Genetics Chapter 20

Phenotypes result from both gene action and environmental influences (polygenic traits)

Multifactorial

What is used to calculate Narrow-sense heritability?

Additive variance

variance due to additive action of alleles at quantitative trait loci

Additive variance (Va)

Wild and domesticated peaches are an example of:

Artificial selection

1. continuous variation 2. polygenic inheritance 3. additive/nonadditive allele 4. phenotypic variation

Four points of Multiple gene hypothesis

Additive alleles contribute to a single quantitative trait to produce substantial phenotypic variation

Fourth point of Multiple gene hypothesis

proportion of total phenotypic variation in population due to genetic factors

Heritability

proportion of phenotypic variation attributed to genetic variation within a certain population in a particular environment

Heritability Estimate

broken into genotypic variance (Vg) and environmental variance (Ve)

phenotypic variance (Vp)

How many gametes are involved in the formation of monozygotic twins?

2 (identical twins)

additive, dominance, interactive

3 subsets of genotypic variance:

Calculate the standard deviation of the following values: 8, 12, 8 and 4.

3.26

Eye color in humans is a polygenic trait influenced by 16 genes. How many phenotypic classes of eye color would you expect?

33

How many gametes are involved in the formation of dizygotic twins?

4 (fraternal twins)

Measures contribution of genotypic variance to total phenotypic variance, assumes that genotype-by-environment variance is negligible

Broad-sense Heritability (H^2)

H = Vg/Vp

Broad-sense Heritability formula (H=H^2)

both or neither twin expresses trait

Concordant

Indicates if two traits increase or decrease together or separate

Correlation coefficient (r)

Measures how much variation is common to two quantitative traits

Covariance

derived from two separate fertilization events, fraternal twins

Dizygotic

one twin expresses trait and other doesn't

Discordant

Deviation from additive components that results when phenotypic expression in heterozygotes is not precise

Dominance variance (Vd)

explain variation in expression levels of mRNAs, identify genes that cause complex diseases

Expression quantitative trait loci (eQTL)

Phenotypic traits show continuous variation and can be quantified

First point of Multiple gene hypothesis

look at scanning markers in genomes of many individuals to find genetic variations associated with a particular trait or disease

Genome-wide association studies (GWAS)

genetically determines, phenotype, genotype

Heritability does not indication how much of the trait is ______________________ or the extent to which an individuals _____________________ is due to ___________________

genetic factors

High heritability is attributed to

Deviation from additive components that occurs when two or more loci behave epistatically

Interactive variance (V

Which of the following describes an expression quantitative trait loci (eQTL)?

Lactose tolerance level is determined by lactase enzyme alleles with different mutations in the promoter that influence the gene's mRNA levels

continuous variation can be measured in quantitative terms

Quantitative inheritance

Which of the following is an example of G x E interaction?

Lobsters with allele A grow larger than lobsters with allele a in cold water environments. In warm tropical waters lobsters with allele a grow larger.

environmental factors

Low heritability is attributed to

You find the heritability of height of in a population water oak trees in upstate South Carolina to be 0.67. Your colleague finds the heritability of height of in a population water oak trees in south Alabama to be 0.44. How is this possible?

Measured heritability depends on environmental variation present in population being studied

derived from single zygote, identical twins (gene-expression patterns can vary with age bc they dont have identical genomes)

Monozygotic

The why is heritability of having two eyes very low?

Most of the variation in eye number is due to accidents and injuries

You are studying the Virginia opossum, Didelphis virginiana. You find 11 genes that influence the weight of newborn joeys, and that the mother's diet also influences birth weight. What term best describes this trait?

Multifactorial

Proportion of phenotypic variance due to additive genotypic variance alone

Narrow-sense Heritability (h^2)

h=Va/Vp

Narrow-sense Heritability formula (h=h^2)

Which of the following is NOT a major point of the multiple-gene hypothesis?

Phenotypic traits show discontinuous variation and can be cannot be quantified, only qualified

genes contributing to polygenic trait

Polygenes (n)

varying phenotypes result from input of genes at more than one loci

Polygenic

A locus that contains a gene or genes contributing to quantitative trait

Quantitative Trait Loci (QTLs)

1.Two or more loci show an additive effect on the expression of phenotype (polygenic inheritance)

Second point of Multiple gene hypothesis

What is the difference between standard deviation and standard error?

Standard error takes sample size into account

Each gene loci is occupied by either additive or nonadditive allele

Third point of Multiple gene hypothesis

Which of these traits are monozygotic twins most likely to be discordant for?

Uterine cancer

Height in a species of plant is controlled by 4 genes with additive alleles. Which of the following is a genotype you would expect for a plant of average height?

aaBBCcDd

average of set of measurements

define mean

square root of variance, defines boundary where 95% of values are found

define standard deviation

describes errors between means determined for multiple samples of the same group, is always smaller than SD

define standard error of the mean

Average squared distance of all measurements from mean

define variance

1/(4^n)

formula for ratio of F2 individuals expressing their extreme phenotype =

traits increase and decrease separately

negative correlation coefficient (r) means

traits increase and decrease together

positive correlation coefficient (r) means

You are studying corn and find that higher stalk height is correlated with larger cob size. Which of the following r values would be expected for this relationship?

r = +0.78

spread of data around mean

variance provides information about _________________________