Quantitative Genetics Flashcards Preview

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Flashcards in Quantitative Genetics Deck (36):
1

Measurable in numeric terms.
-Polygenic and multifactorial

Quantitative traits

2

-Have quantitative traits
-Phenotypes of Q.T. are distributed along a continuum; series of intermediate phenotypes that fall between 2 extremes
ex. Human height, IQ, dispostion, life-span, metabolism

Continuous variation

3

No degrees of severity

Most traits studied so far that have very distinct phenotypes

4

Clearly defined by one or a few genes
-In nature, the majority of traits do not follow this mode of expression

Discrete phenotypes

5

-Controlled by multiple genes and environmental factors
-Each gene is inherited using Mendelian principles
-Modifier genes, differential gene expression, etc. blend together discrete traits

Quantitative Traits

6

Mode of study that shows inheritance of quantitative traits.

Quantitative Genetics

7

Number of copies of these alleles influence the degree of severity of a trait

Contributing alleles (a.k.a. additive alleles)

8

Color of Wheat Kernels Example

-Vary in color from white to dark red
-Alleles A (red) and B (crimson) result in red pigment, while a and b alleles do not produce pigment

9

One gene variation

F2: 1:2:1 incomplete dominance
increasing Left to right Red and and contributing alleles

10

Two gene variation

F2: 1:4:6:4:1
aabb: 2Aabb and 2aaBb: AABB
Increasing red and contributing alleles

11

Three gene variation

F2: 1:6:15:20:15:6:1
increasing red and contributing alleles

12

More gene pairs result in_______.

"Bell shaped curve"
-Environment "blurs" phenotypic classes.

13

Samples and Populations

-Too difficult to collect data from every individual for a large population
-Sample a random subset of the population
-Population: entire group of individuals
-Sample: a representative subset
-Sample should be randomly selected and large enough
-Unbiased sample: define the rules before experiment

14

Summary of continuous phenotype variance for a group or a population
ex. Human birth weight

Distribution

15

Number to individuals in a sample are plotted (according to phenotype) as a histogram.

Distribution for a quantitative trait

16

Curve of distribution

Lots of phenotypic variance makes a broader curve

17

Nature is not:

In opposition to nurture

18

Nature is:

In correspondence with nurture, influencing one another.

19

How much variation in a phenotype is due to genetic variation versus environmental variation?

Ex: Superior strains of wheat in a field.
Strains=genetics
Field=environment
In humans, environment influences genetics and subtle choices which influence phenotype.

20

-Causes variation within each genotypic class
-Causes "blurring" btwn. phenotypic classes in a continuous distribution
-Studied with modern genotyping methods (PCR, etc)

Enviornment affects/quantitative traits

21

Vp=Vg+Ve+Vg*e

Phenotypic Variance for a trait

22

genotypic variance contribution of allelic differences at multiple genes
ex. genetic trends in height

Vg

23

environmental variance contribution from non-genetic sources
ex. impact of nutrition on human height

Ve

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genotype-by-enviornment variance

Vg*e

25

Example: Milk production in dairy cows

-environmental and genetic influences
-How much variation is genetic?
-use this info to see if we should selectively breed the cattle
-We have 4 breeds(<---genotype) of cows
-Collect mild production data from sample of each breed
-Do statistical analysis to determine if any difference is significant.

26

How much of the phenotypic differences are due to genetic factors.

Heritability

27

None of the variation in phenotype between individuals results from genetic differences (all environmental)

0 heritability factor

28

Half of the phenotypic variation is due to genetic differences between individuals and half is due to the environment

0.5 heritability factor

29

All variation is genetically based

1 heritability factor

30

Example: Fruit Fly egg size in relation to temp

Observation: over many generations, fruit fly egg size increases in cold temps
Question: How much of the size difference is due to the environment versus genetic differences (evolution)?

31

Example: Fruit Fly egg size cont...

Vp=Vg+Ve
-Transfer the cold fruit flies to warm (control) temps and mate
-Transfer the control flies to the cold and mate
-Measure egg size of F2 generation (b/c of maternal effect)
-Using stats of egg size measurement, see if there is a difference in the mean egg size of progeny
-The difference between the two is Vg.

32

What about humans?

Monozygotic twins: phenotypic variance due to Ve

33

True or False? Traits shared by members of the same family do not necessarily have high heritability.

True.
-They have similar environments.

34

Individual loci that play a role in quantitative traits.

Quantitative trait loci (QTL)

35

All QTL and how they interact.

Genetic architecture of a trait.

36

Study of QTL

Use molecular tools and statistics to link quantitative phenotypes and QTLs.