4C Flashcards
what is evolutionary process
how do this process occur?
The evolutionary process= Changes in the proportion of different variants
Phenotype ->(drift, natural selection)-> Reproductive
Success (fitness)->Genes
->Mutation-> phenotype (its like a triangle)
BY GENETIC DRIFT
can affect the frequencies of
genetic variants and traits during life cycle,
especially mating and survival
RAndom processes
From an evolutionary perspective, such events will
be random if their probability of occurrence is not
affected by an individuals’ ______________
phenotype
Genetic drift
What is it and what causes it?
- Changes in allele frequency due to chance (“sampling error”) in finite
populations, especially very small population
The consequences of random processes are
more significant for _____ ______ than for
______ population
small populations than for large populations
Genetic drift causes _______ in finite populations
evolution
Genetic drift results from …
random sampling error and sampling error
is higher with a smaller sample
The consequences of ______ ______ are more significant for
small populations than for large
populations
random processes
the consequence is
fixation or extinction of a allele
Genetic drift ______ genetic variation in a population
reduces
What is bottlenecks
temporary reductions in population size cause drift, reduce
genetic variation, and cause genetic differences between populations –
significant conservation implications
Founder effect
cause genetic drift, new populations started by a small number of individuals that left
in southeast asia
humans interbreed with denisovans 50000 yrs ago
what is phylogeny?
who do all non africans descend from
what reflects founder effect?
Phylogeny: human populations closely
related to neighbours.
* All non-Africans descend from a small
population of humans who lived in
Ethiopia.
* Decline in genetic diversity reflects
founder effects
Nature of genetic drift results in changes in __________ ________, even if the initial
frequencies are ___ ____
,allele frequences , the same
Key concepts:
Genetic drift causes reductions in ______ ______ - variation is lost more
rapidly in ____ populations (bottlenecks and founder events)
Genetic drift causes population ______
genetic variation, small, divergence
Interbreeding
Does interbreeding violate or agree with HWE assumptions?
what causes it?
A special case of nonrandom mating (e.g. a violation of HWE
assumptions)
interbreeding have consequences fro the overall fitness of the population
* What causes it?
– Small populations (absolute, geographic or cultural)
– Mating system (mating with relatives, ie cousins
Non random mating -
interbreeding -
outbreeding-
assortative mating -
Mating individuals are more closely related or less closely related than those drawn
by chance from a random mating population
* inbreeding - mating with relatives
* outbreeding - mating with individuals more distantly related (i.e. non-relatives)
* assortative mating - individuals with similar genotypes and/or phenotypes mate
with one another more frequently than would be expected under a random mating
pattern (e.g., body size)
Although inbreeding affects _____ frequencies, it does not ….
genotype frequencies, alter allele frequencies, by itself:
example: self-crosses- ultimate source of interbreeding
results in reduced fitness
Interbreeding depression
What is interbreeding depression?
Rare deleterious alleles more likely to combine in homozygotes
(expression of homozygous recessives
If you self, a greater proportion of your offspring are ___________than the
proportion from individuals that outcross
Nonrandom mating changes _______ frequencies
* Depending on the amount of genetic variation, this could produce_______ ___________ at many loci in your offspring
Selection acts on ____________
* If a significant proportion of mutations are _________, these will be expressed…
A greater proportion of your offspring will have _____ _______ than expected with
______ mating
If you self, a greater proportion of your offspring are homozygous than the
proportion from individuals that outcross
Non random mating changes genotype frequencies
* Depending on the amount of genetic variation, this could produce homozygous
recessives at many loci in your offspring
Selection acts on phenotypes
* If a significant proportion of mutations are deleterious, these will be expressed…
A greater proportion of your offspring will have lower fitness than expected with
random mating
Natural selection
a predictable change in the frequency distribution of a trait between the parental and
offspring generations as a result of three conditions:
1)Individuals vary
2) Survival and reproduction are not random
3) Variation is passed on to offspring (Inheritance)
1
Evolution in response to natural selection is ________ when these conditions are met
* Results in Differential propagation of different genotypes
* Specific features of the environment can generate natural selection on a trait
What are its effects?
* ________ of one allele/_____ of genetic variation
* Maintenance of _______ _______
Evolution in response to natural selection is inevitable when these conditions are met
* Results in Differential propagation of different genotypes
* Specific features of the environment can generate natural selection on a trait
What are its effects?
