Topic 5: Non-random Mating

Question 1

assortative mating = ?

Answer 1

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)

Question 2

positive assortative mating = ?

Answer 2

individuals tend to choose mates that are phenotypically similar to themselves

Question 3

negative assortative mating = ?

Answer 3

individuals choose mates that are phenotypically unlike themselves

Question 4

in a randomly mating pop, will some assortative mating occur by chance?

Answer 4

Yes

assortative mating refers to phenotype-based matings that have a higher freq than expected by chance in a randomly mating pop

Question 5

what are the consequences of assortative mating?

Answer 5

• 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

Question 6

Is assortative mating a mechanism of evolution? Why/why not?

Answer 6

No, assortative matings alter genotype freq but NOT allele freq

Question 7

what must we watch out for in assortative mating (traits and genes)

Answer 7

not all traits are gene-based

Question 8

sympatric divergence/speciation = ?

Answer 8

divergence in the absence of physical barriers

Question 9

parapatric speciation

Answer 9

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)

Question 10

disruptive selection

Answer 10

occurs when both extreme traits are favored in an environments

Question 11

inbreeding def

Answer 11

• mating between relatives at a higher rate than occurs in a panmictic pop
• increases homozygosity
• heterozygotes deficit

Question 12

how is inbreeding different from positive assortative mating?

Answer 12

inbreeding increases homozygosity at all loci; assortative mating only involves genes for specific traits

Question 13

on their own, inbreeding and assortative mating only change genotype freq and do not change ____ ____

Answer 13

allele freq

Question 14

although inbreeding and assortative mating will not result in pop evolution on their own, what can they influence?

Answer 14

can have important interactions with other agents that can result in evolution

Question 15

self-fertilization: some organisms have both ___ and ___ _____ –> capable of self-fertilization

Answer 15

male and female gonads (hermaphrodites)

Question 16

_____ ______ = strongest form of inbreeding

Answer 16

self-fertilization

Question 17

with continued inbreeding, what happens to heterozygosity, if all individuals in pop are self-fertilizing?

Answer 17

continues until the heterozygosity reaches zero

Question 18

what happens to F if we keep inbreeding?

Answer 18

increase each generation, converges on 1

Question 19

do organisms that can self-fertilize usually become completely inbred? what happens?

Answer 19

no, they will usu frequently outcross (F usu does not fully reach 1; no heterozygotes)

inbreeding coefficient will reach an equilibrium value

Question 20

homozygotes are identical by state. how is this different from identical by descent?

Answer 20

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

Question 21

identical by descent def

Answer 21

two alleles identical by descent if they arose by replication from the same copy of an allele in an ancestral pop or individual

Question 22

autozygous def

Answer 22

individual that possesses two alleles at a locus that are identical by descent

Question 23

allozygous def

Answer 23

individual that possesses two alleles at a locus that are not identical by descent (can still be identical by state)

Question 24

T/F autozygous individuals must also be homozygous

Answer 24

True

Question 25

T/F allozygous individuals must also be heterozygous

Answer 25

False, they can be homozygous or heterozygous

Question 26

What probability does F give?

Answer 26

the probability that an individual in pop is autozygous, or has two alleles that are identical by descent

Question 27

T/F inbreeding increases both homozygosity AND autozygosity

Answer 27

True

Question 28

T/F in general, anything that increases homozygosity will also increase autozygosity. anything that increases heterozygosity will also increase allozygosity

Answer 28

True

Question 29

how does inbreeding affect the breakdown of gametic disequil?

Answer 29

since inbreeding decreases heterozygosity over time, it will slow down gametic disequil breakdown rate, because it reduces number of double heterozygotes

Question 30

what is the basis of inbreeding depression?

Answer 30

inbreeding increases homozygosity -> increases probability that a deleterious recessive allele will occur in a homozygous form

Question 31

inbreeding depression def

Answer 31

the decrease in a pop’s avg fitness due to manifestation of deleterious recessive conditions in individuals as a result of inbreeding

Question 32

how is fitness generally defined?

Answer 32

reproductive success (mortality selection, sexual selection, fecundity selection)

Question 33

in life cycle, when can these occur?
- inbreeding/outbreeding
- natural selection
- migration
- mutation
- genetic drift
- bottleneck
- founder effect

Answer 33

• inbreeding/outbreeding
  gametes
• natural selection
  anywhere
• migration
  anywhere
• mutation
  gametogenesis
• genetic drift
  gametes
• bottleneck
  anywhere
• founder effect
  anywhere

Question 34

what is the genetic rescue effect? what is it for?

Answer 34

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)

Question 35

can we still employ the genetic rescue effect if both populations are suffering from inbreeding depression?

Answer 35

True!

Question 36

Can inbreeding help purge alleles?

Answer 36

Yes, it can help purge deleterious recessive alleles

Question 37

outbreeding def, effect

Answer 37

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)

Question 38

if H(obs) is greater than H(exp) at all polymorphic loci, we could have?

Answer 38

outbreeding!

Question 39

why might outbreeding depression happen?

Answer 39

if the populations have local adaptations, which are impaired by outbreeding

Question 40

T/F anything that results in a heterozygote deficit will result in an “inbreeding coefficient”

Answer 40

True! even if inbreeding may not be the cause

Question 41

T/F anything that results in a heterozygote excess will result in an “outbreeding coefficient”

Answer 41

True! even if outbreeding may not be the cause

Question 42

Are any of the following mechanisms of evolution?

• outbreeding
• inbreeding
• assortative mating

Answer 42

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