Chapter 28 - Complex and Quantitative Traits Flashcards by FRANCES CASALINO

These are characteristics that are determined by several genes are significantly influenced by environmental factors

Complex traits

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Most complex traits are these - traits that can be described numerically

Quantitative traits

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This is the study of the mode of inheritance of complex and quantitative traits

Quantitative genetics

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What are four types of quantitative traits?

Anatomical, physiological, behavioral, disease

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Some quantitative traits are these - can be expressed in whole numbers

Meristic traits

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Diseases are often this type of quantitative trait - traits that are inherited due to the contributions of many genes

Threshold traits

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Do quantitative traits naturally fall into a small number of discrete categories?

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This is an alternative way to describe quantitative traits

Frequency distribution

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How is a frequency distribution for a quantitative trait constructed?

Trait is divided arbitrarily into a number of discrete phenotypic categories

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Frequency distributions for quantitative trait often form this type of distribution

Normal distribution

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These two scientists showed that many traits in animals are quantitative

Francis Galton and Karl Pearson

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Francis Galton and his student Karl Pearson founded this field of genetics to study quantitative traits in animals

Biometric field of genetics

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Genetics is often interested in the amount of this that exists in a group

Phenotypic variation

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A common way to evaluate variation within a population is with a statistic called this

Variance

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Why are variances very important in the analysis of quantitative traits?

They are additive under certain conditions

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The variances of genetic and environmental factors that contribute to a quantitative trait can be added to predict this

Total variation for that trait

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Taking the square root of the variance is a statistic called this

Standard deviation

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If the values in a population follow a normal distribution, then it is easier to appreciate the amount of variation by considering this

Standard deviation

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In many biological problems it is useful to compare these

Two different variables

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This describes the degree of variation between two variables within a group

Covariance

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To calculate this statistic, the covariance needs to be determined first

Correlation coefficient

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Correlation coefficient evaluates this

Strength of association between two variables

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What is the range of values for the correlation coefficient?

+1 to -1

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What does a correlation coefficient of > 0 indicate?

As one factor increases, the other factor will increase with it

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What does a correlation coefficient of 0 indicate?

The two factors are not related

What does a correlation coefficient of < 0 indicate?

As one factor increases, the other factor will decrease

What is the null hypothesis for testing correlation?

There is no real correlation

Like the chi square value, the significance of the correlation coefficient is directly related to these two factors

Sample size and degrees of freedom

What are two assumptions that must be met to make correlation testing valid?

1. The values of X and Y are obtained by an unbiased sampling of the entire population; 2. The scores of X and Y follow a normal distribution and that the relationship between X and Y is linear

Most quantitative traits are this, meaning they are influenced by two or more genes and exhibit a continuum of phenotypic variation

Polygenic

This refers to the transmission of traits that are governed by two or more genes

Polygenic inheritance

This Swedish scientist studied polygenic inheritance in oats and wheat

H. Nilsson-Ehle

Many polygenic traits are especially difficult or impossible to categorize into several discrete genotypic categories when these two things are true

1. The number of genes controlling the trait increases (3 or more); 2. The influence of the environment increases

Can a Punnett square be used to analyze most quantitative traits?

This is the location on a chromosome that harbors one or more genes that affect the outcome of a quantitative trait

Quantitative trait locus (QTL)

This is the basis for quantitative trait locus (QTL) mapping

Association between genetically determined phenotypes for quantitative traits and molecular markers

These are used as reference points along chromosomes and can be RFLPs or microsatellites

Molecular markers

The general strategy for QTL mapping involves this

Two different, highly inbred strains of a diploid species

In QTL mapping, the inbred strains of a diploid species must be different in these two important ways

1. Differ in quantitative trait of interest (i.e., large vs small fruit); 2. Differ in many molecular markers

Can a geneticist ever actually determine the relative amount of a quantitative trait that is controlled by genetics vs the environment?

Instead of determining how much genetics vs the environment control a quantitative trait, geneticists focus on how this will affect the phenotypic results

Variation

To study quantitative trait variation, both of these variances must be considered

Genetic variance (V_G) and Environmental variance (V_E)

Variance due to interactions between genetic environmental factors is expressed as this

V_GxE

Variance due to associations between genetic and environmental factors is expressed as this

V_G<->E

V_GxE expresses variance due to these between genetic and environmental factors

Interactions

V_G<->E expresses variance due to these between genetic and environmental factors

Associations

What is the expression for phenotypic variance?

V_P = V_G + V_E

In the expression for phenotypic variance, what does V_P stand for?

