Lecture 12: Quantitive Genetics Flashcards Preview

APS125 Genes in Populations > Lecture 12: Quantitive Genetics > Flashcards

Flashcards in Lecture 12: Quantitive Genetics Deck (37):
1

Name 3 types of phenotypic variation

discontinuous
continuous (quantitive)
Threshold

2

Discontinuous variation:

-Discrete classes of phenotype
- NO intermediates
- Follows Mendelian ratios
- Simple genetic basis, limited effect of the environment
e.g. red/white pea flowers
widow peak, dimple and blood groups

3

Continous variation:

Also known as: quantitive, complex or multifactorial.
-phenotypes do not fall into classes
-offspring of intermediate phenotype
-CANNOT observe Mendelian ratios
-Complex genetic basis plus effect of the environment
-E.g. Height, blood pressure, Beak size

4

Graph used to show continuous variation data:

'Normal' (Gaussian) Graph. Upside bell shape.

5

What does the graph used for continuous variation data show us?

Peak = MEAN.
68% oh width = standard deviation (measure of spread)

6

Variance =

sd^2

7

Threshold variation:

-appears like a discontinuous trait BUT is caused by a continuous distribution.
-distribution caused liability
-phenotype depends on critical threshold
-no simple segregation in families

8

E.g of threshold variation:

Type 2 diabetes.
As number of predisposing alleles in genotype increase past threshold zone then you're considered to have DIABETES. Measure of liability.

9

How do genes cause continuous variation?

Think of coin tossing.
1 toss = 1H 1T
2 toss = 2H 1H1T 2T
3 toss = Even more inbetween values (More possible ways for middle values to be made) =NORMAL GRAPH SHAPE.
same thing if many genes contribute to variation in a trait

10

Lots of genes contributing to one trait that are close together ==

Quantitive Trait Locus (QTL)

11

Complications to continuous variation?

-Genes vary in the size of their effect
-Allele frequencies vary
-Some alleles are dominant/ co-dominant
AND ENVIRONMENT has a huge effect

12

You're more similar to your siblings than a stranger? WHY?

you inherited some of the same alleles from your parents (NATURE) you grew up in the same environment (NURTURE)

13

Monozygotic twins:

IDENTICAL

14

Dizygotic twins:

NOT IDENTICAL

15

do genes or environment contribute to quantitive traits?

BOTH

16

The total variation within a population for a phenotype is measured by the..

PHENOTYPIC VARIANCE (Vp)

17

Phenotypic variance 2 components:

-Genetic variance (Vg)
-environmental variance (Ve)

18

Genetic variance (Vg)...

Variation due to differences in genotype

19

Environmental variance (Ve)...

Variation due to environmental effects

20

If genetic & environmental effects are independent you can write...

Vp = Vg + Ve

21

Heritability =

H^2 = Vg/Vp

22

H^2 is called the..

'broad sense heritability' of the trait

23

Broad sense heritability...

'the proportion of the phenotypic variation in a population that is due to genetic differences among individuals'

24

Broad sense heritability is often expressed as a

%

25

H^2 = Vg/Vp =

Vg/(Vg+Ve)

26

What happens to heritability when we DECREASE genetic variance?

Heritability decreases

27

What happens to heritability when we INCREASE genetic variance?

Heritability increases

28

Do estimates of heritability for a particular trait change among populations?

Populations living in different environments can show different degrees of heritability for a particular trait.

29

Heritability estimates for a trait are...

relative to the genetic & environmental factors in the population

30

The effect of inbred individuals on heritability..??

= 0 heritability after long time.
As Vg (genetic variance) = 0 over time

31

What does 0 heritability mean?

A zero heritability DOES NOT mean that a trait is not genetically determined.

32

Why is heritability an excellent predictor for short-term but NOT long-term response

Allele frequencies change over time due to selection and/or genetic drift. This change affects Vg & in turn, heritability.

33

Genotype-environment interaction is known as...

Nature vs nurture

34

Genotype-environment interaction is represented by th equation:

Vp = Vg + Ve + VgXe

35

One way to handle GxE is to consider....
And whats it called

the response to environmental variation as the quantitive trait
called 'norm of reaction'

36

The norm of reaction:

a curve that relates, for a given genotype, the contribution of environmental variation to observed phenotypic variation.

37

Heritability is specific to...

the population and environment in which it is measured.