Housekeeping
• TT1 Preparation Assignment
– Due 9 AM Feb 11
– 10 questions, based on lectures 1-9
• Term Test 1
– Feb 16 1:10-3:00 PM
– Lectures 1-9
– MC questions + SA questions + calculation
questions
– Equation sheet posted on Quercus (> Home)
Educational Goals
• Understand how negative and
positive assortative mating affect
heterozygosity
• Outline the effects of inbreeding on
fitness
• Understand the principles and
predictions of genetic drift and how it
affects evolution
• Describe the neutral theory of evolution
Dispersal as a mechanism of evolution
(in the absence of other factors)
Conclusion 1: In the absence of
gene flow, two populations will
remain genetically diverged.
m =
0
Gene flow/Dispersal (On its Own)
• 2 scenarios for dispersal only mechanism
◦ Without gene flow
‣ m = 0 ---> 2 popula<ons remain gene<cally diverged
• Maintain varia<ons in their own popula<ons in absence of evolu<on, but
not share genes so remain diverged!
◦ Presence of gene flow
‣ m>0 ---> gene<c divergence between popula<ons decreases
• Thus, gene flow acts to homogenize popula<ons
◦ Draws popula<ons gene<cally together
2 types of non random ma<ng
• Posi<ve assorta<ve ma<ng (PAM)
• Nega<ve assorta<ve ma<ng (NAM)
• Inbreeding depression
• We talked about the mechanisms of muta<on, selec<on, dispersal/gene flow
• So today we're talking about the mechanisms of Nonrandom Ma;ng & Gene;c dri=
Dispersal as a mechanism of evolution
(in the absence of other factors)
Conclusion 2: In the present of
gene flow, genetic divergence
between populations will decrease.
In other words, gene flow
homogenizes populations
m > 0
Gene flow + selection
Proportion of dispersers in
population
Fitness of
population
IN SMALL
POPULATIO
NS
Gene Flow and Selec<on (Together)
• There are different cases when gene flow acts alongside selec;on
Intermediate Gene flow = Op<mal Fitness
• An intermediate amount of dispersal/gene flow (when working alongside selec;on*) lends itself to op;mal
fitness of popula;on b/c selec;on feeds on intermediate amount of gene flow
3 scenarios of gene flow + selec;on for fitness (See graphs above)
1.Low dispersal
• Rescues small inbred popula<ons
• A liUle gene flow doesn't give selec<on a lot of varia<on to play with; it's mostly varia<on already exis<ng in island
popula<on

small inbred popula<ons***
2.Intermediate dispersal