For allele frequencies to change there has to be: - ANSWERSvariation (there have to be different alleles)
Variation in a population comes from : - ANSWERSMutation
Gene Flow
Once genetic variation has been established, what causes the allele frequencies in a population over generations? - ANS...
organic evolution exam 2 Questions &
Amswers
For allele frequencies to change there has to be: - ANSWERSvariation (there have to
be different alleles)
Variation in a population comes from : - ANSWERSMutation
Gene Flow
Once genetic variation has been established, what causes the allele frequencies in a
population over generations? - ANSWERSNatural selection
Genetic drift
More Gene Flow
Only natural selection causes : - ANSWERSadaptive evolution
Evolution by natural selection involves both ___ and _____ - ANSWERSchance and
"sorting"
New genetic variations arise by chance
Beneficial alleles are "sorted" and favored by natural selection
Natural Selection acts on the _______ not the _______ - ANSWERSPhenotype,
Genotype
phenotypic diversity is affected by : - ANSWERS1. Multiple Genes (=Quantitative traits)
2. Interactions between different genes
3. Trade-offs
example of multiple genes: - ANSWERSwheat color: Three separate genes (A, B and
C)
Independently assorting
i.e., on separate chromosomes
Alleles show incomplete dominance (heterozygote is intermediate between the
homozygotes)
Dominate alleles contribute additively to pigmentation
because of independent assortment and the additive effect of the dominant alleles,
some colors are more common than others
Quantitative Trait - ANSWERSWhen many genes, each behaving individually,
contribute to a phenotypic feature in a cumulative way, the feature is called a
Quantitative Trait
More genes involved in the trait, the more ______ exists - ANSWERSvariation
,Patterns of Natural Selection in Quantitative Characters - ANSWERSDirectional
Stabilizing
Disruptive (=diversifying)
In any species and at any point in time, all three types of selection may be acting.
Directional Selection - ANSWERSPhenotypes at one extreme die off or fail to reproduce
and those at the other extreme leave a higher number of offspring.
This shifts the average frequency distribution towards the favored extreme.
ex.Biston betularia- moths
White phenotype
Dark phenotype
Originally, the vast majority of peppered moths had light coloration. Widespread
pollution - esp. soot - covered the trees and the white moths became more obvious to
predators.
Dark-colored moths flourished because of their ability to hide on the darkened trees.
They left more offspring
Stabilizing Selection - ANSWERSIndividuals with extreme phenotypes die or fail to
reproduce resulting in populations of individuals with intermediate phenotypes.
Most common in stable, unchanging environments where selection has remained the
same for years.
disruptive selection - ANSWERSextreme phenotypes become more frequent from
generation to generation because they survive to reproduce while individuals with
intermediate phenotypes die or fail to reproduce.Diversifying selection results in
polymorphism (two or more different forms are common).
ex.)taurus scarab beetles-one shows head spines the other does not Males with
elaborate horns or antlers may attract more mates but die younger because they are
costly to grow, make the animal clumsy and more obvious to predators. Males without
elaborate horns or antlers attract fewer mates but live longer.
Example of Tracking Natural Selection Affecting Quantitative Traits - ANSWERSUse
survivorship or number of offspring as an approximate measure
ex) beak of finch-
Step 1: Capture weigh, measure, and identify hundreds of the birds and record their
diets of seeds
Step 2: For the seeds the finches eat, measure seed size and seed hardness
Step 3: Identify and count the seeds present on a representative plot
Step 4: Correlate the information with climate data (wet or dry)
Conclusions
Bill size changes incrementally as the environment changes
, Quantitative traits allow organisms to respond more precisely to environmental change
Epistasis - ANSWERSgenes can mask each other's presence or combine to produce an
entirely new trait.
The genes involved in a specific epistatic interaction may still show independent
assortment at the _______level but the ______ ratios may appear to deviate from those
expected with independent assortment. - ANSWERSgenotypic, phenotypic
The Law of Independent Assortment - ANSWERSOriginated by Gregor Mendel
When two or more characteristics are inherited, individual alleles assort independently
during gamete production,
Gives different traits an equal opportunity of occurring together.
Regulatory genes may affect more than one feature
Example heat shock gene Hsp90 (encodes a heat shock protein which helps organisms
cope with stress) - ANSWERS
trade off: - ANSWERSChanging one feature for the better might change another for the
worse.
Pleiotropy: - ANSWERSOne gene Can affect multiple traits
E.g. White cats with blue eyes are usually deaf
A single gene controls pigmentation
pigmentation plays a role in maintaining fluid in ear canals
Antagonistic Pleiotropy: - ANSWERSSelection may act positively for one trait and
negatively for another
in humans, the p53 gene directs damaged cells to stop reproducing, thereby resulting in
cell death. This gene helps avert cancer by preventing cells with DNA damage from
dividing, but it also suppresses the division of stem cells, which allow the body to renew
and replace deteriorating tissues during aging. This situation is therefore an example of
antagonistic pleiotropy, in which the expression of a single gene causes competing
effects, some of which are beneficial and some of which are detrimental to the fitness of
an organism.
Cline - ANSWERSThe pattern of genotypes and phenotypes over a geographical range.
-Step Cline - ANSWERS- each geographical subarea has its own unique adaptations
and dominate phenotypes.
the rat snake, differs markedly in color and pattern over its range.
-Smooth Cline - ANSWERS- the variable phenotypes are not distinct from each other so
that over the geographic range the adaptations blend into each other.
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