Topic 5: Non-random Mating Flashcards
assortative mating = ?
any type of mating where mate choice is based on phenotype
non-random gametic union into zygote (can be internal or external of organism, e.g., starfish expelling gametes in water)
positive assortative mating = ?
individuals tend to choose mates that are phenotypically similar to themselves
negative assortative mating = ?
individuals choose mates that are phenotypically unlike themselves
in a randomly mating pop, will some assortative mating occur by chance?
Yes
assortative mating refers to phenotype-based matings that have a higher freq than expected by chance in a randomly mating pop
what are the consequences of assortative mating?
- traits associated with assortative matings are rarely encoded by a single gene, hence usu POLYGENIC
- generally, positive assortative increases homozygosity and negative assortative increases heterozygosity (HW disequil) ONLY for trait-associated genes!
- alters genotype freq, but not allele freq
Is assortative mating a mechanism of evolution? Why/why not?
No, assortative matings alter genotype freq but NOT allele freq
what must we watch out for in assortative mating (traits and genes)
not all traits are gene-based
sympatric divergence/speciation = ?
divergence in the absence of physical barriers
parapatric speciation
occurs when a small pop is isolated, usu at the periphery of a larger group, and becomes differentiated to the point of becoming a new species (physical barrier)
disruptive selection
occurs when both extreme traits are favored in an environments
inbreeding def
- mating between relatives at a higher rate than occurs in a panmictic pop
- increases homozygosity
- heterozygotes deficit
how is inbreeding different from positive assortative mating?
inbreeding increases homozygosity at all loci; assortative mating only involves genes for specific traits
on their own, inbreeding and assortative mating only change genotype freq and do not change ____ ____
allele freq
although inbreeding and assortative mating will not result in pop evolution on their own, what can they influence?
can have important interactions with other agents that can result in evolution
self-fertilization: some organisms have both ___ and ___ _____ –> capable of self-fertilization
male and female gonads (hermaphrodites)
_____ ______ = strongest form of inbreeding
self-fertilization
with continued inbreeding, what happens to heterozygosity, if all individuals in pop are self-fertilizing?
continues until the heterozygosity reaches zero
what happens to F if we keep inbreeding?
increase each generation, converges on 1
do organisms that can self-fertilize usually become completely inbred? what happens?
no, they will usu frequently outcross (F usu does not fully reach 1; no heterozygotes)
inbreeding coefficient will reach an equilibrium value
homozygotes are identical by state. how is this different from identical by descent?
identical by descent:
- two alleles are identical by descent if they arose by replication from the same copy of an allele in an ancestral pop or individual
identical by descent def
two alleles identical by descent if they arose by replication from the same copy of an allele in an ancestral pop or individual
autozygous def
individual that possesses two alleles at a locus that are identical by descent
allozygous def
individual that possesses two alleles at a locus that are not identical by descent (can still be identical by state)
T/F autozygous individuals must also be homozygous
True
T/F allozygous individuals must also be heterozygous
False, they can be homozygous or heterozygous
What probability does F give?
the probability that an individual in pop is autozygous, or has two alleles that are identical by descent
T/F inbreeding increases both homozygosity AND autozygosity
True
T/F in general, anything that increases homozygosity will also increase autozygosity. anything that increases heterozygosity will also increase allozygosity
True
how does inbreeding affect the breakdown of gametic disequil?
since inbreeding decreases heterozygosity over time, it will slow down gametic disequil breakdown rate, because it reduces number of double heterozygotes
what is the basis of inbreeding depression?
inbreeding increases homozygosity -> increases probability that a deleterious recessive allele will occur in a homozygous form
inbreeding depression def
the decrease in a pop’s avg fitness due to manifestation of deleterious recessive conditions in individuals as a result of inbreeding
how is fitness generally defined?
reproductive success (mortality selection, sexual selection, fecundity selection)
in life cycle, when can these occur?
- inbreeding/outbreeding
- natural selection
- migration
- mutation
- genetic drift
- bottleneck
- founder effect
- inbreeding/outbreeding
gametes - natural selection
anywhere - migration
anywhere - mutation
gametogenesis - genetic drift
gametes - bottleneck
anywhere - founder effect
anywhere
what is the genetic rescue effect? what is it for?
genetic rescue effect: an increase in avg population fitness as result of a reintroduction of genetic DIVERSITY
introducing individuals to the threatened population from another population can have a genetic rescue effect and mitigate the effects of inbreeding (and genetic drift)
can we still employ the genetic rescue effect if both populations are suffering from inbreeding depression?
True!
Can inbreeding help purge alleles?
Yes, it can help purge deleterious recessive alleles
outbreeding def, effect
opposite of inbreeding
- individuals mate with non-related individuals with a higher frequency than would occur by chance in a panmictic pop
- increase heterozygosity at all loci (HW disequil)
if H(obs) is greater than H(exp) at all polymorphic loci, we could have?
outbreeding!
why might outbreeding depression happen?
if the populations have local adaptations, which are impaired by outbreeding
T/F anything that results in a heterozygote deficit will result in an “inbreeding coefficient”
True! even if inbreeding may not be the cause
T/F anything that results in a heterozygote excess will result in an “outbreeding coefficient”
True! even if outbreeding may not be the cause
Are any of the following mechanisms of evolution?
- outbreeding
- inbreeding
- assortative mating
No! They do not change allele freq on their own. Can still have important influence when combined with other factors that do change allele freq
