall,tall)  Heterozygous-both alleles different (tall, short)  Dominant-masks effect of other alleles (T)  Recessive-effect masked by other allele (t)  Codominant-both alleles expressed 2. Principle of independent assortment  Distribution of pair of alleles into gametes does not influence the distribution of another pair  Genes controlling different traits are inherited independently of another From Gene to Trait  Genotype- combinations of 2 alleles that code for a trait, genetic makeup o TT or Tt  Phenotype- the chemical/physical results f the combination of alleles (ex. Tall pea plant) Mendelian Inheritance in Humans o Mendelian traits  Influenced by alleles at only one genetic locus  Discrete (discontinuous) phenotypes  More than 4/500 human traits table 3-2 o Cheek dimples (dom) o Albinism (rec) o Freckles (dom) o Hitchhikers thumb (rec) ABO GENETYPES AND PHENOTYPES o 3 alleles: A,B,O o Antigen: molecules found on the surface of cells Polygenic Inheritance o Alleles at two or more loci with each making a contribution to the phenotype o All contribute to phenotype o Continuous variation o Most of observable variations o Skin colour o Hair colour o Eye colour Evolution  Define: A change in allele frequency from one generation to the next  Allele frequencies are the proportions of alleles in a population  Evolution is a change in these proportions  Population: a community of individuals where mates are usually found A two stage process: 1. Production and redistribution of variation 2. Natural selection (whereby genetic differences in some individuals lead to higher reproductive success) Factors that Initiate Changes in Allele Frequencies Include those that: 1. Produce new variations (mutations) 2. Redistribute variation through genetic drift 3. Redistribute variation through genetic drift 4. Selection of advantageous allele combinations that promote reproductive success (natural selection) 1.Mutation o Random change in the genetic code (base, chromosome) o Ultimate source of new genetic variation o Beneficial, deleterious, or neutral o Point mutation o Hghb a: GGT-CTC-CTT o Hgb S:GGT-CAC-CTT o Substitution of one base o Sickle shaped red blood cells  Sickle cell anemia 2.Gene Flow o Frequency of the populations change when the populations come together and mix o Frequencies shift when populations get together and mix alleles o Exchange genes between two populations 3.Genetic Drift o Random fluctuations in allele frequencies o Based on notion of sampling
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