* Fixation of one allele/loss of genetic variation
* Maintenance of genetic variation
- Analyzing change in frequency of traits in a population:
- Three patterns emerge:
– directional selection
– stabilizing selection (and balancing selection)
– disruptive selection
directional selection:
stabilizing selection
disruptive selection
directional Selection: Individuals of one extreme phenotype favoured
* Stabilizing Selection: Individuals with intermediate phenotype favoured,
extreme phenotypes selected against.
* Disruptive Selection: Both extreme phenotypes favoured; intermediate
phenotypes selected against
Modes of selection: no selection
When condition 2 does not hold,
selection cannot proceed, what the condition 2?
2 conditions= (survival and reproduction are not random)
modes of selection: directional
Evolution of the trait mean (at least). Occurs
when…
Evolution of the trait mean (at least). Occurs
when fitness varies positively or negatively
with “trait” size
Stabilizing selection
Variance decreases between generations, but
the trait mean does not change
-Average individuals have higher fitness than
extreme individual
Stabilizing Selection:
- ____________ advantage
-Single amino acid substitution leads to….
-________ allele A(normal), S(sickle)
*Heterozygote advantage
*Example: Sickle cell anemia and malaria
*Single amino acid substitution leads to
crystallization of hemoglobin at low
oxygen concentrations
*Co-dominant alleles-BUT I THOUGHT THIS WOULD BE INCPMPLETE DOM BASED ON THE OG DEFITION HE GAVE US?????
A (normal), S (sickle)
Heterozygotes AS have mild condition,
homozygote SS often don’t surviv
-Malaria caused by …
* Individuals “normal” (AA) at the sickle cell locus get ______ ____ ______,
heterozygotes ____ ____, blood cells sickle ……
malaria caused by Plasmodium falciparum (a protist) that also infects
red blood cells
* Individuals “normal” (AA) at the sickle cell locus get very bad malaria,
heterozygotes less bad, blood cells sickle slowing population growth of
protist
Disruptive selection
Both extreme phenotypes favoured; intermediate
phenotypes selected against
Average individuals have lower fitness than extreme individuals
Drift and Selection : Natural selection is more
powerful in large populations because
Drift weaker in large populations
Small advantages in fitness can lead to large changes over the long term
- Viability selection:
- Fecundity selection:
- Viability selection: differences in survival
- Fecundity selection: differences in reproductive succes
Gametes-
males -
females-
Gametes!!
* Males produce abundant, energetically cheap, and more motile sperm
* Females produce few, energetically expensive, and less motile egg
sexual monomorphism-
sexual dimorphism-
The Evolution of Sexual Dimorphis, reproductive success = ____ + _____
reproductive success = fecundity + mating success
The evolution of sexually dimorphism -
natural selection : inevitable outcome when three conditions occur together;
variation, fitness differences and inheritance.
Fitness differences: involve at least one of mating ability, fertilizing ability, fertility and/
or survivorship
Sexual selection broader than Darwin’s conception of natural selection: result of
heritable differences in fertility and/or survival
In contrast, Darwin considered selection that arose because of mating ability or
fertilizing ability as a different process, sexual selectio
natural selection : inevitable outcome when three conditions occur together;
variation, fitness differences and inheritance.
Fitness differences: involve at least one of mating ability, fertilizing ability, fertility and/
or survivorship
Sexual selection broader than Darwin’s conception of natural selection: result of
heritable differences in fertility and/or survival
In contrast, Darwin considered selection that arose because of mating ability or
fertilizing ability as a different process, sexual selection
is sexual selection different
Darwin realized many of the traits produced by sexual selection often diminish survival.
The modern perspective actually incorporates sexual selection as part of natural
selection, recognizing that the process does not differ, but the outcomes may
what are 2 types of sexual selection
Sexual selection results from either or both of two components of mating:
1) Intrasexual selection: fitness differences resulting
from differing abilities of members of the same sex
to compete for mating opportunities (i.e. male-male
competition)
2) Intersexual selection: fitness differences resulting
from preferential mating between specific males and
females (i.e., mate choice)
What are differences in parental investment?
What is reproductive success?
Differences in parental investment
– gamete production
– eggs are expensive, sperm is cheap
– in any species, more sperm than eggs are produced
– parental care
– cost of bearing (pregnancy) & raising offspring
– usually greater in females, but exceptions exist
* Reproductive Success: Females are limited by resources, males are limited by
access to females (usually
