Population Genetics

Question 1

How is a breeding value measured?

Answer 1

by PTA (predicted transmitting ability)
or EBV (estimated breeding value)

Question 2

What is the relationship between PTA and EBV?

Answer 2

PTA = 1/2 EBV

Question 3

What is PIN?

Answer 3

profitable index

Kg of milk, fat and protein

Question 4

What is PLI?

Answer 4

profitable lifetime index

combined PTA’s weighted differently - milk, fat, protein, lifespan, SCC, locomotion

Question 5

What is the fertility PTA based on?

Answer 5

calving interval and non-return rate

Question 6

what does a high calving interval mean?

Answer 6

poor fertility - too long to get back into calf again

Question 7

what does a high non-return rate mean?

Answer 7

good fertility - most getting pregnant first time of AI

Question 8

How is robustness PTA measured?

Answer 8

BCS, environmental sensitivity of genes, health, fertility

Question 9

In small animals what are the 4 genetic forces?

Answer 9

• mutation
• migration / outcrossing
• genetic drift and inbreeding
• selection

Question 10

What does an inbred individual have?

Answer 10

An inbred indiviual has identical alleles coming from the same ancestor

Question 11

What is the inbreeding coefficient?

Answer 11

the probability that the 2 copies of the gene are IBD (inherited by descent)

look at probability of inheritance for each allele for each mitotic event

Question 12

What is the problem with inbreeding depression?

Answer 12

can compromise the fitness of the whole line and make some individuals very sick

Question 13

what is ∆F?

Answer 13

change in average inbreeding coefficient over time / generation

the change represents a change in diversity

Question 14

What ∆F is acceptable and why?

Answer 14

less than 0.5% / year - its a decrease in diversity

Question 15

What is Ne?

Answer 15

effective pop’n size

the number of breeding individuals in a hypothetical random mating pop’n that would have the same rate of inbreeding seen in the real pop’n

Question 16

What Ne is wanted?

Answer 16

at least 100 for a fit pop’n

Question 17

What is the relationship between Ne and ∆F?

Answer 17

Ne = 1/2 ∆F

Question 18

What are solutions to inbreeding?

Answer 18

minimise kinship matings
increase no of animals used for breeding
equalise use of males and females
optimise genetic contribution
out-crossing

Question 19

What is a single gene disease?

Answer 19

1 locus

env’t has no effect

Question 20

What is a complex disease?

Answer 20

env’t has an affect and is multi genetic

Question 21

why is genomic EBV better than EBV?

Answer 21

gEBV you can take a swab a few weeks after birth and get accurate results

EBV you dont get accurate results until the animal has offspring to evaluate

Question 22

What is selection intensity?

Answer 22

the difference between the population mean and the mean of the selected individuals - it is the cutoff selected below which individuals are allowed to breed

tougher threshold = faster response ..may be bottlenecking the pop’n though