Nonrandom Mating Flashcards
Inbreeding
Mating among genetic relatives
Assortative mating
Similar individuals are more likely to mate than expected by chance (more homozygotes and fewer heterozygotes than expected)
Selfing
A form of inbreeding, mate only with members of the same genotype (aa x aa or AA x AA or Aa x Aa only)
Phenotypic assortative mating
“Likes attract”, type of assortative mating, increase homozygosity just at that gene
Disassortative mating
Dis-similar individuals are more likely to mate than expected by chance (more heterozygotes and fewer homozygotes than expected)
Outbreeding
Avoid mating with genetic relatives, type of disassortative mating
Phenotypic disassortative mating
“Opposites attract”, type of disassortative mating
Identical by descent
When two alleles are identical because both were inherited from a sing copy of that allele in a common ancestor
Inbreeding coefficient (F)
A way to measure inbreeding, the probability that an individual taken at random from a population will have alleles that are identical by descent
Inbreeding depression (delta)
Inbreeding + selection, reduction in fitness of inbred individuals relative to outbred individuals caused by expression of deleterious recessive alleles in homozygous genotypes
Purging
The removal of deleterious alleles by selection, inbreeding benefits since it can remove deleterious alleles when they become present in homozygotes
Nonrandom mating affect in allelic diversity and frequencies
Acting alone does not change allelic frequencies (not a mechanism of evolution) but rather changes genotype frequencies, decrease heterozygosity and thus decreases allelic diversity
Mechanism of evolution?
No
Affect on genotype frequencies
Changes them
Assortative mating affect on genotype
Decrease in heterozygosity
Disassortative mating affect on genotype
Increase heterozygosity
Violate Hardy-Weinberg equilibrium principle?
Yes
Inbreeding affect on genotype
More homozygotes and fewer heterozygotes than expected
Inbreeding alone affect allelic frequencies?
No, affects genotype frequencies only
Calculate F
Use H = 2pq(1-F) where 2pq is the expected frequency of heterozygotes in a population with ransom mating at H-W eq and F is the fractional reduction in heterozygosity in an inbred population compared with a randomly mating population, high F means high levels of inbreeding (closer to 1)
Range of F
0-1
High vs low F
High F means higher inbreeding meaning that heterozygosity is decreased significantly and homozygotes are in excess relative to H-W, low F means lower inbreeding meaning heterozygosity and homozygous numbers are relatively normal in relation to H-W
Two processes involved in inbreeding depression
Inbreeding and selection
Inbreeding depression genetic explanation
An excess number of homozygotes are produced and homozygotes might have different fitness from heterozygotes, recessive deleterious alleles (normally hidden in heterozygotes) can come together in homozygous inbred offspring and be expressed
Calculate inbreeding depression (delta)
Delta = 1-(wi/wo) where wi is the fitness of inbred individuals and wo is the fitness of outbred individuals
Factors affecting inbreeding depression
- Environmental stress - more severe under stressful situations
- Stage of life cycle - effects may only show later in life
- Degree of inbreeding - selling > sibling > cousin
- Current frequencies of deleterious alleles in family or population
Long term inbreeding
Populations that have been inbreeding/selfing for a long time have less inbreeding depression since selection had already purged deleterious alleles and so they are no longer hidden in a heterozygous state
Purging and allele frequencies
Over time purging reduces magnitudes of inbreeding depression by removing deleterious recessive alleles, if inbreeding occurs for a long time population may no longer feel any negative effects
How organisms avoid inbreeding depression?
Outbreeding and disassortative mating through mate choice, genetically controlled self comparability and dispersal, small inbreeding populations may not be able to avoid (conservation concern)
Phenotypic assortative mating changing genotype frequencies
Based on underlying genotype similarity this can also lead to an increase in homozygotes for that trait
