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BIO 140: Population Genetics > Quantitative Genetics and Complex Traits > Flashcards

Quantitative Genetics and Complex Traits Flashcards

1
Q

Identify

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

A

Polygenic traits

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2
Q

Identify

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

A

Multifactorial (or Complex) Traits

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3
Q

Identify

Another term for Multifactorial Traits

A

Complex Traits

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4
Q

Identify

Three categories of traits found to have complex inheritance

A
  1. Continuous/quantitative traits
  2. Meristic traits
  3. Threshold traits
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5
Q

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.

A

Multiple-gene hypothesis

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6
Q

True or False

Additive alleles contribute a constant amount to the phenotype

A

True

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7
Q

True or False

Each additive allele’s contribution to the phenotype is equal

A

True

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8
Q

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

A. 1/4^n

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

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9
Q

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.

A

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

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10
Q

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.

A
  • 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
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11
Q

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.

A

(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

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12
Q

True or False

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

A

True

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13
Q

Identify

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

A
  1. Non-additivity
  2. Interactions
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14
Q

Identify

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

A

Dominance between alleles

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15
Q

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

A

True

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16
Q

Identify

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

A

Heritability

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17
Q

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.

A
  1. Genotypic variance (VG)
  2. Environmental variance (VE)
  3. Genotype-by-Environment variance (Vgxe)
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18
Q

True or False

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

A

True

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19
Q

Identify

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

A

Broad-Sense Heritability (H^2)

20
Q

Identify

H^2 is equal to

A

H^2 = VG/VP

21
Q

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

A

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.

22
Q

True or False

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

A

True

23
Q

Identify

All genetic variations in the population

A
  • VD = Dominance-based (Mendelian)
  • VI = Epistatic
  • VA = Additive
24
Q

True or False

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

A

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

25
Q

Identify

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

A

Narrow-Sense Heritability (h^2)

26
Q

True or False

VG = VE + VI + VP

A

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

27
Q

True or False

All phenotypic variance in F1 generation is due to genotypic variance

A

False; It is due to Environmental Variance

28
Q

Identify

Variance in the F2 generation is equal to

A

Vf2 = VG + VE

29
Q

Identify equation

Genetic variance is equal to:

A
  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

30
Q

Identify equation

Contribution of each additive allele (a) is equal to

A

a = D/2N

31
Q

Identify equation

Numerical difference between the two parental means

Hint: derive equations

A

D = (a)(2)(N)

32
Q

Identify

All assumptions in variance method

A
  • 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
33
Q

Identify the equations

Narrow-Sense heritability is equal to:

A
  1. Va/Vp
  2. Va/Ve+Vd+Va
  3. (M2-M)/(M1-M)
  4. Correlation Coefficient in monozygotic (MZ) twins

Equation 2- epistatic variance is negligible

34
Q

True or False

In terms of accuracy, h^2 > H^2

A

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

35
Q

Identify

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

A

Artificial Selection

36
Q

True or False

Narrow-Sense Heritability (h^2) cannot be used to predict the impact of artifical selection

A

False; it can be used

37
Q

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

A

True

38
Q

Identify

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

A

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

39
Q

Identify

Regression coefficient of offspring and one (1) parent

A

h^2/2

40
Q

Identify

Regression coefficient of offspring and midparent (average of parents)

A

h^2

41
Q

Identify

Regression coefficient of Monozygotic (MZ) twins

A

h^2

42
Q

Identify

Correlation coefficient of full siblings

A

h^2/2

43
Q

Identify

Correlation coefficient of Half siblings

A

h^2/4

44
Q

Identify

Correlation coefficient of first cousins

A

h^2/8

45
Q

Identify

regions of DNA which is associated with a particular phenotypic trait

A

Quantitative Trait Loci (QTL)

46
Q

Identify

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

A
  1. phenotypic data
  2. genotypic data
47
Q

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

A

True

BIO 140: Population Genetics (1 decks)

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