Genetics Flashcards
(22 cards)
What is heritability?
the proportion of variation in a trait that is controlled by genes
What is a breeding value (BV)?
A statistical measure of all genes that affect a trait
What is the average breeding value for a population?
zero
What is the breeding value for an animal without any information?
one half of the BV from each parent
What is a selection index?
The sum of breeding values (for different traits), weighted by their importance
What is the difference between simple and complex inheritance?
- simple: one or a few genes
- complex: many genes
What are the steps for selection?
- select best breed for the goal/desired change
- select the best parents (based on an estimate of genetic merit)
- measure the change and repeat these steps
How is heritability measured?
- 0 to 1
- low heritability allows slow genetic change
- high heritability allows rapid genetic change
What changes due to culling and deaths?
A flock/herd has more young stock than old stock
How can genetic gain be calculated?
intensity of selection x accuracy of selection x genetic variance
divided by generation interval (age when progeny are born)
What are the steps to make genetic progress in sheep?
- 1: decide what traits are important
- 2: choose breed(s)
- 3: choose rams
What are maternal traits?
- number of lambs
- ewe size
- GHG emissions
- wool
- disease/parasite resistance
What are terminal traits?
- growth traits
- carcass weight
- meat traits
Are maternal traits important for genetic selection?
Only if the progeny are being retained for further breeding
What are some of the maternal breeds of sheep?
- Romney
- Merino
- Perendale
- Coopworth
- composites
What are some of the terminal breeds of sheep?
- Suffolk
- Texel
- Poll Dorset
- composites
What do the large amount of traits in sheep affect?
revenue and costs
What are the steps to make genetic progress in dairy cows?
- 1: decide on traits/goals
- 2: choose breed(s)
- 3: choose AI or natural mating
- 4: choose AI company
- 5: choose “bull of the day” (most common) or specific bulls
What are the most common sought after traits in dairy cows?
- milk production
- disease traits
- conformation traits
- feed efficiency
What are the primary cow breeds in NZ?
- Holstein-Friesian
- Jersey
- Kiwicross
What are the difference between Holstein-Friesians and Jerseys?
- Jersey is smaller
- Holstein-Friesian produces higher milk volume
What are the ten traits under the Dairy National Breeding Objective (NBO)?
- milk volume
- milk protein
- milk fat
- fertility
- gestation length
- liveweight
- somatic cell score
- body condition score
- functional survival
- udder overall
