7: Breeding Value and Genotypic Value Flashcards by Megan Ganley

What is genetics

Study of heredity of all kind of traits
Evaluates how differences btw individuals are transmitted from one gen to the next

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Frequency of diff alleles change due to…

migration, selection and genetic drift

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Major source of variation between populations

Difference in allele freq

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When can allele freqs be used to predict results of mating

Mainly for single locus traits

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What are polygenic traits

Traits that are influenced by many genes and environmental factors
Numerous possible phenotypes
Continuous or categorical variation

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What is quantitative genetics

The analysis of traits whose variation is determined simultaneously by many genes and environmental factors

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In polygenic traits, phenotype does not tell us about…

the entire underlying genotype

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Quantitative genetics focuses on…

relationship between parents and offspring (connection between animals)

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What is measured in quantitative genetics? What is determined?

Performance (phenotype) of individuals of known genetic relationship (pedigree) are measured
Genetic and environmental sources of variation are determined statistically

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Why do quantitative traits show a normal distribution in the population

underlying genetic distribution (genetic variation)
underlying environmental distribution (environmental variation)

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Most economically important traits are..

polygenic

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When does it become difficult to observe and separate the effects of individual genes

When more genes affect that trait

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Equation for number of phenotypic classes

(n gene pairs * 2) +1

+1 for the het

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What is the infinitesimal model for polygenic traits

Increasing the # of genes affecting the trait will increase the # of phenotypic classes and lead to a normal distribution

Slide 14**

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Example of pre- and post-birth, pre-weaning traits

Example of post-weaning and pre-maturity traits

Animals own genetics + maternal effects

Animals own genetics + nutritional and current environmental influence

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Example of post-maturity and reproductive traits

Example of meat quality and carcass traits

Strong influences of non-additive genetic effects and environments

Pre-slaughter stresses and post-mortem conditions

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Examples of polygenic traits in beef? Dairy?

Calving interval (days), weaning weight

Days open, milk yield

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What is unknown when it comes to polygenic traits

Alleles or even loci affecting the trait

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What is the mean, variance and standard deviation

Mean: sum of all measurements divided by # of measurements

Variance: average squared deviation of the observations from the mean

SD: square root of variance

Slide 17 to see equations**

Parameters to measure qualitative vs quantitative traits

quali: p and q

quanti: mean, variance, SD

slide 18 for full comparison

What are the main requirements for genetic improvement

Phenotypic variability and heritability

What is the breeders equation

deltaG = h^2 * sd * a * (i/t)

genetic progress = heritability * variation * accuracy * intensity of selection

What part of the breeders equation has the largest effect

heritability

How do we separate genetic influence from environmental influence for polygenic traits?

P = G + E

phenotypic value = genotypic value + environmental deviation

Individual performance is based on...

genes and environmental effect

What is phenotypic value? population mean? How do you measure

PV = individual performance record u = average phenotypic value for all animals in pop these are directly measurable

What is genotypic value? Environmental effect?

GV = effect of individuals genes on its performance (singly or combination) EV = all nongenetic factor influencing individual's performance (environmental deviation)

When looking at a graph, phenotypic value is...

compared to the average of the population P - u e.g. if the mean is 500lb weaning weight, then a cow weighing 550lb will be at +50 on the graph

Three rules of genetic model for quantitative traits

1. expressed as deviation from population mean 2. considered independent 3. average G = average E = 0

How are G and E independent?

Changing genes at birth does not affect the environment, changing environment does not change genes But they do interact!

We can split genotypic value into three separate components...

A = additive genetic effect or independent gene effect non-additive effects: D = dominance effect I = epistasis effect

Which of A, D and I are transmitted to offspring? Why?

A is transmitted to offspring D and I are not because they are due to gene combination effect

Because A is transmittable, it is considered...

as a Breeding Value (BV) i.e. value as a genetic parent

The complete equation of the genetic model for quantitative traits is...

P -= u + BV + GCV + E

Interactions between alleles at one locus is... Interaction between genes at different loci is...

Dominance (complete, partial, no, over) Epistasis

The best animals to chose as parents for the next gen are...

The ones with the highest breeding value (BV) = best sets of genes

Slides 29, 30

Look

Why is GCV for the next generation not predictable?

Combination of genes will be lost as parents only transmit half of their gene alleles to their offspring

Breeding value is the sum of...

the independent effect of all that animal's genes on a trait

Genotypic value vs breeding value

GV = value of genes to SELF (effect of individuals genes on its own phenotypic performance) BV = value of genes to PROGENY (that part of the genotypic value that can be transmitted from parent to offspring)

Gene combination value is...

the part of the genotypic value that is not transmitted from parents to offspring

The base for phenotypic resemblance between relatives is...

breeding value

Genotype and environment are independent, but...

they interact Genotypes respond differently across a range of environments Diff in performance btw two (or more) genotypes changes from env to env

Classic example of environment and genotype interacting

Animals that are genetically adapted to temperate locations versus animals genetically adapted to tropical areas Performance of animals used to temperate will suffer in tropical

To test interaction between genotype and environment you must have...

at least two genotypes and at least two environments

What traits are most susceptible to G x E interaction

Traits that are less influenced by the animal genotype (low heritability) like fertility and survivability