Quantitative Genetics and Complex Traits Flashcards
Identify
Traits wherein varying phenotypes are a result from the input of genes at more than one loci
Polygenic traits
Identify
Quantitative traits whose phenotypes result from both gene action and environmental influences
Multifactorial (or Complex) Traits
Identify
Another term for Multifactorial Traits
Complex Traits
Identify
Three categories of traits found to have complex inheritance
- Continuous/quantitative traits
- Meristic traits
- Threshold traits
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.
Multiple-gene hypothesis
True or False
Additive alleles contribute a constant amount to the phenotype
True
True or False
Each additive allele’s contribution to the phenotype is equal
True
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.
A. 1/4^n
Usually these are the F2 offsprings that express the parental phenotype.
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.
n = log (fraction of F2 as extreme as one parent) / log (1/4)
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.
- 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
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.
(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
True or False
Data seen in Polygenic traits form a normal distribution (bell curve)
True
Identify
(1) and (2) of various kinds will cause the distribution curve to appear symmetrical
- Non-additivity
- Interactions
Identify
Aside from non-additivity and interactions, what else is a modification of additive effects?
Dominance between alleles
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
True
Identify
Proportion of total phenotypic variation in a population that is due to genetic factors
Heritability
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.
- Genotypic variance (VG)
- Environmental variance (VE)
- Genotype-by-Environment variance (Vgxe)
True or False
Variation between different inbred strains in a constant environment is due predominantly to genetic factors
True
Identify
Measures the contribution of Genotypic variance (VG) to the total phenotypic variance (VP)
Broad-Sense Heritability (H^2)
Identify
H^2 is equal to
H^2 = VG/VP
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
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.
True or False
Broad-sense Heritability includes all types of genetic variation in the population
True
Identify
All genetic variations in the population
- VD = Dominance-based (Mendelian)
- VI = Epistatic
- VA = Additive
True or False
Broad-Sense Heritability is used as a genetic basis in breeding programs
False; it is Narrow-Sense Heritability that is used in Breeding Programs
Identify
Measures the proportion of phenotypic variance due to additive genotypic variance alone
Narrow-Sense Heritability (h^2)
True or False
VG = VE + VI + VP
False; VG = VI + VA + VD
* Vg = genotypic variance
* Vi = epistatic genotypic variance
* Va = additive genotypic variance
* Vd = dominant genotypic variance
True or False
All phenotypic variance in F1 generation is due to genotypic variance
False; It is due to Environmental Variance
Identify
Variance in the F2 generation is equal to
Vf2 = VG + VE
Identify equation
Genetic variance is equal to:
- Phenotypic variance of F2 generation minus Phenotypic Variance of F1 generation (Vf2 - Vf1)
- [a^2(N)]/2
- 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
Identify equation
Contribution of each additive allele (a) is equal to
a = D/2N
Identify equation
Numerical difference between the two parental means
Hint: derive equations
D = (a)(2)(N)
Identify
All assumptions in variance method
- 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
Identify the equations
Narrow-Sense heritability is equal to:
- Va/Vp
- Va/Ve+Vd+Va
- (M2-M)/(M1-M)
- Correlation Coefficient in monozygotic (MZ) twins
Equation 2- epistatic variance is negligible
True or False
In terms of accuracy, h^2 > H^2
True; thus, h^2 is preferred by breeders.
Identify
Process of Choosing specific individuals with preferred phenotypes from an initially heterogenous population
Artificial Selection
True or False
Narrow-Sense Heritability (h^2) cannot be used to predict the impact of artifical selection
False; it can be used
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
True
Identify
h^2, in terms of mean scores in the population, is equal to
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
Identify
Regression coefficient of offspring and one (1) parent
h^2/2
Identify
Regression coefficient of offspring and midparent (average of parents)
h^2
Identify
Regression coefficient of Monozygotic (MZ) twins
h^2
Identify
Correlation coefficient of full siblings
h^2/2
Identify
Correlation coefficient of Half siblings
h^2/4
Identify
Correlation coefficient of first cousins
h^2/8
Identify
regions of DNA which is associated with a particular phenotypic trait
Quantitative Trait Loci (QTL)
Identify
Quantitative Trait Loci (QTL) link two types of information:
- phenotypic data
- genotypic data
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
True
