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Flashcards in Chapter 9 Deck (54):

Compensatory mutations

These mutations do not reduce the degree of resistance, but reduce/ eliminate the fitness cost associated with resistant phenotype


Most of Darwin's theory involved what kind of variation?

Continuous variation (gradual change)


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.


______ tends to decrease genetic variation at loci near selected allele.

Natural selection (positive or negative)


Why does hitch-hiking dramatically effect bacteria?

Because they're haploid; and bacterial alleles tend to be close together


Three facts about bacterial alleles/ locus (periodic selection slide)

-do not have recombination between homologous chromosome (haploid)

-no independent segregation of chromosomes

-both of these create a "single" large locus


What is periodic selection?

Result of tight linkage across bacterial genome


What is the process of periodic selection? (4 steps)

New beneficial mutation arises in a bacterial population

Mutation goes into fixation due to natural selection

Selective sweep results: alleles go to fixation due to tight linkage

after fixation, a new advantageous allele arises and the process repeats


What process is possible responsible for the persistence of antibiotic bacteria?

Periodic selection


How is antibiotic resistance transferred?

Through plasmids (small DNA molecules) or transposons


What is effective population size?

The group that has the potential to reproduce (can contribute its fitness to future generations).


What is clonal interference?

Beneficial alleles interfere with one another and slow down selection => competition


Adaptive landscapes (fitness landscapes) shows what?

Interactions among genes; generates a complicated genotype-to-phenotype map.


Why are adaptive landscapes complicated?

-pleiotropy (single gene can effect multiple aspects of phenotype)
-epistasis (phenotypic trait is often determined by complex interactions among multiple genes)
-norms of reactions (single genotype produces different phenotypes in different environments
-dominance (one allele may cover up the effects of another allele at the same locus)
-multiple pathways (a common phenotype may have different genetic basis in different individuals)


Although natural selection act on phenotype...

Next generation only gets genotype.


Quantitative genetics

studying continuously varying traits; ex. tomato size


What are three factors that contribute to phenotype?



-Even if genotypes and environments are identical, there still can be differences


What is developmental noise?

Random chance events during the process of development that can give rise to phenotypic differences



Statistical measure of the variation in a sample; tells us how different trait values are from one another.


Narrow-sense heritability?

Fraction of the total variance due to additive genetic variation


How do we estimate broad sense heritability?

Compare amount of variation among genetically identical individuals with the amount among unrelated individuals ; usually use inbred lines


What is the narrow sense heritability?

A measure of what fraction of the variation is accessible to natural selection... (since natural selection can't possibly act upon all variation, need to look at the fraction of the total variation that is due to additive genetic variation)


Selection Differential (S)

The difference between the mean trait value of the individuals who successfully contribute to the next generation and the mean trait value of all individuals in the population


Selection Response (R)

The difference between the mean trait value of the OFFSPRING population and the mean trait value of the PARENTAL population


Breeder's equation

Expression for mean trait value (average phenotype) of a continuously valued trait that changes over time as a consequence of natural selection

*relates the narrow sense heritability


QTL mapping

way of finding at least the general region of the genome in which QTL, quantitative trait loci, resides (dead science)


Assortative mating

Individuals tend to mate with those of the same genotype/ phenotype


Disassortative mating

Individuals tend to mate with those of different genotypes or phenotypes



Individuals mate with genetic relatives; a type of assortative mating


Identical by descent

Pair of gene copies at a locus that are identical because of shared descent through a recent ancestor; most extreme form is self fertilization = selfing

common in flowering plants



Measures the correlation between two homologous alleles in a single individual; measure of the extent of inbreeding


Inbreeding depression

Occurs when the offspring from matings between genetic relatives have reduced fitness

common when recessive alleles have deleterious consequences on fitness

ex. HTN


If inbreeding increases the frequency of homozygotes, what kind of genes are more likely expressed phenotypically?

Recessive genes