3 Domestication, Breeding and Genetics Flashcards
(19 cards)
What is the definition of inbreeding in genetics?
Mating of individuals more closely related than the population average, aiming to increase the frequency of favourable alleles.
What are the genetic effects of inbreeding on a population?
Decreased heterozygosity
Increased homozygosity
Greater expression of deleterious recessive alleles (e.g., arachnomelia)
Loss of genetic diversity
What is heterosis (hybrid vigour) in contrast to inbreeding depression?
It’s the improved performance in offspring from genetically diverse parents, showing opposite effects to inbreeding depression.
What is inbreeding depression and what traits are affected?
Reduced performance in fitness-related traits such as reproduction, disease resistance, and vigour due to unfavourable homozygosity in polygenic traits.
How is the inbreeding coefficient (F) calculated and interpreted?
F =(½) n
, where n is the number of individuals in the pathway to a common ancestor.
It represents the probability that both alleles at a locus are identical by descent.
What factors influence the rate of inbreeding (ΔF)?
Breeding male-to-female ratio
Variation in family size
Population size and fluctuations
What is the ideal acceptable rate of inbreeding (ΔF) per year?
deally less than 0.5% per year, and definitely under 1%.
Name three methods to reduce inbreeding
Increase breeding population size
Limit number of offspring per parent
Use structured mating systems (e.g., factorial or circular m
Why is managing inbreeding important in closed populations?
Because inbreeding is unavoidable in closed populations, it must be balanced with selection intensity to maintain long-term genetic gain and population health.
What is heterosis (hybrid vigour)?
It’s the superior performance of F1 crossbred animals compared to the average of their purebred parents.
How is heterosis related to inbreeding depression?
Inbreeding depression = ↓ performance from ↑ homozygosity
Heterosis = ↑ performance from ↑ heterozygosity
Both result from allele combinations, not directly inherited.
What are common purposes of crossbreeding?
Improve production efficiency
Combine desirable traits
Introduce diversity or specific genes
Exploit heterosis
Develop new breeds
What two factors should be considered when evaluating crossbreeding success?
Additive genetic merit of parent breeds
Non-additive advantage (heterosis)
How is heterosis (%) calculated?
Heterosis=
Mid-parentmean-
Observedhybridperformance/Mid-parentmean
×100
Example: If hybrid = 520 lbs, mid-parent = 500 lbs → Heterosis = 4%
In which traits is heterosis typically the greatest?
Traits related to reproduction, survival, and fitness
Between genetically diverse breeds (e.g., Bos indicus × Bos taurus)
What are the types of heterosis?
Individual (direct): Advantage in crossbred animal
Maternal: Advantage from crossbred dam affecting offspring
Paternal: Advantage from crossbred sire, often in fertility
What are some practical benefits of heterosis in livestock?
Crossbred calves: ↑ viability and growth
Crossbred cows: ↑ fertility, weaning weight, longevity → ↑ lifetime production
What biological mechanisms explain heterosis?
Dominance: Masking of recessive alleles
Epistasis: Gene interactions across loci
Heterosis reverses inbreeding depression by increasing heterozygosity
What modern research fields contribute to understanding heterosis?
Transcriptomics
Proteomics
Metabolomics
Epigenomics
Systems biology (e.g., regulation of metabolism via epigenetic changes)
