ANTH 1001 Lecture 6: Lecture 6, Bio Anth

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6 Feb 2017

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Introduction to Biological Anthropology, Week 4, Lecture 6 2/6/17
Forces of Evolution
A group of organisms potentially capable of successful reproduction
Individuals of a population tend to choose mates from within the group
Largest reproductive population is the species
Genes in Population
o The population is a unit of evolution
o GENE POOL- the sum of all alleles carried by the members of a population,
ignoring the individual people or animals it is just their genes
o EVOLUTION- a change in allele frequencies in a population from one generation
to the next
o GENETIC EQUILOBRIUM- no changes in allele frequencies- no evolution is
Hardy-Weinburg: Model of Genetic Equilibrium
o Used to determine whether or not evolutionary forces are operating on the
population, for a given genetic locus
o Measure observed genotype frequencies for a particular trait and compare them
against predicted genotype frequencies assuming no evolution is occurring
o Provides a genetic model or null hypothesis against which we can compare
observed genotype frequencies in a population to determine whether evolution is
o Two alleles
Dominant allele A = p (frequency of dominant allele)
Recessive allele a = q (frequency of recessive allele)
HWE: p + q = 1
o Chances of A combining with A, AA p x p = p2
o Chances of A combining with a or a combining with AAa p x q or q x p = 2pq
o Chances of a combining with a --- aa--- q x q = q2
o q2 is the frequency of aa
o p2+2pq+q2=1
o Step 1: calculate observed genotype frequencies
o Step 2: calculate observed allele frequencies
o Step 3: Use the HW formula to calculate expected genotype frequencies under
conditions of no evolution
o Step 4: Compare the genotype frequencies between what we actually observe
and what would be predicted if the population is at HW genetic equilibrium
Forces of Evolution
o Factors occurring in natural populations that cause changes in gene frequencies
over multiple generations
o HW equilibrium assumes that these forces are not operating
o An alteration in the genetic material
o Chance events and rare events
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