Lecture 12 Flashcards
What causes adaptation?
Natural Selection
Briefly explain natural selection?
Selecting advantageous allele thereby increasing the allele frequency in a population
Natural Selection occurs when:
fitness is unequal
Fitness:
measure of how well individuals of a certain genotype are expected to survive and reproduce
Absolute Fitness
mean number of offspring an individual of a particular genotype has
Relative fitness
degree to which individuals of a particular genotype reproduce relative to other genotypes (the highest will be set to 1, ie 12/12 and the others are divided by the denominator of the highest)
Big W and little w mean:
W = absolute w=relative
W(AA) vs w(AA) (imagine this as subscript instead of parentheses)
W(AA) is absolute fitness of AA w(AA) is relative fitness of AA
If Absolute fitness of AA=6 Aa=3 and aa=1 what are the relative fitness values?
AA= 6/6 Aa= 3/6 aa=1/6
How do you determine w bar (mean fitness)
take the Hardy-Weinberg equation and multiply each term (the frequency of each genotype) by the fitness of that genotype. Add those up and you get the mean fitness - wbar = p^2w(AA) + 2pqw(Aa) + q^2w(aa)
How do you determine the adult genotype frequency using Wbar and relative frequencies
p^2(wAA)/wbar =Freq(AA) for adult (use the same process for 2pqw(Aa) and q^2w(aa) - the three added should equal one if done correctly
Using the adult genotype frequencies from the wbar/fitness equations, how do you find allele frequencies?
Freq(AA) + 1/2[Freq(Aa)] = Freq(A)
1 - Freq(A) = Freq(a)
Reproductive Isolation occurs when:
ancestral population splits - then those populations experience divergence - if reunited, hybridization is prevented.
Prezygotic barriers:
habitat isolation
behavioral isolation
temporal isolation
morphological isolation
postzygotic barriers
hybrid inviability (weakness)
hybrid sterility
Examples of habitat isolation
aquatic vs terrestrial, mountain vs valley
Temporal isolation example
one may reproduce in spring, the other in summer
behavioral isolation example
mating dances in birds, flashing signals in lightning bugs
mechanical isolation example
the parts do not go together to create offspring (pelvis or genital shape)
What happens with incomplete isolation?
Hybrids
How do hybrids result in postzygotic isolation
sterile offspring (liger, mule) - some hybrids do not survive
Dobzhansky Muller model of postzygotic isolation
Mutations during divergence results in alleles that have never ‘seen’ each other and result in an unfit zygote
Reinforcement
the evolution of prezygotic barriers in selective response to postzygotic isolation
what are some consequences of fertile hybrids?
Extinction or fusion, introgression, reinforcement, hybrid speciation
