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Principles of Inheritance > Lectures 21-22 > Flashcards

Lectures 21-22 Flashcards

1
Q

Define Quantitative Genetics:

Examples? (2)

A

Quantitative genetics is the study of the genetics of continuously varying traits

Examples?
–
activity, reproductive rate, disease resistance
Height, weight, shape, colour, metabolic
–
into distinct categories

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2
Q

Why do we use Quantitative genetics?

A

As geneticists, we want to study genotype
but we mainly measure Phenotype.

  • Study genotype through phenotype
    phenotype
    – we identify 2 genotypes because they differ in phenotype.
  • Not always this simple!
  • Most variation between individuals is quantitative or continuously varying
  • Important in agriculture (plant and animal breeding), medicine
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3
Q

What questions can Quantitative Genetics help answer? (3)

A

Some important questions:
1. Is the variation we see influenced at all by genetic variation?

  1. What proportion of the total phenotypic variation is due to genetic variation?
  2. Do many loci, or only a few, vary with respect to the character?
    How do different loci interact to affect the character?
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4
Q

Why ask questions in quantitative genetics?

A

Why ask the questions?

  1. To predict the value of the offspring from various crosses
  2. To know what is going to be passed on to the next generation and predict the effects

It is difficult when phenotype, not one gene, one

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5
Q

What do we know about the phenotype of an individual?
What affects a person’s phenotype? (P = G +E)

A

P = G +E

Performance = Genetics + Environment

Genetics = 1⁄2 sire + 1⁄2 dam set at conception (can’t change!)
Environment =
- Production system
- nutrition
- health
- management

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6
Q

P = G + E good for the individual. How does this change for a population?

A

Vp = Vg +Ve

Genotype and Phenotype

  1. We see the phenotype and try to estimate the genotype
    Vp =Vg + Ve
  2. We need to establish how much of the variation we see is due to the genes present.
  3. Be careful about choosing or deciding things based on what you see - it can be deceptive
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7
Q

what is heritability? what is an alternative definition for it?

A

How much an individual’s superiority (or inferiority) for a particular trait (phenotype) is due to its genetic make-up (genotype) and in turn passed on to its progeny.

Alternative Defintion?
How reliable an individual’s phenotype is for predicting its genetic merit or ability to pass genes onto the next generation

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8
Q

What is heritability in terms of quantitative genetics? (2)

A
  • Is the variation we see (Vp) influenced at all by genes
  • Only genes passed on from one generation to the next.
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9
Q

What is the Partitioning variance?

A

Vp = Vg +Ve
Vg = Va + Vd + Vi
Vp = Va + Vd + Vi + Ve

  1. What is Va?
    Variance due to additive effects
  2. What Vd?
    Variance due to dominance effects
  3. What is Vi?
    Variance due to interaction effects
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10
Q

What is the heritability equation?

A

h^2 = Va/Vp

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11
Q

What are the 2 types of heritability?

A
  1. Narrow Sense heritability
  2. Broad sense heritability.
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12
Q

Explain Narrow sense heritability (3)

A
  1. additive genetic variance that is passed on to the next generation
  2. determines the degree of resemblance between relatives.
  3. The ratio of additive to total variance is heritability h^2
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13
Q

Why are we most interested in Va?

A
  • Only additive effects are passed from one generation to the next
  • Dominance and epistatic deviations are broken down during gamete formation
  • New combinations in siblings
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14
Q

What does the heritability equation estimate?

A

h^2 estimates - a property of the trait, the population and the environment it was estimated from

  1. some reared in more heterogeneous environments
  2. different populations have different genes ad gene frequencies causing different amounts of genetic variation between populations.
  3. the same trait in different environments may act as two traits.

Use information from relatives to calculate.

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15
Q

Response to selection: what to consider for breeding programs?

A

Trying to make genetic improvement
Trying to make a buck
Trying to save species (captive)
Trying to make an improved variety
Trying to make a new breed

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16
Q

What’s the most important thing to consider in a breeding program?

A

Breeding objectives - where to go.

17
Q

What’s the second most important thing to consider in a breeding program?

A

Selection criteria - how to get there?

18
Q

Do your breeding objectives and selection criteria have to be the same?

A

NO
(Objective trait may be expensive or difficult to measure)

19
Q

What might influence your breeding objectives? (4)

A
  1. Heritability
  2. Economic value
  3. Preference
  4. Conservation
20
Q

What might influence your selection criteria? (4)

A
  1. Heritability
  2. Genetic correlations
  3. Ease of measurement
  4. Cost of measurement
21
Q

Response to selection: how to calculate?

A

Use selection to change the mean of a particular trait in a population.

R = h^2S

R = Response to selection
S = Selection differential

22
Q

Males vs Females Response to Selection Formulas.

A
  • Often the selection differential will differ between males and females.

S = (Sm + Sf) / 2

R = ( (Sm+Sf) /2) x h^2

23
Q

Explain Response to Selection: Selection Intensity (What is it? What parts? What can it predict?)

A

Selection intensity
- standardised selection differential (i)

We can also predict the selection (S) is provided that the phenotypic values of the population
* are normally distributed
* and selection is by truncation.

We can do this if we know
– the proportion of the animals that will be or selected for breeding (p)
– and assuming normality in our population

Express S in standard deviation units, p
We call it selection intensity.

24
Q

Response to Selection: Selection intensity calculation:

A

i = S/theta(p)

S = i(theta(p))
= the number of standard deviation

i = the number of standard deviation units (p’s) that selected parents are superior to the mean of the population.

25
Q

Response to selection equations: 3

A
  1. R =h^2S = Ih^2 *(theta(p))
  2. R(gen) = (( i(m) +i(f) ) / 2) * h^2*( theta(p))
  3. Ryr = (( i(m) + i(f))/ (L(m) + L(f)) h^2 (theta p)
    **L = generation interval.
26
Q

Quantitative Genetics Medical Usages?

A
  • Mapping, discovery, and function of disease genes affecting skin and craniofacial development and autoimmunity
  • Genetics of colon cancer
  • Genetics of eye disorders
  • Genetics of craniofacial and cardiovascular development
  • Population and quantitative genetics with an emphasis on autoimmune diseases

Genome analysis and Quantitative Trait Loci detection

27
Q

Summary of lectures (2)

A

Genes not environment are passed on from one generation to the next

An idea about how we make genetic improvements by selection based on genetic differences

28
Q

Key concepts (5)

A
  1. Variation in most characters is continuous
    * Mendelian analysis is difficult to apply so use statistical analysis
    * Determine the extent environment and genetics contribute to what we see
    * Genetic variation can be a result of segregation at a single locus or at numerous interacting loci
    * Estimates of genetic and environmental variation specific to the population and environments
    -

Principles of Inheritance (23 decks)

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