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Evolution and Population Genetics > Lecture 4 - Quantitative variation 2 > Flashcards

Lecture 4 - Quantitative variation 2 Flashcards

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1
Q

How does the number of loci affect the distribution of a quantitative phenotype?

A

More loci - more continuous the range of phenotypes

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2
Q

What is phenotypic variatiance?

A

How much of the phenotypic variation is explained by the genotype and how much by the environemnt
-Vp

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3
Q

What is the symbol for phenotypic variance?

A

Vp

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4
Q

What is phenotypic variation due to?

A
  • Genetics
  • Environment
  • Interaction between genes and the environment (different genes may react differently to different environments)
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5
Q

What two exmaples demonstrate phenotypic variation in quantitative traits?

A
  • Corolla length in longflower tobacco (genetics)

- Yarrow height, depnding on location (environment)

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6
Q

How do Yarrow show phenotypic variation?

A

Vary in height depending on their location
Clausen experiment
Measured heights at
-Stanford (30m above sea level) - tallest but most variable
-Mather (1400m above sea level) - middle height
-Timberline (3050m above sea level) - smallest

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7
Q

How can we disentangle genetic and environmental effects?

A
  • transplant experiments
  • common garden experiments
  • twin studies
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8
Q

Describe the components of phenotypic variation (Vp) when plants are grown in two trays: one in a Normal uniform nutrient solution and one that is deficient (in terms of VG and VE)

A
  • within each tray, phenotypic variation is mostly to do with genetic variation (VG)
  • between trays it is mostly to do with environmental variation (nutrient availability) - (VE)

Therefore VP = VG + VE

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9
Q

What is the symbol for genetic variance?

A

VG

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10
Q

What is the symbol for environmental variance?

A

VE

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11
Q

What is the equation for VP (in terms of VG and VE)?

A

VP = VG + VE + V(GXE)

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12
Q

How does a shared environment affect phenotypes?

A

A shared environment increased phenotypic resemblance e.g. units of pigment shows a more continuous range of phenotypes (typical bell curve) when in a shared environment

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13
Q

What components affect genetic variation?

A 
VA = additive genetic variance (effects of allele substitutions)
VD = dominance genetic variance (effects of allelic interactions at the same locus)
VI = epistasis/interaction genetic variance (effect of interactions between different loci)
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14
Q

What is dominance genetic variance?

A

VD
-the effects of alleleic interactions at the same locus

e.g. A1A1 - tall plant
A1A2 - tall plant
A2A2 - small plant

Tall is dominant

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15
Q

What is additive genetic variance?

A

VA

  • additive effects of allele substitutions
  • co dominance (midway phenotype)

e.g. A1A1 - tall plant
A1A2 - med height plant
A2A2 - small plant

Add up the effects of both phenotypes

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16
Q

What is epistasis/interaction genetic variance?

A

VI

  • effects of interactions between different loci
  • e.g. epistasis

e.g. A1A1B1B1 - tall plant
A2A2B2B2 - tall plant
A1A1B2B2, A2A2B1B1 - small plant
interactions

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17
Q

What is VG?

A

The components of genetic variation

18
Q

What is the formula for VG (in terms of VA, VD and VI)?

A

VG = VA + VD + VI

19
Q

What are the inheritance features of VA, VD and Vi?

A

VA - simple pattern of inheritance compared to VD and VI, caused by average of the phenotypic effects
VD and VI caused by phenotypic effects of genotypes

20
Q

How are the inheritance effects of VD illustrated?

A

Box plot thing whatever they’re called

Typical mendelian first law of segregation box

21
Q

How is the inheritance effects of VI illustrated?

A

Massive box plot thing
e.g. B = black, b = brown, E = pigment there, e = pigment not (Dog colour)
4 X 4 = 16 different traits

22
Q

How did the Clausen (Timberland, Mather, Standford) experiment show that the interaction between genes and the environment also affects phenotypic variation?

A

At high altitude (timerland) - some plants died(San gregario), whilst others didn’t (big horn lake)
At intermediate altitude (Mather) - some plants grew tall (San gregario) whilst others were small (Big horn lake)
At low altitude - the phenotypes changed again, San gregario v tall, Big horn lake not the leafiness it was at intermediate, more like a small version of the flowring plant it was at high altitude

Showed phenotypuc plasticity

23
Q

What is phenotypic plasticity?

A

When a genotype expresses different phenotypes depending on the environment

24
Q

What are genotype-envirpnemtn interactions?

A

When a genotype expresses different phenotypes depending on the environemtn, and different genotypes have different kinds of phenotypic plasticity

25
Q

What are the 5 types of GenotypeXEnvironment interactions?

A
  • VG only
  • VE only
  • VG and VE
  • V(EXG) - phenotypic plasticity
  • V(EXG) - phenotypic plasticity - genoptype-environment interaction
26
Q

How is correlation between twins different for monozygotic and dizygotic twins?

A

Higher phenotypic correlation with monozygotic twins

27
Q

What is heritability?

A

-the proportion of phenotypic variation in a population that is attributable to genetic variation among individuals within a population

28
Q

What are some common misconceptions about heritability?

A
  • does NOT measure whether a trait has a genetic basis or not
  • a heritability when h2 = 0 does not mean that trait has no genetic basis
29
Q

What is broad sense heritability?

A
  • the proportion of phenotypic variation that is due to genetic variation (including addivitive variation, dominance and epistasis)
  • relatively easy to measure, as long as there is no association between environment and genotype
30
Q

What is the symbol and formula for broad sense heratibility?

A

H2

=VG/VP
=(VA+VD+VI)/(VP)

31
Q

What is narrow sense heritability?

A

-The proportion of phenotypic variation that is due to additive variation
(mostly additive genetic variation VA contributes to parent-offsping resemblance)
-harder to measure

32
Q

What type of variation mostly contributes to parent-offspring resemblance?

A

Additive genetic variation

33
Q

What is the symbol and formula for narrow sense heritability?

A

h2

h2=VA/VP

34
Q

How do heritability values vary and why?

A

Heritability values are a proportion

-vary from 0 to 1

35
Q

How can we estimate narrow sense heritabilty in natural populations?

A

Resemblance between relatives

  • parent offspring regression
  • Sibling analysis
36
Q

What is Midparent?

A

-the average phenotypic value of the mother and father

37
Q

In a graph of Mid-parent offspring regression, what does the narrow sense heritability equal?

A

The slope of the regression line

h2 = b

38
Q

How can narrow sense heritability in one parent offspring regression be calculated?

A

-the narrow sense heritability is twice the slope of regression
h2 = 2b
-based on the fact that one parent is contributing less to the offspring phenotype than both together

39
Q

What are the features of mother/father one parent offspring regression?

A

-differences in heritability between mothers and fathers ffrom one parent-offsping regression = Maternal effects

40
Q

What are maternal effects?

A
  • offspring often resemble their mother more than their father
  • due to a shared environment/experience e.g. in womb
  • therefore father offspring regressions better indicator of narrow sense heritability
41
Q

Why are father offspring regressions better indicators of narrow sense heritability?

A
  • offspring often resemble their mother more than their father
  • due to a shared environment/experience e.g. in womb

Evolution and Population Genetics (13 decks)

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