Question 1

Which of the following best describes the difference between discontinuous and continuous phenotypic variation?

Accepted Answer

Discontinuous variation allows organisms to be assigned to sharply distinguishable categories, while continuous variation shows a range of values in an uninterrupted continuum.

Question 2

Human height is considered a multifactorial trait. Which statement best explains why?

Accepted Answer

It is influenced by multiple genes and environmental factors, resulting in continuous variation.

Question 3

In the context of polygenic traits, what is a 'major gene'?

Accepted Answer

A gene whose alleles have a strong influence on the phenotype compared to other contributing genes.

Question 4

Which formula correctly calculates the number of phenotypic categories for a polygenic trait with $n$ additive genes, each with two alleles?

Accepted Answer

$2n + 1$

Question 5

Nilsson-Ehle’s wheat kernel color experiment supported the multiple-gene hypothesis. What was the key finding?

Accepted Answer

Kernel color showed five phenotypic classes in the $F_2$ generation, consistent with two additive genes.

Question 6

Edward East’s experiment with Nicotiana longiflora corolla length led to which two major conclusions?

Accepted Answer

Corolla length is based on segregation of alleles of multiple genes and is influenced by environmental factors.

Question 7

Which equation is used to calculate the variance ($s^2$) of a quantitative trait in a sample?

Accepted Answer

$s^2 = \sum (x_i - \bar{x})^2 / df$

Question 8

In a population where all individuals are homozygous for alleles controlling a trait, what is the value of genetic variance ($V_G$)?

Accepted Answer

$V_G = 0$

Question 9

Which of the following best describes broad sense heritability ($H^2$)?

Accepted Answer

It estimates the proportion of phenotypic variation due to total genetic variation.

Question 10

If the phenotypic variance ($V_P$) in $F_2$ fish is $0.563$ cm$^2$ and the environmental variance ($V_E$) measured in $F_1$ fish is $0.057$ cm$^2$, what is the broad sense heritability ($H^2$)?

Accepted Answer

$H^2 = (0.563 - 0.057) / 0.563 = 0.899$

Question 11

Which of the following is a source of error that can lead to inaccurately high heritability estimates in twin studies?

Accepted Answer

Greater similarity of treatment of monozygotic twins compared to dizygotic twins.

Question 12

What does a concordance value of 100% for a trait in monozygotic twins indicate?

Accepted Answer

The trait is entirely determined by genetic factors.

Question 13

Which formula is used to estimate the response to selection ($R$) in artificial selection experiments?

Accepted Answer

$R = S 	imes h^2$

Question 14

Which mode of selection is most likely to increase phenotypic variance and potentially split a population into two distinct groups?

Accepted Answer

Disruptive selection

Question 15

What is a quantitative trait locus (QTL)?

Accepted Answer

A gene that contributes to phenotypic variation in a quantitative trait.

Question 16

In QTL mapping, what does a significant lod score indicate?

Accepted Answer

There is a QTL linked to the genetic marker being analyzed.

Question 17

Genome-wide association studies (GWAS) are used to:

Accepted Answer

Statistically test for marker variants associated with phenotypic variation across the entire genome.

Question 18

A mutation in the CARD15 gene (3020insC) associated with Crohn’s Disease results in:

Accepted Answer

A protein with diminished activity due to a frameshift and premature stop codon.

Question 19

Which of the following best describes a threshold trait?

Accepted Answer

A polygenic or multifactorial trait with continuous genetic liability, but phenotypes divided into distinct categories based on a threshold.

19.Genetic Analysis of Quantitative Traits

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