Biology 1001A Study Guide - Final Guide: Genotype Frequency, Allele Frequency, Frequency-Dependent Selection

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Published on 20 Apr 2013
School
Western University
Department
Biology
Course
Biology 1001A
Professor
Bio 1001 Final Exam Outcomes
Lecture 12 Inheritance in Populations
Strategy to distinguish between a phenotype that results from
codominance relative to incomplete dominance
o Incomplete dominance occurs when effects of recessive alleles can
be detected to some extent in heterozygotes (red + white =pink)
o Codominance occurs when effect of different alleles are equally
detectable in heterozygotes (red + white = spotted)
o Cannot distinguish in inheritance patterns, they are the same
Characteristics that identify a pleiotropic allele
o When two or more characters are affected by a single gene
Conditions under which Hardy-Weinberg Equilibrium is possible in a
population
o Genetic equilibrium (allele and genotype frequencies do no change)
occurs when: no mutations, no gene flow, large population size, no
selection, and random mating
o Evolution is not occuring under these conditions
General pathway of eukaryotic membrane protein production
o DNA is transcribed in nucleus ribosomes transport transcripts to
ER ER translates proteins are packaged into vesicles to the
Golgi complex send protein to cell membrane
General physiology of skin / hair pigmentation
o Pigment production is determined by melanocytes that produce
melanin melanosomes that exported into cells
o Two kinds of melanin black VS red & yellow, brown is produced
by the mixture of the two
Characteristics of dominant alleles
o Mask effects of recessive alleles and determine phenotype
o An allele is not always dominant all the time, depends on other
Which allele in a heterozygote is dominant, given biochemical mechanism
of action of allele products
o Happens due to interaction of the gene products
Factors that affect how allele frequencies change over time in a population
o No selection = allele frequencies do not change
o Diploidy, dominance / recessive relation, inheritance are not in
themselves sufficient to drive changes in allele frequencies
Allele frequencies (p and q), given genotypic frequencies
o p2 + 2pq + q2 = does not have to be 50/50
Function of various MC1R alleles
o Membrane receptor that produce black melanin if there are high
cyclic AMP levels and red during low levels (due to hormones)
o B allele (always on), W allele, R allele (always off)
Lecture 13 Selection & Fitness
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Meaning of deme, population, allele frequency, genotype frequency
o Deme: local population of organisms of one species that interbreed
with one another and share distinct gene pool
o Population: group of potentially interbreeding organisms
o Allele Frequency: proportion of different alleles within a population
o Genotype Frequency: frequency of genetic constitutions within a
population
Allele frequencies in a population, given the genotype frequencies
o Frequency of genotypes: f(pp) = p2, f(pq) = 2pq, f(qq) = q2
Genotype frequencies in the next generation, given the allele frequencies
and assuming Hardy-Weinberg equilibrium
o If population is at genetic equilibrium of locus p and q, predicted
frequency are p2, 2pq, q2
Assumptions of the Hardy-Weinberg equilibrium
o No evolutionary forces, genes on separate chromosomes, at least 2
alleles, large effective population size, and no inbreeding
Conditions necessary for Hardy-Weinberg equilibrium
o Large population, random mating, no gene flow or selection
Whether a population is in HWE, given observed genotype or phenotype
frequencies
o Compare actual observed frequency with predicted HWE frequency
o If they are not equal, population may be evolving
Effect on selection on changes in allele frequency
o Can cause genotypic frequencies in a population change as one
genotype is weeded out, brings population out of HWE
Relative VS absolute fitness
o Relative Fitness (w): fitness of genotype relative to other genotypes
in a population, predicts genotype change
o Absolute Fitness (W): number of offspring / survival rates /
lifespan…etc produced by a certain genotype
How to calculate relative fitness
o w = W / WMAX
o Fittest genotype = 1, range between 0 1
How to quantify strength of selection
o Greater the difference in between other genotypes, stronger the
selection and faster the evolution
Relationship between dominance / recessiveness of alleles and response
to selection
o Selected against (dominant) disappear from population, quickly
weeded out
o Selection for (dominant) spreads quickly but never reaches 1
o Selected against (recessive) remain at low frequencies
indefinitely, masked by dominant in heterozygotes
o Selected for (recessive) takes a while to spread but may
completely outcompete dominant partner
Effect of heterozygote advantage on genetic variation
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o Increases number of heterozygotes in population, does not weed
out homozygotes
o Selection is occurring (population is out of HWE) but no evolution
Why amount of genetic variation in a population is important
o Raw material for evolution to occur, without it there can be no
adaption to a changing environment
o Inbreeding Depression: offspring of close relatives tend to have low
fitness since deleterious recessive alleles are more likely to
combine in offspring
Different types of selection (stabilizing, directional) and their effect on
genetic variation
o Vast majority of traits exhibit continuous quantitative variation
o Stabilizing: extreme phenotypes are selected against, reducing
amount of variation (most common)
o Directional: extreme phenotype is selected for, shifts mean of
population in that direction, eventually becomes stabilizing
o Disruptive: extreme phenotype on either side of the distribution,
intermediates selected against, splitting distribution in two
Lecture 14 Selection VS Other Evolutionary Forces
Difference between Batesian and Mullerian mimicry
o Batesian: palatable species mimic distasteful models are protected
against predators (frequency-dependent)
o Mullerian: mimicry between different species benefits both, predator
learns warning pattern that applies to all potential distasteful prey
How population frequency of a mimic phenotype may affect its fitness
o Batesian more frequent the mimic and less frequent the model,
the greater chance the predators will attack the mimic
o Mullerian rare conspicuous warning patterns on unpalatable
individuals offer little protection
Why same phenotype may be selected against in one environment but
have a selective advantage in different environment
o Population sufficiently widespread enough may maintain a variety
of genotypes, each of which is superior in a particular habitat
Meaning of genetic load and genetic death
o Genetic Load: extent to which population departs from optimal
genotype
o Genetic Death: loss of some individuals through any means that
reduces reproductive ability
o Population with a relatively high genetic load may find an
environment where previously detrimental alleles may benefit
survival
Effect of various types of selection on amount of variation in a population
o Stabilizing selection causes less variation
o Not all population experience directional selection over the same
time
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Document Summary

Strategy to distinguish between a phenotype that results from codominance relative to incomplete dominance. Characteristics that identify a pleiotropic allele: when two or more characters are affected by a single gene. General pathway of eukaryotic membrane protein production: dna is transcribed in nucleus ribosomes transport transcripts to. Er er translates proteins are packaged into vesicles to the. Golgi complex send protein to cell membrane. Characteristics of dominant alleles: mask effects of recessive alleles and determine phenotype, an allele is not always dominant all the time, depends on other. Which allele in a heterozygote is dominant, given biochemical mechanism of action of allele products: happens due to interaction of the gene products. Factors that affect how allele frequencies change over time in a population: no selection = allele frequencies do not change, diploidy, dominance / recessive relation, inheritance are not in themselves sufficient to drive changes in allele frequencies.

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