Quantitative Genetics and Complex Traits

Question 1

Identify

Traits wherein varying phenotypes are a result from the input of genes at more than one loci

Answer 1

Polygenic traits

Question 2

Identify

Quantitative traits whose phenotypes result from both gene action and environmental influences

Answer 2

Multifactorial (or Complex) Traits

Question 3

Identify

Another term for Multifactorial Traits

Answer 3

Complex Traits

Question 4

Identify

Three categories of traits found to have complex inheritance

Answer 4

1. Continuous/quantitative traits
2. Meristic traits
3. Threshold traits

Question 5

Identify

A hypothesis that states that many genes, each individually exhibiting Mendelian behavior, contribute to the phenotype in a quantitative way

From Klug, W. S., Cummings, M. R., Spencer, C. A., Palladino, M. A., & Killian, D. (2020). Essentials of genetics (10th ed.). Pearson.

Answer 5

Multiple-gene hypothesis

Question 6

True or False

Additive alleles contribute a constant amount to the phenotype

Answer 6

True

Question 7

True or False

Each additive allele’s contribution to the phenotype is equal

Answer 7

True

Question 8

Multiple Choice

What is the ratio of F2 individuals expressing either extreme (P1) phenotype?
1. 1/4^n
2. 1/8^n
3. 1/6^n
4. 1/3^n

From Klug, W. S., Cummings, M. R., Spencer, C. A., Palladino, M. A., & Killian, D. (2020). Essentials of genetics (10th ed.). Pearson.

Answer 8

A. 1/4^n

Usually these are the F2 offsprings that express the parental phenotype.

Question 9

Identify the equation

How do you determine the number of gene pairs/polygenes (n) contributing to a trait?

gene pairs can be used synonymously to “polygenes”

From Klug, W. S., Cummings, M. R., Spencer, C. A., Palladino, M. A., & Killian, D. (2020). Essentials of genetics (10th ed.). Pearson.

Answer 9

n = log (fraction of F2 as extreme as one parent) / log (1/4)

Question 10

Calculate

Solve for n:
* In a group of 72 F2 offsprings, 1 exhibits aabb and 1 exhibits AABB genotypes.

Note: Fraction of F2 as extreme as one/either parent

From Klug, W. S., Cummings, M. R., Spencer, C. A., Palladino, M. A., & Killian, D. (2020). Essentials of genetics (10th ed.). Pearson.

Answer 10

• Remember equation n = log (fraction of F2 as extreme as one parent) / log (1/4)
• Fraction of F2 as extreme as one/either parent is 1/72
• n = [log (1/72)] / [log (1/4)]
• n = 3.085 ~ 3
• Thus, there are 3 gene pairs (or polygenes) that control the trait

Question 11

Identify the Equation

Number of distinct phenotypic categories observed

Not in the powerpoints.

From Klug, W. S., Cummings, M. R., Spencer, C. A., Palladino, M. A., & Killian, D. (2020). Essentials of genetics (10th ed.). Pearson.

Answer 11

(2n+1)
* For example if there are 2 polygenes involved (n=2), then there are (2(2) +1) = 5 phenotypic categories
* Each phenotype is the result of 4, 3, 2, 1, or 0 alleles

Question 12

True or False

Data seen in Polygenic traits form a normal distribution (bell curve)

Answer 12

True

Question 13

Identify

(1) and (2) of various kinds will cause the distribution curve to appear symmetrical

Answer 13

1. Non-additivity
2. Interactions

Question 14

Identify

Aside from non-additivity and interactions, what else is a modification of additive effects?

Answer 14

Dominance between alleles

Question 15

True or false

In discontinuous traits, those individuals below the “threshold” number of contributory genes will have one phenotype and those at threshold value or above it will have another phenotype

Answer 15

True

Question 16

Identify

Proportion of total phenotypic variation in a population that is due to genetic factors

Answer 16

Heritability

Question 17

Identify the following

Phenotypic variance (Vp) is partitioned to:
1. ____
2. ____
3. ____

From Klug, W. S., Cummings, M. R., Spencer, C. A., Palladino, M. A., & Killian, D. (2020). Essentials of genetics (10th ed.). Pearson.

