13: Genetic Resemblance

Question 1

What % of DNA does an individual share with their parents? Great grandparents?

Answer 1

Parents = 50%
Great grandparents = 12.5%

Question 2

Why do we expect relatives to perform alike?

Answer 2

Similar genotypes, developed in similar environment

Question 3

Definition of the ‘relationship’ between relatives

Answer 3

The proportion of genes that two individuals have in common because they are members of the same family

Question 4

What is a common ancestor

Answer 4

An ancestor common to more than one individual or an ancestor common to the parents of an inbred individual

Question 5

Inter vs intraclass

Answer 5

Interclass = relationship between parents and their offspring (two diff generations)
Intraclass = relationship among siblings (same class)

Question 6

What are ancestor relatives? Collateral relatives?

Answer 6

Ancestor relatives are interclass relatives (parent and offspring)
Collateral relatives are intraclass relatives (full or half siblings)

Question 7

Why is genetic resemblance between relatives important in animal breeding?

Answer 7

• estimate variance, covariances, and genetic parameters
• used for genetic selection and breeding methods

Question 8

The amount of phenotypic resemblance among relatives for a trait provides an indication of…

Answer 8

the amount of genetic variation for that trait

Question 9

If the trait has significant genetic basis, the closer the relatives…

Answer 9

the more similar their appearance

Question 10

Two animals are genetically related when

Answer 10

they have at least one common ancestor

Question 11

What is identical by descent?

Answer 11

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

Question 12

What is identical by state? Aka

Answer 12

When alleles are equal (homozygous) but they derive from different animals in the reference population
aka alike in state

Question 13

Second definition of ‘relationship’ between relatives

Answer 13

The probability that a randomly taken allele from individual X is identical by descent to a randomly taken allele from individual Y

Question 14

What is inbreeding

Answer 14

The mating of relatives (animals more closely related than average of pop)

Question 15

Inbreeding causes an increase in the… and a decrease in the…

Answer 15

proportion of loci at which an individual is homozygous

proportion of loci at which an individual is heterozygous

Question 16

Outcomes of inbreeding

Answer 16

Increased homozygosity (alleles IBD)
Increased expression of deleterious recessive alleles
Increased prepotency

Question 17

What is prepotency

Answer 17

The ability of an individual to produce progeny whose performance is especially like its own and/or is especially uniform

Question 18

How does prepotency work

Answer 18

Inbred animals produce fewer unique gametes and therefore fewer unique zygotes leading to low variability in their progeny

Question 19

Examples of the expression of deleterious recessive alleles

Answer 19

Spider leg condition in sheep, dwarfism in cattle

Question 20

Does inbreeding create deleterious recessive alleles?

Answer 20

No, they must already be present in a pop
They just increase expression

Question 21

Expression of deleterious recessive alleles leads to…

Answer 21

reduced fitness (survivability, fertility)

Question 22

What is inbreeding depression

Answer 22

Decrease in the performance of inbred animals due to the expression of unfavorable alleles influencing polygenic traits

Question 23

What is inbreeding depression with regards to quantitative traits

Answer 23

Manifestation of unfavorable gene combination value resulting from increased homozygosity (reduced hybrid vigor)

Question 24

Inbreeding depression and hybrid vigor are functions of…

Answer 24

GCV (NOT BV)

Question 25

The more homozygous gene combinations an individual has, the less its… and ultimately its…

Answer 25

less its gene combination value, its genotypic value and ultimately its performance

Question 26

Inbreeding depression and hybrid vigor are also affected by the…

Answer 26

degree of dominance exhibited at each locus

Question 27

Why do we use inbreeding strategy?

Answer 27

• 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)

Question 28

What is outbreeding? What are the outcomes?

Answer 28

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)

Question 29

Why use outbreeding?

Answer 29

Avoid appearance of inbreeding, cover existence of deleterious recessive alleles
Add hybrid vigor (favourable GCV)
Take advantage of breeding complimentary