Deck 23: Quantitative Genetics and Multifactorial Traits

Question 1

If the proportion of F₂ individuals resembling either of the two most extreme phenotypes (the parental phenotypes) can be determined, what formula can be applied to determine the number of gene pairs involved?

Answer 1

1/4ⁿ (where n is the number of gene pairs)

Question 2

What formula can be used to determine the number of categories (phenotypes) possible in the F₂ results of a polygenic system?

Answer 2

2n + 1 (where n is the number of gene pairs)

Question 3

What are the name and formula for describing sample variability?

Answer 3

variance; s² = S (X_i - X)²/n - 1

Question 4

What is the term given to a random subset of individuals who are selected for measurement in a particular study?

Question 5

Assume that four polygenic gene pairs are involved in determining phenotypes of F₂. How many phenotypic classes are expected?

Question 6

Characteristics exhibited by continuously varying traits include ________.

A) sex-linked genes only
B) autosomal genes only
C) quantification by measuring, weighing, counting, etc.
D) a 9:3:3:1 ratio
E) 3:1 and 1:1 ratios

Question 7

Continuous inheritance is often related to the term quantitative inheritance. Why?

Question 8

Provide a brief description of discontinuous inheritance and continuous inheritance. How are the two related? How are they different?

Question 9

Quantitative inheritance involves the interaction of a number of gene loci. The pattern of genetic transmission typical of quantitative inheritance is ________.

A) discontinuous distributions such as 3:1
B) typical of Mendelian inheritance
C) continuous variation of phenotypic expression
D) a 9:3:3:1 ratio
E) usually a pattern that clearly reflects dominance and recessiveness

Question 10

How many gene pairs are involved in generating a typical 1:4:6:4:1 ratio?

Question 11

Assume that a cross is made between tall and dwarf tobacco plants. The F₁ generation showed intermediate height, while the F₂ generation showed a distribution of height ranging from tall to dwarf, like the original parents, and many heights between the extremes. These data are consistent with which one of the following modes of inheritance?

A) multiple-factor inheritance
B) alternation of generations
C) codominance
D) incomplete dominance
E) hemizygosity

Question 12

The 9:3:3:1 ratio is typical of a dihybrid cross in which complete dominance and independent assortment occur. What is the dihybrid ratio with independent assortment of polygenes?

Question 13

Assume that in the F₂ of a series of crosses, 1/64 of the offspring resemble one of the parents (P). How many gene pairs are involved in producing these results?

Question 14

When a trait is polygenic, but distinguished from continuous and meristic traits by having a small number of discrete classes, it is said to be a(n) ________ trait.

Question 15

Bell-shaped distributions produced by plotting results of F₂ and F₃ crosses are typical of which type of inheritance?

A) multiple-factor inheritance
B) alternation of generations
C) codominance
D) incomplete dominance
E) hemizygosity

Question 16

Environmental factors typically influence inheritance of ________.

A) multiple alleles
B) codominance
C) trihybrid crosses
D) polygenic traits
E) dominantly inherited traits

Question 17

List at least three statistical values often used to represent a sample.

Question 18

Assume that you are studying a trait determined by a number of polygenes. If there are seven phenotypic categories, how many genes are probably involved?

Question 19

Given the following numbers, calculate the mean: 10, 12, 14, 16, 18.

Question 20

In the early part of the twentieth century, Nilsson-Ehle and others described experiments showing that multiple loci may be involved in the inheritance of certain traits. Such patterns are often called ________.

Question 21

We often refer to the host of genetic factors in the genome that have an influence on a particular gene's expression as its genetic background. What influence does genetic background have over the phenotype of the organism?

Question 22

What is the formal expression used to examine the relative importance of genetic versus environmental factors?

Question 23

Huntington disease is inherited in humans as an autosomal dominant gene. Affected individuals show progressive brain deterioration from cell death in the cerebral cortex. Onset of the disease usually occurs between ages 30 and 50. Give two possible reasons for the observed variation in the age of onset of this disease.

Question 24

Name two mammalian traits with relatively high heritability (h²) values and two with relatively low h² values.

Question 25

What is the relationship between the narrow-sense heritability (h²) index and the impact of selection?

Question 26

Name two human traits that would be expected to have high concordance.

Question 27

Provide a formal equation for h² (narrow-sense heritability).

Question 28

Individuals with the same genetic background and a high degree of homozygosity are said to be isogenic. Of what value are isogenic strains in genetic studies?

Question 29

Interpret the meaning of an H² (broad-sense heritability) value that approaches 0.0.

Question 30

List at least two statistical terms commonly used in the analysis of quantitative traits.

Question 31

To estimate how much the means of a variety of like samples drawn from the same population might vary, what statistic is often used and what is the formula for it?

Question 32

Describe the value of using twins in the study of questions relating to the relative impact of heredity versus environment.

Question 33

Interpret the meaning of an H² (broad-sense heritability) value that approaches 1.0.

Question 34

Provide a brief definition of the terms additive variance, dominance variance, and interactive variance.

Question 35

What is meant by the term heritability? Describe the components of heritability and provide a brief explanation of each. Of what interest is heritability to animal and plant breeders?

Question 36

Name the three components of phenotypic variance.

Question 37

As used in twin studies in mammals, distinguish between the terms concordant and discordant.

Question 38

Define the term broad-sense heritability (H²⁾. What is implied by a relatively high value of H²? Express aspects of broad-sense heritability in equation form

Question 39

If one is attempting to determine the influence of genes or the environment on phenotypic variation, inbred strains with individuals of a relatively homogeneous or constant genetic background are often used. Variation observed between different inbred strains reared in a constant or homogeneous environment would likely be caused by genetic factors. What would be the source of variation observed among members of the same inbred strain reared under various environmental conditions?

Question 40

What is the name of the process of selecting a specific group of organisms from an initially heterogeneous population for future breeding purposes?

Question 41

Which two relatively recent extensions to QTL mapping center on molecular definitions of phenotypes with quantitative traits?

Question 42

Additive alleles are those that are epistatic over nonallelic genes that influence the same phenotypic characteristic.

Question 43

In the analysis of quantitative traits, positions on chromosomes called quantitative trait loci (QTLs) are often discussed. In the same context, restriction fragment length polymorphisms (RFLPs) are also discussed. What is the relationship between QTLs and RFLPs?

Question 44

Concordance refers to the frequency with which members of a twin pair express a different trait.

Question 45

How would the use of a large series of monozygotic and dizygotic twins enhance studies on the genetic basis of human behavior?

Question 46

Heritability is a measure of the degree to which the phenotypic variation of a given trait is due to genetic factors.

Question 47

The multiple factor hypothesis suggests that many factors or genes contribute to the phenotype in a cumulative or quantitative manner.

Question 48

Polygenes are involved in determining continuously varying or multiple-factor traits.

Question 49

Typically, one thinks of identical (MZ) twins being genetically identical. However, genomic differences do exist between MZ twins by epigenetic processes. What are epigenetic processes?

Question 50

A "marker" in a genetic sense usually represents a site along a chromosome where a specific nucleotide sequence exists. What specific phrase is used when such markers are identified by restriction endonucleases and a particular set of DNA fragments is generated?

Question 51

Traits such as height, general body structure, skin color, and some behavioral traits are probably caused primarily by genes that behave codominantly or epistatically.

Question 52

What are QTLs and RFLPs?