Mating Systems Flashcards
What are the two types of mating?
random and non-random
What do genotypic frequencies depend on?
-genotypic frequencies depend on allelic frequencies
What is non-random mating used for? (strategies for)
strategies for genetic change
What are two strategies used by breeders for genetic change?
selection and mating systems
What is selection?
deciding which individuals to retain as parents
How does selection affect genes?
parents contribute genes to subsequent generations
What are the goals of selection?
increase the frequency of alleles with desirable effects and decrease the frequency of alleles with undesirable effects
What is mating systems?
which males are mated to which females
What does the application of mating systems lead to?
alters genotypic frequencies
Do mating systems alter allelic frequencies?
no
What is random mating by breeders?
no attempt by breeder to pair specific mates
What is non-random mating in terms of Hardy Weinberg?
expected proportion of homozygous and heterozygous individuals deviate from H-W expectations
What is random mating in terms of Hardy Weinberg?
any mate can mate with any female, required for Hardy Weinberg Equilibrium
What is assignment of mates based on?
genetic relationship and phenotypic similarity
What is genetic relationship?
how close or how distantly related the animals are
What is phenotypic similarity?
how close or different the animals look phenotypically
What are the two types of mating based on genetic relationship?
inbreeding and outbreeding
What does inbreeding result in?
increase in homozygosity beyond what would be found in randomly mating population
What does outbreeding result in?
increase in heterozygosity, hybrid vigor
What are the two types of mating based on phenotypic relationship?
positive assortative mating and negative assortative mating
What are examples of positive assortative mating?
Tall x Tall. Red x Red
What are examples of negative assortative mating?
Tall x Short, Red x Black
What is genetic relationship based on?
pedigree
What is inbreeding?
more closely related
What is outbreeding?
less closely related
What is inbreeding coefficient represented by?
Fx
What is inbreeding coefficient?
- probability that 2 alleles at a locus in an individual are identical by descent
- reflection of the increased proportion of homozygous loci in an individual
What is outbreeding mainly used in?
commercial meat production
What is phenotypic similarity based on?
performance
What is positive assortative mating?
resemble one another closely
What is negative assortative mating?
resemble one another less closely
What is the goal of mating systems?
alter genotypic frequencies
What increases homozygosity?
inbreeding and positive assortative mating
What increases heterozygosity?
outbreeding and negative assortative mating
The more closely related two animals mated are…
the more severe the inbreeding
How are the sire and dam related in inbreeding?
genetically
How does inbreeding affect phenotype and performance?
depression in phenotype and decrease in performance
What does Fx measure?
the percent increase in homozygous gene pairs in the individual relative to the average of the breed
If an individual has an Fx of 0.25, what does this tell you?
25% of genes are similar to a particular ancestor
What is Fx value like for most herd of livestock?
not more than 0.5
In arrow diagrams for inbreeding, what does each arrow leading away from an individual represent?
a Mendelian segregation of genes
In general what is a common ancestor?
ancestor common to more than one individual
In terms of inbreeding what is a common ancestor?
an ancestor common to parents of an inbred individual
How are genes described?
genes are identical by descent
What type of alleles can be involved in inbreeding?
alleles “alike in state” (same allele HH, but not traceable to a common ancestor)
What is IBD?
(gene is) identical by descent
What is IBD also known as?
alleles “alike in state”
What is linebreeding?
a less intense version of inbreeding
What is linebreeding?
mating individuals within a particular line, concentrating genes of one common ancestor
What is linebreeding designed to do?
maintain a substantial degree of relationship to highly regarded ancestor
What is linebreeding used in?
horse industry
What are the 6 effects of inbreeding?
- Prepotency
- Expression of deleterious recessive alleles
- Inbreeding Depression
- Tends to “fix” characteristics (traits) in a population
- Concentrate genes
- Increase probability of getting similar genes to offspring from ancestor
What is prepotency?
the degree to which an animal will pass their characteristics consistently
What is prepotency in terms of performance?
performance of offspring is like that of the parents
What does prepotency attempt to do?
make individuals more homozygous for superior genes
What does inbreeding not increase?
does not increase frequency of detrimental alleles
What does inbreeding not create?
does not create deleterious recessive alleles
How does inbreeding affect deleterious recessive alleles?
increases expression
What is inbreeding depression?
decrease in performance of inbreds for traits like fertility and survivability; unfavorable gene combination value
What type of traits does inbreeding depression affect?
quantitative/polygenic traits
How does inbreeding depression affect polygenic traits?
individual effects on genes are small, but taken together can decrease performance
What is poor gene combination value a result of?
increased homozygosity
What does gene combination value cause a change in?
genotypic frequency
How does inbreeding depression affect quantitative traits?
unevenly
What type of quantitative traits are affected by inbreeding depression?
repro & health, production traits, and product quality traits
How are repro and health traits affected by inbreeding depression?
seriously
How are production traits affected by inbreeding depression?
moderately
How are product quality traits affected by inbreeding depression?
little affected
How are genes concentrated as a result of inbreeding?
good and bad
Who discovered how to measure inbreeding?
Sewell Wright
What is the formula for calculating inbreeding?
Fx=Σ(1/2)^n+1 (1+FA)
What is Fx?
inbreeding coefficient of individual X
What does n represent in the inbreeding formula?
number of segregations of genes (matings) between common ancestor(s) and sire and dam of X
What is FA?
inbreeding coefficient of common ancestor
If there is no common ancestor what is Fx?
0
What is additive genetic relationship?
proportion of genes which 2 individuals have in common
What does additive genetic relationship describe?
the added genetic likeness of the 2 individuals in question
How is additive gene relationship shown?
numerical value, 0-1
What kind of genetic relationship do cattle have?
all cattle have a large proportion of genes in common.
What does genetic relationship attempt to quanitify?
the proportion of genes within 2 individuals that are identical by descent
How can individuals inherit genes?
- a descendant may have inherited gene from the other, an ancestor
- both individuals may have directly inherited the gene from an ancestor to whom both were related
explain meaning of numerical bounds of additive genetic relationship?
0 (no genes identical by descent) - 1 (all genes identical by descent)
What is the relationship of x and y represented by?
Rxy
