13: Genetic Resemblance Flashcards
What % of DNA does an individual share with their parents? Great grandparents?
Parents = 50%
Great grandparents = 12.5%
Why do we expect relatives to perform alike?
Similar genotypes, developed in similar environment
Definition of the ‘relationship’ between relatives
The proportion of genes that two individuals have in common because they are members of the same family
What is a common ancestor
An ancestor common to more than one individual or an ancestor common to the parents of an inbred individual
Inter vs intraclass
Interclass = relationship between parents and their offspring (two diff generations)
Intraclass = relationship among siblings (same class)
What are ancestor relatives? Collateral relatives?
Ancestor relatives are interclass relatives (parent and offspring)
Collateral relatives are intraclass relatives (full or half siblings)
Why is genetic resemblance between relatives important in animal breeding?
- estimate variance, covariances, and genetic parameters
- used for genetic selection and breeding methods
The amount of phenotypic resemblance among relatives for a trait provides an indication of…
the amount of genetic variation for that trait
If the trait has significant genetic basis, the closer the relatives…
the more similar their appearance
Two animals are genetically related when
they have at least one common ancestor
What is identical by descent?
Both copies of the same gene can be traced back to a single copy in a recent common ancestor
Individual is homozygous at a locus because some of their ancestors were related
What is identical by state? Aka
When alleles are equal (homozygous) but they derive from different animals in the reference population
aka alike in state
Second definition of ‘relationship’ between relatives
The probability that a randomly taken allele from individual X is identical by descent to a randomly taken allele from individual Y
What is inbreeding
The mating of relatives (animals more closely related than average of pop)
Inbreeding causes an increase in the… and a decrease in the…
proportion of loci at which an individual is homozygous
proportion of loci at which an individual is heterozygous
Outcomes of inbreeding
Increased homozygosity (alleles IBD)
Increased expression of deleterious recessive alleles
Increased prepotency
What is prepotency
The ability of an individual to produce progeny whose performance is especially like its own and/or is especially uniform
How does prepotency work
Inbred animals produce fewer unique gametes and therefore fewer unique zygotes leading to low variability in their progeny
Examples of the expression of deleterious recessive alleles
Spider leg condition in sheep, dwarfism in cattle
Does inbreeding create deleterious recessive alleles?
No, they must already be present in a pop
They just increase expression
Expression of deleterious recessive alleles leads to…
reduced fitness (survivability, fertility)
What is inbreeding depression
Decrease in the performance of inbred animals due to the expression of unfavorable alleles influencing polygenic traits
What is inbreeding depression with regards to quantitative traits
Manifestation of unfavorable gene combination value resulting from increased homozygosity (reduced hybrid vigor)
Inbreeding depression and hybrid vigor are functions of…
GCV (NOT BV)
The more homozygous gene combinations an individual has, the less its… and ultimately its…
less its gene combination value, its genotypic value and ultimately its performance
Inbreeding depression and hybrid vigor are also affected by the…
degree of dominance exhibited at each locus
Why do we use inbreeding strategy?
- identify deleterious recessive alleles in a pop
- increase uniformity in a breed (e.g. coat colour)
- increase hybrid vigor by crossing inbred lines or purebred animals (outbreeding)
What is outbreeding? What are the outcomes?
Mating of individuals more distantly related than average for population
Aka crossbreeding
Increases heterozygosity
Masks expression of deleterious recessive alleles
Results in increased GCV (increased hybrid vigor)
Why use outbreeding?
Avoid appearance of inbreeding, cover existence of deleterious recessive alleles
Add hybrid vigor (favourable GCV)
Take advantage of breeding complimentary
