Topic 3: Inbreeding

Question 1

What is the most basic definition of inbreeding?

Answer 1

The mating of closely related individuals

Question 2

How do we calculate the number of ancestors?

Answer 2

• 2^t ancestors, where t is the number of generations in the past
• ex. 10 generations, 2^10 = 1024 ancestors

Question 3

Inbreeding will depend on ……

Answer 3

population size

Question 4

“Inbreeding does not directly change the ______ ___ ___ ________, and is therefore not an __________ _________.”

Answer 4

“Inbreeding does not directly change the frequency of an allele, and is therefore not an evolutionary force.”

Question 5

How come inbreeding is not considered an evolutionary force?

Answer 5

• With inbreeding, allele frequency do not change. Inbreeding only increases the frequency of homozygosity in a population
• As evolution is a change in allele frequency over time, these definitions contradict one another.

Question 6

inbreeding affects _________ frequencies, but not _______ frequencies

Answer 6

inbreeding affects genotype frequencies, but not allele frequencies

Question 7

if there is a loop in a pedigree, this is indicative of ______

Answer 7

inbreeding!

Question 8

What is Wright’s coefficient of inbreeding?

Answer 8

• a statistic to estimate the level of inbreeding for a particular individual
• estimates the probability that a specific allele came from a specific ancestor.
• “the probability that two alleles in an individual were both descended from a single allele in an ancestor”

Question 9

What is identity by descent?

Answer 9

• where two alleles that are identical are descended from the same recent ancestral allele
• can be traced back to a common ancestor

Question 10

What is identity by state?

Answer 10

• where two alleles have identical DNA sequences or amino acid sequences
• NOT identical because they have a common ancestor. Just happen to be the same allele (gained separately)

Question 11

What is the difference between identity by descent vs. identity by state?

Answer 11

• identity by descent must have 2 identical alleles that are genetically related, while identity by state has 2 alleles that are identical, but not necessarily related.

Question 12

Alleles that are identical by descent will always be identical in_______, but not all alleles identical by state will be identical by ________.

Answer 12

Alleles that are identical by descent will always be identical in state, but not all alleles identical by state will be identical by descent.

Question 13

How can an inbreeding coefficient increase?

Answer 13

if the common ancestors are also inbred.

Question 14

What hierarchical levels can we measure inbreeding at?

Answer 14

• individual level
• population level

Question 15

describe the individual and population level measuring of inbreeding

Answer 15

individual: measures the extent to which an individual is inbred relative to the random mating in their population. F = the probability that two alleles are identical by descent.

population: measures the average rate of inbreeding in a population relative to random mating. F= proportion of the population that have alleles that are identical by descent

Question 16

How do you calculate the proportion of the population that is NOT inbred?

Answer 16

1 - F (where F = proportion of the population that have alleles that are identical by descent)

Question 17

How would you determine the probability of getting AA alleles (identity by state), and NOT being inbred?

Answer 17

P^2 (1-F)

Question 18

What is outbreeding? what would the inbreeding coefficient be?

Answer 18

• outbreeding occurs when organisms have inbreeding avoidance, such as mammals with complex social structure. Such, the inbreeding coefficient would be less than expected
• F < 0

Question 19

What is random mating? what would the inbreeding coefficient be?

Answer 19

• random mating between individuals, no mate choice
• this is an assumption under Hardy Weinberg
• F = 0

Question 20

What would be the inbreeding coefficient for inbreeding individuals?

Answer 20

F > 0

Question 21

With inbreeding at the population level, F can be defined as…………

Answer 21

With inbreeding at the population level, F can be defined as the rate of reduction in heterozygosity per generation due to inbreeding in a population

Question 22

what is inbreeding depression?

Answer 22

• the decline in fitness ( or traits associated with fitness) that occurs in response to inbreeding.
• typically a reduced health, survival, and fertility of offspring of related individuals

Question 23

inbreeding causes ________ __________which leads to ________________ ___________

Answer 23

inbreeding causes increased homozygosity which leads to inbreeding depression

Question 24

why does increased homozygosity lead to inbreeding depression?

Answer 24

two hypothesis:

• dominance hypothesis: Deleterious recessive alleles are more often expressed when they occur in homozygotes
• overdominance hypothesis: the loss of heterozygote advantage at loci that are homozygous (heterozygosity is more beneficial for individuals)

Question 25

what is “genetic rescue”

Answer 25

• introducing beneficial variation from outside of a population at genes which have a high frequency of variants causing inbreeding depression in the population

Question 26

What is effective population size (Ne)?

Answer 26

• the size of an idealized population showing the same rate of loss of genetic diversity as the real population under study
• the size of an ideal population (i.e., one that meets all the Hardy-Weinberg assumptions) that would lose heterozygosity at a rate equal to that of the observed population.

Question 27

With dog domestication, why has there been an increase in the number of deleterious genetic variants?

Answer 27

As we continue to inbreed dogs to get desired traits, we get inbreeding depression, which is an increase in homozygosity, and Deleterious recessive alleles are more often expressed when they occur in homozygotes

Question 28

Is the French Bulldog an example of a dog breed with less genetic variability? Why?

Answer 28

ASK IN CLASS

Question 29

Did Yordy et al (2020) determine that body size has a greater influence on a dog’s lifespan than inbreeding
depression? How?

Answer 29

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