Chapter 9 Flashcards
Most of Darwin’s theory involved what kind of variation?
Continuous variation (gradual change)
Compensatory mutations
These mutations do not reduce the degree of resistance, but reduce/ eliminate the fitness cost associated with resistant phenotype
Most of Mendel’s theory involved what kind of variation?
Mendelian genetics supported larger DISCRETE variation/ changes.
Define polygenic; what kind of variation do these genes exhibit?
Many traits are affected by many genes simultaneously; Polygenic traits can exhibit continuous variation
Multifactorial inheritance
Inheritance of a polygenic trait
Additive genetic effects
Phenotype of an individual can be determined by summing the effects of each allele that it carries; example: 3 genes involved in the gradation of kernel colors of wheat
Studies found that polygenic traits and continuous variation establish small graded variation is compatible with what?
Mendelian inheritance
Remember natural selection DOESN’T create variation so why in a selected population are there variants?
Variation in a relatively small number of genetic loci can generate an enormous amount of possible phenotypes
What is true when populations contain latent variation?
Not all possible genotypes could be represented
Selection could shift allele frequencies and genetic reassortment could then draw out new phenotypes from pre-existing variation
what is epistasis & give an example
When alleles at two or more loci interact in NON-ADDITIVE
ways to determine phenotype
ex. coat color in oldfield mice; effect of an allele at the Mc1R locus depends on which alleles are present at the Agouti locus
What does it mean when phenotypic effects of loci are Context Dependent? think of old field mouse alleles
Phenotypic effects of alleles at one locus depend on the context that is set by the alleles at another locus
In diploids, when two loci A and B are located on SEPARATE chromosomes…
Alleles will segregate independently according to Mendel’s law
In diploids, when two loci A and B are located on the SAME chromosome…
There is physical linkage; alleles segregate together in the absence of recombination.
What does the rate of recombination depend on?
Depends on the physical distance between the loci; closer together the lower the rate *think of two tied ropes, further apart= more chance for crossing over
Linkage disequilibrium
When there’s statistical associations present between the alleles at the A locus and B locus
How is linkage disequilibrium broken down/ dissipates?
In the absence of other evolutionary processes, linkage disequilibrium is broken down by recombination.
Where does recombination occur?
Occurs between haplotype pairs; creates new haplotypes only in double heterozygotes.
What happens when recombination occurs in a double heterozygote?
New haplotypes are produced
What is the principle of association mapping?
A technique by which loci are responsible for disease or other traits are located
One of the consequences of genetic linkage is Genetic Hitchhiking. What happens during this event?
An unselected or even disadvantageous allele is able to “ride along” with a nearby favorable allele and thus increase in frequency.
What will eventually break the association of Genetic Hitchhiking? What will the speed be dependent on?
Recombination will eventually break this association, but the speed will be dependent on distance.
If recombination breaks down genetic hitchhiking, why do medical diseases still exist?
Genetic diversity for surrounding alleles will be reduced relative to expectations of a neutral model.
What is background selection, (also a consequence of genetic hitchhiking)? analogous to hitch-hiking
Deleterious mutations carry nearby alleles to extinction analogous to hitchhiking.
Alleles can increase in frequency due to selection because…
They directly code for the beneficial mutations or are associated with other beneficial alleles on other loci.
