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Midterm

BIOL 1001 Study Guide - Midterm Guide: Allele Frequency, Genotype Frequency, Gene Pool


Department
Biology
Course Code
BIOL 1001
Professor
Tamara Kelly
Study Guide
Midterm

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Learning objectives – midterm 2
LEARNING OBJECTIVES: MICROEVOLUTION
1. Provide arguments supporting evolution as a population process, explaining why individuals
do not evolve. [Comprehension]
Evolutionary change is based on changes in the genetic makeup of populations over time. Populations, not individual
organisms, evolve. Changes in an individual over the course of its lifetime may be developmental (e.g., a male bird
growing more colorful plumage as it reaches sexual maturity) or may be caused by how the environment affects an
organism (e.g., a bird losing feathers because it is infected with many parasites); however, these shifts are not caused
by changes in its genes
2. Justify the importance of genetic variation in populations to the process of evolution,
explaining the ways in which variation is generated. Given a scenario/graph classify: the degree
of variation for that character, variation as qualitative or quantitative. [Comprehension,
Application, Analysis]
Variation is important because it is a strong contributor to evolution. Through variation
within a population individuals vary in genetics. If genotypic, these more advantageous
variation will be favored by natural selection, this resulting in the increase of the
frequency (allele) of these traits. Thus through evolution (microevolution) overtime these
changes can result in it becoming the dominant in the population. Basically without
variation, natural selection would have nothing to favor and pass on (no advantageous
trait) = no evolution (everyone stays the same)
Production of new alleles:  mutations
Rearrangement of existing alleles:  crossing over (during meiosis); Shuffles segments
on the chromosomes  independent assortment (arrangement along metaphase plate);
shuffle whole chromosomes (each homologous pair shuffles independently) random
fertilization between egg and sperm
We display data on quantitative variation in a graph; the width of the curve is propotional
to the variability (amount of variation) amongst individuals.
oA broad, low curve indicates a lot of variation among individuals.
o A high narrow curve indicates little variation among individuals
Quantitative: gradual continuum of variation in a trait. Ex height, weight, skintones, # of
hair
Qualitative: discrete variations in traits, no intermediates. Ex snow geese are either blue
or white
3. Given a scenario (e.g., the number of individuals with a specific genotype), calculate
frequencies of alleles, genotypes, and phenotypes, starting with the number of individuals of a

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specific genotype or phenotype, or the frequency of an allele. Use information as to whether a
population is in HWE to solve a problem. [Application]
Gene pool: the sum of all alleles at all genes loci in all individuals in a population
To describe the structure of a gene pool, scienctists first calculate genotype
frequencies: the percentages of individuals possessing each genotype ECX CRCW= 500
indiv  0.5
CR CR= 450 indiv  0.45 => 0.5+0.45+0.05 =
1
CWCW = 50 indiv  0.05 /1000
Knowing that each diploid organism has two alleles (either two copies of the same or two
different allele ) at each gene locus, a scientist can calculate- Allele frequency: the
abundance of one allele relative to others at the same gene locus with two alleles there
are 3 genotype frequencies (pq, pp, qq (sum of 3 gene frequencies must equal 1), but
only two allele frequencies (p and q (sum of these 2 allele frequencies must equal 1)
EX p= CR(600 x 1) + (450 x 2) + (50 x0) = 1400 / 2000 alleles = 0.7
Q= CW(500 x1)+ (450 x 0 ) + (50 x 2) = 600/ 2000 alleles = 0.3  p+q = 0.7+0.3 =1
Relative abundance: the relative commonness of population within a community
(alleles with genelocus)
Genetic equilibrium: the pt at which neither allele nor genotype frequencies in a
population change in succeeding generations
Loci/locus: a particular gene location on a chromosome  in diploids, each locus has 2
alleles (in diploid organisms ( have 2 pairs of homologous chromosomes) an individuals
genotype includes two alleles at every gene locus)
Fixation/loss: alleles with a frequency of 1 are fixed: lost have frequency of 0
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4. Explain how the Hardy-Weinberg (HW) principle acts as a null hypothesis/model for evolution,
relating the assumptions/conditions of HW to the mechanisms of evolution, and populations to
which HW is applicable. Given a description of a population, indicate whether any (and which) of
the assumptions have been violated. [Comprehension]
The hardy-weinberg principle (is a null model): specifies the conditions under which a
population of diploid organisms achieves genetic equilibrium (the point at which neither
allele frequencies nor genotype frequencies change in succeeding generations)
oNull model since it shows when evolution, which changes allele frequencies,
doesn’t occur
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Reference point in which evaluating circumstances under which evolution
may occur
oP2+2pq+Q2; HW principle acts as a null hypothesis because it demonstrates an
ideal situation where no evolution is occurring (studies that use observational
experiment use this instead of a control variable)
Hw; is a null model that describes the conditions under which microevolution will not
occur:
oNo mutation occurring
oNo gene flow: no emigration or immigration to the gene pool
oRandom mating with respect to the gene in question
oNo genetic drift, or random allele frequency changes, affecting the gene in
question: alleles are drawn in their exact frequency. Not by values caused by
chance
oNo natural selection at the gene in question: population survive and
reproduce equally well
Microevolution will not occur under HW conditions because no new alleles through
mutation, all survive  allele frequency never changes. Thus, can be no change in
genetic makeup of population.
All the above points are mechanisms of evolution and if there is no change in
mechanism of evolution then there is no evolution or change in gene pool frequencies
5. Describe the mechanism of evolution by natural selection, explaining why evolution is not
progressive (i.e., moving towards ‘perfection’), how natural selection is non-random and results
in adaptations. [Comprehension]
Evolution does not progress towards perfection cause evolution operates via chance
occurences. Like mutations and random fluctuations in population, and by natural
selection. Mutations and random events (i.e., a huge volcano explodes and vaproizes a
population indiscriminately) are clearly not progressive events. They’re random.  natural
selction works by creating filter through which the organisms that are most fit, leave the
most offspring. Environments change constantly and since natural selection only
promotes adaptations to the conditions immediately at hand, it is not progressive.
Evolution has no foresight
The genetic variation that occurs in a population because of mutation is random — but selection acts on that variation
in a very non-random way: genetic variants that aid survival and reproduction are much more likely to become common
than variants that don't. Natural selection is NOT random!
Selection occurs based on alleles (traits) they have the more fit, the more likely for the allele to be selected for
(natural selection is not random in that it selects for specific individuals who possess traits advantageous to them
oAdaption: is the accumulation of adaptive traits over time
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