Chapter 19

Question 1

Discontinuous variation

Answer 1

variation that produces discrete sharply distinguishable phenotypic categories, allowing for consistent phenotype ratios (3:1 or 9:3:3:1) - in single gene traits

Question 2

Continuous variation

Answer 2

variation distributed across a range of values in an uninterrupted continuum - in polygenic and multifactorial traits

Question 3

Human height is…

Answer 3

a multifactorial trait with continuous variation

Question 4

In addition to genetics, human height is affected by ____________ and ____________ factors

Answer 4

developmental and environmental factors - nutrition, exercise, rest

Question 5

In regard to adult human height, there are more than ____ genetic variants

Answer 5

700

Question 6

Genetic Potential

Answer 6

is transmitted by parents to offspring, which can be attained if the offspring grows and develops under ideal conditions

Question 7

Different genes contribute to polygenic traits differently, Major Genes have ______ influence while Modifier (Minor) Genes have _____ influence

Answer 7

greater, less

Question 8

_______ is a major gene that influences eye color while ______ is a major gene that influences both eye color and skin tone

Answer 8

HERC2, OCA2

Question 9

Additive Genes

Answer 9

when multiple genes make incremental contributions to a phenotypic value - in polygenic traits where no major gene effects are observed

Question 10

The alleles of each ________________ can be assigned their own quantitative values of contribution

Answer 10

additive gene

Question 11

Multiple-gene hypothesis

Answer 11

the hypothesis that alleles of each of the contributing genes obeyed the principles of segregation and independent assortment and had an additive effect in the production of phenotypic variation

Question 12

To test the multiple-gene hypothesis, Nilsson-Ehle used two additive genes (A + B) that both had two alleles A1, A2, B1, and B2. Alleles ___ and ____ add an equal unit of color to the phenotype while ____ and ____ add no color. The more “__________” alleles a genotype has, the darker the color of what kernels and vice versa.

Answer 12

A1 and B1, A2 and B2, number 1

Question 13

The number of phenotypes follows the rule “_______” where ______________

Answer 13

2n+1, n = the number of genes

Question 14

The more additive genes there are that contribute to a phenotype, the ______ phenotypes there are, causing ______ demarcation between categories

Answer 14

more, less

Question 15

In 1916, East used Nicotiana longiflora corolla length to test the multiple-gene hypothesis. He took pure-breeding long and short corolla lines and measured progeny. His two conclusions were…

Answer 15

(1) the intermediate corolla length in progeny results from segregation of alleles of multiple genes
(2) phenotypic expression is also influenced by environmental factors

Question 16

T or F: when there is no gene-environment interaction, F2 phenotypic distribution is discontinuous with a predictable 1:2:1 ratio. With moderate gene-environment interaction, there’s a range of phenotypic values with F2 progeny having some overlap. Finally, substantial gene-environment interaction results in F2 progeny that have significant overlap

Answer 16

True

Question 17

Phenotype = ……

Answer 17

P (phenotype) = G (genotype) + E (environment) + GEI (genotype-environment interactions)

Question 18

GEI (genotype-environment interactions) is estimated …

Answer 18

only when several genotypes are assayed in several defined environments

Question 19

Threshold Trait

Answer 19

a polygenic/multifactorial trait that has continuous distribution but can be divided into distinct categories (like affected or unaffected)

Question 20

Genetic Liability

Answer 20

the idea that certain alleles can push the phenotype toward the affected end of a continuous distribution, each individual’s risk of having the affected phenotype is the result of genotype or in the case of multifactorial phenotypes the genotype and nongenetic influences

Question 21

Threshold of Genetic Liability

Answer 21

the point when an individual will show the affected phenotype - environmental factors can contribute to reaching threshold

Question 22

Variance (s^2)

Answer 22

a measure of the spread of distribution around the mean
s^2 = sum [(x,i - x,bar)^2] / df

Question 23

Phenotypic Variance = ……

Answer 23

VP (phenotypic variance) = VG (genetic variance - genotypic contribution) + VE (environmental variance - environmental contribution)

Question 24

In parental pure-breeding lines, VP = VE since both parental lines are genetically uniform (VG = 0). In F1, VP = ________ and in F2, VP = _________

Answer 24

VP = VE, VP = VE + VG

Question 25

Genetic Variance (VG) has three kinds of allelic effects... | *AID

Answer 25

(1) Additive Variance (VA): added effects of all alleles contributing to the trait (2) Dominance Variance (VD): contributions due to heterozygous individuals not intermediate between the two homozygous states (3) Interactive Variance (VI): epistatic interactions between alleles of genes

Question 26

Heritability

Answer 26

the proportion of phenotypic variation that is due to genetic variation

Question 27

T or F: a high heritability value indicates most of the observed phenotypic variation is due to environmental influences while a low heritability value indicates that most of the observed phenotypic variation is due to genetic variation

Answer 27

False, it's opposite.