Answer 17

1. Genotypic variance (VG)
2. Environmental variance (VE)
3. Genotype-by-Environment variance (Vgxe)

Question 18

True or False

Variation between different inbred strains in a constant environment is due predominantly to genetic factors

Answer 18

True

Question 19

Identify

Measures the contribution of Genotypic variance (VG) to the total phenotypic variance (VP)

Answer 19

Broad-Sense Heritability (H^2)

Question 20

Identify

H^2 is equal to

Answer 20

H^2 = VG/VP

Question 21

Multiple Choice

Geneticists discover that, for a certain trait, its Broad-Sense Heritability is 0.02. What can be said about its H^2?
1. Genotypic variance plays a huge role in the total phenotypic variance.
2. Both Environmental and Genotypic variance play a huge role in the total phenotypic variance
3. Environmental variance plays a huge role in the total phenotypic variance
4. There is no variance at all

Answer 21

Environmental variance plays a huge role in the total phenotypic variance, if H^2 is low
* If H^2 is low, genotypic variance (VG) plays a minor part in total phenotypic variance, and Environmental variance (VE) contributes more to such.

Question 22

True or False

Broad-sense Heritability includes all types of genetic variation in the population

Answer 22

True

Question 23

Identify

All genetic variations in the population

Answer 23

• VD = Dominance-based (Mendelian)
• VI = Epistatic
• VA = Additive

Question 24

True or False

Broad-Sense Heritability is used as a genetic basis in breeding programs

Answer 24

False; it is Narrow-Sense Heritability that is used in Breeding Programs

Question 25

# Identify Measures the proportion of phenotypic variance due to additive genotypic variance alone

Answer 25

Narrow-Sense Heritability (h^2)

Question 26

# True or False VG = VE + VI + VP

Answer 26

**False**; VG = VI + VA + VD * Vg = genotypic variance * Vi = epistatic genotypic variance * Va = additive genotypic variance * Vd = dominant genotypic variance

Question 27

# True or False All phenotypic variance in F1 generation is due to genotypic variance

Answer 27

**False**; It is due to Environmental Variance

Question 28

# Identify Variance in the F2 generation is equal to

Answer 28

Vf2 = VG + VE

Question 29

# Identify equation Genetic variance is equal to:

Answer 29

1. Phenotypic variance of F2 generation minus Phenotypic Variance of F1 generation (**Vf2 - Vf1**) 2. **[a^2(N)]/2** 3. **D^2/8N** wherein a = contribution of each additive allele wherein N = number of gene pairs involved in the quantitative trait wherein D = numerical difference between two (2) parental means

Question 30

# Identify equation Contribution of each additive allele (**a**) is equal to

Answer 30

a = D/2N

Question 31

# Identify equation Numerical difference between the two parental means | Hint: derive equations

Answer 31

D = (a)(2)(N)

Question 32

# Identify All assumptions in variance method

Answer 32

* All generations are reared in the same environment * The alleles of each gene are additive * Genes contribute equally to the trait * Genes are unlinked * Original parental strains are homozygous for the alternative alleles * No dominance * No interaction

Question 33

# Identify the equations Narrow-Sense heritability is equal to:

Answer 33

1. Va/Vp 2. Va/Ve+Vd+Va 2. (M2-M)/(M1-M) 3. Correlation Coefficient in monozygotic (MZ) twins | Equation 2- epistatic variance is negligible

Question 34

# True or False In terms of accuracy, h^2 > H^2

Answer 34

True; thus, h^2 is preferred by breeders.

Question 35

# Identify Process of Choosing specific individuals with preferred phenotypes from an initially heterogenous population

Answer 35

**Artificial Selection**

Question 36

# True or False Narrow-Sense Heritability (h^2) **cannot be used** to predict the impact of artifical selection

Answer 36

False; it can be used

Question 37

# True or False The higher the h^2, **the more likely** there will be change in phenotypic range for the trait in the next generation after artificial selection

Answer 37

True

Question 38

# Identify h^2, **in terms of mean scores in the population**, is equal to

Answer 38

h^2 = (M'-M)/(M*-M) 1. M - mean phenotype of the entire population in the parental (P1) generation 2. M' - mean phenotype among those individuals selected as parents 3. M* - mean phenotype among the progeny of selected parents

Question 39

# Identify Regression coefficient of offspring and one (1) parent

Answer 39

h^2/2

Question 40

# Identify Regression coefficient of offspring and midparent (average of parents)

Answer 40

h^2

Question 41

# Identify Regression coefficient of Monozygotic (MZ) twins

Answer 41

h^2

Question 42

# Identify Correlation coefficient of full siblings

Answer 42

h^2/2

Question 43

# Identify Correlation coefficient of Half siblings

Answer 43

h^2/4

Question 44

# Identify Correlation coefficient of first cousins

Answer 44

h^2/8

Question 45

# Identify regions of DNA which is associated with a particular phenotypic trait

Answer 45

Quantitative Trait Loci (QTL)

Question 46

# Identify Quantitative Trait Loci (QTL) link two types of information:

Answer 46

1. phenotypic data 2. genotypic data

Question 47

# True or False QTLs determine if phenotypic differences are due to a few loci with fairly large effects, or to many loci, each with minute effects

Answer 47

True