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AN SC 384 > 7: Breeding Value and Genotypic Value > Flashcards

7: Breeding Value and Genotypic Value Flashcards

1
Q

What is genetics

A

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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2
Q

Frequency of diff alleles change due to…

A

migration, selection and genetic drift

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3
Q

Major source of variation between populations

A

Difference in allele freq

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4
Q

When can allele freqs be used to predict results of mating

A

Mainly for single locus traits

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5
Q

What are polygenic traits

A

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

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6
Q

What is quantitative genetics

A

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

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7
Q

In polygenic traits, phenotype does not tell us about…

A

the entire underlying genotype

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8
Q

Quantitative genetics focuses on…

A

relationship between parents and offspring (connection between animals)

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9
Q

What is measured in quantitative genetics? What is determined?

A

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

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10
Q

Why do quantitative traits show a normal distribution in the population

A
  • underlying genetic distribution (genetic variation)
  • underlying environmental distribution (environmental variation)
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11
Q

Most economically important traits are..

A

polygenic

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12
Q

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

A

When more genes affect that trait

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13
Q

Equation for number of phenotypic classes

A

(n gene pairs * 2) +1

+1 for the het

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14
Q

What is the infinitesimal model for polygenic traits

A

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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15
Q

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

Example of post-weaning and pre-maturity traits

A

Animals own genetics + maternal effects

Animals own genetics + nutritional and current environmental influence

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16
Q

Example of post-maturity and reproductive traits

Example of meat quality and carcass traits

A

Strong influences of non-additive genetic effects and environments

Pre-slaughter stresses and post-mortem conditions

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17
Q

Examples of polygenic traits in beef? Dairy?

A

Calving interval (days), weaning weight

Days open, milk yield

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18
Q

What is unknown when it comes to polygenic traits

A

Alleles or even loci affecting the trait

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19
Q

What is the mean, variance and standard deviation

A

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**

20
Q

Parameters to measure qualitative vs quantitative traits

A

quali: p and q

quanti: mean, variance, SD

slide 18 for full comparison

21
Q

What are the main requirements for genetic improvement

A

Phenotypic variability and heritability

22
Q

What is the breeders equation

A

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

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

23
Q

What part of the breeders equation has the largest effect

A

heritability

24
Q

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

A

P = G + E

phenotypic value = genotypic value + environmental deviation

25
Q

Individual performance is based on…

A

genes and environmental effect

26
Q

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

A

PV = individual performance record

u = average phenotypic value for all animals in pop

these are directly measurable

27
Q

What is genotypic value? Environmental effect?

A

GV = effect of individuals genes on its performance (singly or combination)

EV = all nongenetic factor influencing individual’s performance (environmental deviation)

28
Q

When looking at a graph, phenotypic value is…

A

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

29
Q

Three rules of genetic model for quantitative traits

A
  1. expressed as deviation from population mean
  2. considered independent
  3. average G = average E = 0
30
Q

How are G and E independent?

A

Changing genes at birth does not affect the environment, changing environment does not change genes

But they do interact!

31
Q

We can split genotypic value into three separate components…

A

A = additive genetic effect or independent gene effect

non-additive effects:
D = dominance effect
I = epistasis effect

32
Q

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

A

A is transmitted to offspring

D and I are not because they are due to gene combination effect

33
Q

Because A is transmittable, it is considered…

A

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

34
Q

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

A

P -= u + BV + GCV + E

35
Q

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

A

Dominance (complete, partial, no, over)

Epistasis

36
Q

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

A

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

37
Q

Slides 29, 30

A

Look

38
Q

Why is GCV for the next generation not predictable?

A

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

39
Q

Breeding value is the sum of…

A

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

40
Q

Genotypic value vs breeding value

A

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)

41
Q

Gene combination value is…

A

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

42
Q

The base for phenotypic resemblance between relatives is…

A

breeding value

43
Q

Genotype and environment are independent, but…

A

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

44
Q

Classic example of environment and genotype interacting

A

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

45
Q

To test interaction between genotype and environment you must have…

A

at least two genotypes and at least two environments

46
Q

What traits are most susceptible to G x E interaction

A

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

AN SC 384 (22 decks)

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