Question 28

The two measures of heritability are __________________ and ____________.

Answer 28

Broad-sense heritability, Narrow-sense heritability

Question 29

Regarding the two measures of heritability, what are their respective equations and what do they estimate?

Answer 29

Broad-Sense (H^2 = VG / VP): estimates the proportion of phenotypic variation that is due to total genetic variation Narrow-Sense (h^2 = VA / VP): estimates the proportion of phenotypic variation that is due to additive genetic variation

Question 30

Cave Fish case study: if you know the F1 fish are genetically uniform and that VP(F1) = 0.057cm and VP(F2) = 0.563cm, what is H^2?

Answer 30

H^2 = VG / VP Since F1 is genetically uniform, VP(F1) = VE(F1) = 0.057cm Since VE(F1) = VE(F2), VE(F2) = 0.057cm VP(F2) = VG(F2) + VE(F2) VG(F2) = 0.563cm - 0.057cm = 0.506cm H^2 (F2) = 0.506cm / 0.563cm = 0.899 Conclusion: roughly 90% of phenotypic variation in eye size between these two populations of blind or sighted cave fish is due to genetic variation

Question 31

Since identical twins share all their alleles, VP(mz) = _____ but because fraternal twins share half their alleles, VP(dz) = ____________. This means VG = 2 [VP(dz) - VP(mz)]

Answer 31

VP(mz) = VE VP(dz) = VE + 1/2(VG)

Question 32

The three caveats of Broad Sense Heritability are (1) Stronger ______, (2) Greater _______, and (3) Greater ___________.

Answer 32

(1) Stronger shared maternal effects in identical twins than in fraternal twins (2) Greater similarity of treatment by parents of MZ than DZ twins (3) Greater similarity of interactions between genes and environment in MZ than DZ twins

Question 33

What does a high narrow-sense heritability value correlate to?

Answer 33

A greater degree of response to selection (artificial or natural selection)

Question 34

Four attributes of heritability are central to its meaning, what are they?

Answer 34

(1) Heritability is a measure of the degree to which genetic differences contribute to phenotypic variation of a trait (2) Heritability values are only accurate for the environment and population in which they are measured (3) Heritability for a given trait in a population can change (4) High heritability does not mean a trait is not being influenced by environmental factors at all

Question 35

Quantitative trait loci (QTLs) are genes...

Answer 35

that contribute to phenotypic variation in quantitative traits

Question 36

QTL Mapping is when you..

Answer 36

map QTLs to chromosome regions/linkage groups

Question 37

T or F: a chromosome region likely to contain a QTL is identified by frequent co-occurrence of an SNP with a particular phenotype

Answer 37

True

Question 38

There are two QTL Mapping Strategies: __________ and _________

Answer 38

Genetic Crosses, GWAS (genome-wide association study)

Question 39

Using genetic crosses to map QTLs, these are the four main steps

Answer 39

(1) construct genetic cross between parental strains w/ different phenotypes (2) determine DNA markers that differ between parental strains (3) obtain phenotype and genotype of all progeny (4) identify associations between phenotype and genotype at individual loci

Question 40

Using GWAS to map QTLs, these are the five main steps

Answer 40

(1) select a natural population (2) obtain their whole genome sequences (3) compares "cases" to "controls" to assess their genotypic difference at each sequence variant (4) nucleotide frequencies showing significant differences between "cases" and "controls" are candidate QTLs (5) need to correct for "false discovery rate" (FDR) to reduce false positives

Question 41

Regarding selection differential (S) and response to selection (R), (h^2) = ________. Ms is ________ and M is _________. Ms - M = selection differential (S). The predicted average for the next generation is ______.

Answer 41

h^2 = R/S Ms = mean phenotype selected for mating M = mean phenotype in parental generation M + R = predicted average for next generation