Quantitative Genetics

Question 1

Measurable in numeric terms.

-Polygenic and multifactorial

Answer 1

Quantitative traits

Question 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

Answer 2

Continuous variation

Question 3

No degrees of severity

Answer 3

Most traits studied so far that have very distinct phenotypes

Question 4

Clearly defined by one or a few genes

-In nature, the majority of traits do not follow this mode of expression

Answer 4

Discrete phenotypes

Question 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

Answer 5

Quantitative Traits

Question 6

Mode of study that shows inheritance of quantitative traits.

Answer 6

Quantitative Genetics

Question 7

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

Answer 7

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

Question 8

Color of Wheat Kernels Example

Answer 8

• 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

Question 9

One gene variation

Answer 9

F2: 1:2:1 incomplete dominance

increasing Left to right Red and and contributing alleles

Question 10

Two gene variation

Answer 10

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

Question 11

Three gene variation

Answer 11

F2: 1:6:15:20:15:6:1

increasing red and contributing alleles

Question 12

More gene pairs result in_______.

Answer 12

“Bell shaped curve”

-Environment “blurs” phenotypic classes.

Question 13

Samples and Populations

Answer 13

• 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

Question 14

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

Answer 14

Distribution

Question 15

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

Answer 15

Distribution for a quantitative trait

Question 16

Curve of distribution

Answer 16

Lots of phenotypic variance makes a broader curve

Question 17

Nature is not:

Answer 17

In opposition to nurture

Question 18

Nature is:

Answer 18

In correspondence with nurture, influencing one another.

Question 19

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

Answer 19

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

Question 20

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

Answer 20

Enviornment affects/quantitative traits

Question 21

Vp=Vg+Ve+Vg*e

Answer 21

Phenotypic Variance for a trait

Question 22

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

Answer 22

Vg

Question 23

environmental variance contribution from non-genetic sources

ex. impact of nutrition on human height

Answer 23

Ve

Question 24

genotype-by-enviornment variance

Answer 24

Vg*e

Question 25

Example: Milk production in dairy cows

Answer 25

• 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.

Question 26

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

Answer 26

Heritability

Question 27

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

Answer 27

0 heritability factor

Question 28

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

Answer 28

0.5 heritability factor

Question 29

All variation is genetically based

Answer 29

1 heritability factor

Question 30

Example: Fruit Fly egg size in relation to temp

Answer 30

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)?

Question 31

Example: Fruit Fly egg size cont…

Answer 31

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.

Question 32

What about humans?

Answer 32

Monozygotic twins: phenotypic variance due to Ve

Question 33

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

Answer 33

True.

-They have similar environments.

Question 34

Individual loci that play a role in quantitative traits.

Answer 34

Quantitative trait loci (QTL)

Question 35

All QTL and how they interact.

Answer 35

Genetic architecture of a trait.

Question 36

Study of QTL

Answer 36

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