Chapter 28 - Complex and Quantitative Traits Flashcards
These are characteristics that are determined by several genes are significantly influenced by environmental factors
Complex traits
Most complex traits are these - traits that can be described numerically
Quantitative traits
This is the study of the mode of inheritance of complex and quantitative traits
Quantitative genetics
What are four types of quantitative traits?
Anatomical, physiological, behavioral, disease
Some quantitative traits are these - can be expressed in whole numbers
Meristic traits
Diseases are often this type of quantitative trait - traits that are inherited due to the contributions of many genes
Threshold traits
Do quantitative traits naturally fall into a small number of discrete categories?
No
This is an alternative way to describe quantitative traits
Frequency distribution
How is a frequency distribution for a quantitative trait constructed?
Trait is divided arbitrarily into a number of discrete phenotypic categories
Frequency distributions for quantitative trait often form this type of distribution
Normal distribution
These two scientists showed that many traits in animals are quantitative
Francis Galton and Karl Pearson
Francis Galton and his student Karl Pearson founded this field of genetics to study quantitative traits in animals
Biometric field of genetics
Genetics is often interested in the amount of this that exists in a group
Phenotypic variation
A common way to evaluate variation within a population is with a statistic called this
Variance
Why are variances very important in the analysis of quantitative traits?
They are additive under certain conditions
The variances of genetic and environmental factors that contribute to a quantitative trait can be added to predict this
Total variation for that trait
Taking the square root of the variance is a statistic called this
Standard deviation
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
In many biological problems it is useful to compare these
Two different variables
This describes the degree of variation between two variables within a group
Covariance
To calculate this statistic, the covariance needs to be determined first
Correlation coefficient
Correlation coefficient evaluates this
Strength of association between two variables
What is the range of values for the correlation coefficient?
+1 to -1
What does a correlation coefficient of > 0 indicate?
As one factor increases, the other factor will increase with it
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?
- 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
- 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?
No
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
- 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?
No
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
- 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?
- 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
1
If all the phenotypic variation in a group was due to environmental factors, heritability would have a value of this
0
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
- 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?
- Measure a quantitative trait among groups of genetically related individuals; 2. Use data to compute correlation between individuals; 3. Calculate narrow sense heritability as β_π^2 = π_obs/π_exp
What is the expression for calculating narrow sense heritability?
β_π^2 = π_obs /π_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 arenβt 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?
β_π^2 = π /π
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