Total phenotypic variance

In the expression for phenotypic variance, what does V_G stand for?

Relative amount of variance due to genetic variation

In the expression for phenotypic variance, what does V_E stand for?

Relative amount of variance due to environmental factors

To study phenotypic variance, these two assumptions may be made

1. Genetic and environmental factors are the only two components that determine a trait; 2. These factors are independent of one another

This is when genetics and environment interact

Genotype-environment interaction

This is when certain genotypes are preferentially found in a particular environment

Genotype-environment association

Is genotype-environment association very common in human genetics?

Yes

What are two ways to correct for genotype-environment association when studying human genetics?

1. Looking at identical vs fraternal twins; 2. Looking at siblings adopted by different families

This is the amount of phenotypic variation within a group of individuals that is due to genetic variation

Heritability

If all the phenotypic variation in a group was due to genetic variation, heritability would have a value of this

If all the phenotypic variation in a group was due to environmental factors, heritability would have a value of this

What are the two types of heritability?

Broad sense and narrow sense

This type of heritability takes into account different types of genetic variation that may affect the phenotype

Broad sense heritability

Geneticists usually subdivide V_G into these three different genetic categories

1. Variance due to additive effects of alleles (V_A); 2. Variance due to alleles that follow a dominant/recessive pattern of inheritance (V_D); Variance due to the effects of alleles that interact in an epistatic manner (V_I)

This type of heritability only takes into account the additive effects of alleles

Narrow sense heritability

Which category of genetic variance do geneticists usually focus on in analyzing quantitative traits?

V_A (variance due to alleles)

What are the three steps in estimating narrow sense heritability?

1. Measure a quantitative trait among groups of genetically related individuals; 2. Use data to compute correlation between individuals; 3. Calculate narrow sense heritability as ℎ_𝑁^2 = 𝑟_obs/𝑟_exp

What is the expression for calculating narrow sense heritability?

ℎ_𝑁^2 = 𝑟_obs /𝑟_exp

What does r_obs represent in the calculation for narrow sense heritability?

Observed phenotypic correlation between related individuals

What does r_exp represent in the calculation for narrow sense heritability?

Expected correlation based on known genetic relationship

For siblings that aren't identical twins, what does r_exp equal?

0.5

For identical twins, what does r_exp equal?

1.0

For parent-offspring relationships, what does r_exp equal?

0.5

For an uncle-niece relationship, what would r_exp equal?

0.25

This scientist was the first to study human fingerprint patterns

Francis Galton

This scientist made human fingerprint patterns more amenable to genetic studies

Kristine Bonnevie

Kristine Bonnevie developed a method for counting these within a human fingerprint

Dermal ridges

What are the three categories of human fingerprint patterns?

Arch, loop, whorl

What is the primary difference between different fingerprint patterns?

Presence/number of triple junctions

Triple junctions in human fingerprints are also known as this

Triradius

This type of fingerprint pattern has no triradius

Arch

This type of fingerprint pattern has 1 triradius

Loop

This type of fingerprint pattern has 2 triradii

Whorl

This is the modification of phenotypes in plant and animal species of economic importance by human intervention

Selective breeding

This is another term for selective breeding

Artificial selection

This type of selection is due to natural variation in reproductive success

Natural selection

This is a consequence of inbreeding in which genetic variation within a group is reduced and homozygosity for deleterious alleles is increased

Inbreeding depression

Quantitative traits are often at this value in unselected populations

Intermediate

This is the point at which selective breeding will have no additional effect, as the population is monomorphic for all or most of the desirable alleles

Selection limit

Response to selection is a common way to estimate this heritability

Narrow sense heritability

This is the response to selection estimated by narrow sense heritability

Realized heritability

What is the expression for calculating realized heritability?

ℎ_𝑁^2 = 𝑅/𝑆

What does R stand for in the calculation for realized heritability?

Response in the offspring to selection (difference between mean of offspring and mean of starting population)

What does S stand for in the calculation for realized heritability?

Selection differential in parents (difference between mean of parents and mean of starting population)

This is when two different inbred strains are crossed to each other and the offspring are more vigorous than either parent

Heterosis (or hybrid vigor)

What are the two major hypotheses to explain heterosis?

Dominance hypothesis and overdominance hypothesis

This scientist proposed the dominance hypothesis in 1908 to explain the genetic basis for heterosis

Charles Davenport

These two scientists proposed the overdominance hypothesis in 1908 to explain the genetic basis for heterosis

George Shull and Edward East