Vocab
Another word for quantitative characteristics.
What are continuous characteristics?
When mice mate, their litter size is considered a quantitative trait and represented in whole numbers. This is NOT a qualitative trait because it has influences from both genetics & the environment.
What is a meristic trait (characteristic)?
What is regression? How is it used?
Regression is a mathematical relationship between correlated variables. Regression is used to predict the value of a variable from the value of a correlated variable.
How the broad-sense and narrow-sense heritabilities differ.
What is: the broad-sense heritability is the portion of phenotypic variance that is due to all types of genetic variance, including additive, dominance, and genic interaction variances. The narrow-sense heritability is just that portion of the phenotypic variance due to additive genetic variance.
Two factors that influence response to selection.
What are: narrow sense heritability and how much selection there is?
Another word for qualitative characteristics.
What are discontinuous characteristics?
Susceptibility to a particular disease can be considered a quantitative trait and represented using a binary system of healthy vs. diseased. This is NOT a qualitative trait because it has influences from both genetics & the environment.
What is a threshold characteristic?
Information that the mean and variance provide about a distribution.
What is the mean is the center of the distribution. The variance is how broad the distribution is around the mean.
Equation for total phenotypic variance.
VP = VG + VE+ VGE
Explain how the response to selection often levels off after many generations of selection.
What is: after many generations, the response to selection plateaus because of two factors. First, the genetic variation may be depleted—all the individuals in the population now have the alleles that maximize the quantitative trait; with no genetic variation, there can be no selection or response to selection. Second, even if genetic variation persists, artificial selection may be limited by an opposing natural selection.
Chromosomal regions that contain genes that influence a quantitative trait.
What are QTLs? (quantitative trait loci)
A single trait that is influenced by multiple genes at different loci.
What is a polygenic trait (characteristic)?
How the standard deviation is related to the variance.
What is the standard deviation is the square root of the variance?
All of the components that contribute to the phenotypic variance. Definition of each component.
What is:
VG – Component of variance due to variation in genotype
VA – Component of variance due to additive genetic variance
VD – Component of variance due to dominance genetic variance
VI – Component of variance due to genic interaction variance
VE – Component of variance due to environmental differences
VGE – Component of variance due to interaction between genes and environment
How the response to selection is related to the narrow-sense heritability. How the selection differs.
Information that the response to selection provides.
The response to selection (R) = narrow-sense heritability (h2) × selection differential (S).
The value of R predicts how much the mean quantitative phenotype will change with different selection in a single generation.
Kernel color in a strain of wheat, in which two codominant alleles segregating at a single locus determine the color. Thus, there are three phenotypes present in this strain: white, light red, and medium red. Name the type of trait.
What is a discontinuous (qualitative) characteristic?
(because only a few distinct phenotypes are present and it is determined by alleles at a single locus)
Polygenic characteristics have many phenotypes. Explain.
Many genotypes are possible with multiple genes. Even for the simplest two-allele loci, the number of possible genotypes is equal to 3n, where n is the number of loci or genes. Thus, for 3 genes, we have 27 genotypes, 4 genes yields 81, and so forth. If each genotype corresponds to a unique phenotype, then we have the same numbers of phenotypes: 27 possible phenotypes for 3 genes and 81 possible phenotypes for 4 genes. Finally, the phenotype for a given genotype may be influenced by environmental factors, leading to an even greater array of phenotypes.
Explain the relation between a population and a sample. Characteristics that a sample have to be representative of the population.
What is a sample is a subset of the population?
To be representative of the population, a sample should be randomly selected and sufficiently large to minimize random differences between members of the sample and the population.
Assume that human ear length is influenced by multiple genetic and environmental factors. Suppose you measured ear length on three groups of people, in which group A consists of five unrelated persons, group B consists of five siblings, and group C consists of five first cousins.
a. Assuming that the environment for each group is similar, which group should have the highest phenotypic variance? Explain why.
b. Is it realistic to assume that the environmental variance for each group is similar? Explain your answer.
a. Group A, because unrelated individuals have the greatest genetic variance.
b. No. Siblings from the same family and who are raised in the same house should have smaller environmental variance than group A of unrelated individuals.
Pigs have been domesticated from wild boars. Explain whether you would you expect to find higher heritability for weight among domestic pigs or wild boars.
What is: wild boars will probably have higher heritability than domestic pigs.
Domestic pigs, because of many generations of breeding and selection, are likely to have less variance, and higher degree of homozygosity, for genes that affect commercial traits such as weight.
Briefly explain why the relation between genotype and phenotype is frequently complex for quantitative characteristics.
Quantitative characteristics are polygenic, so many genotypes are possible. Moreover, most quantitative characteristics are also influenced by environmental factors. Therefore, the phenotype is determined by complex interactions of many possible genotypes and environmental factors.
You cross 2 different homozygous varieties of pea plants that differ in height by 24 cm. The F1 progeny are interbred. Of the F2 progeny, 1/1024 of the pea plants are similar to one of the parental plants. This is how many loci with segregating pairs of alleles are contributing to the height difference.
What is 5 loci?
solve for "n": (1/4)^n = (1/1024)
n= 5
(see pgs 688-689)
Information that the correlation coefficient provide about the association between two variables.
Provide examples for values close to +1, -1, & 0.
The magnitude or absolute value of the correlation coefficient reports how strongly the two variables are associated. A value close to +1 or –1 indicates a strong association (positive or negative, respectively); values close to zero indicate weak association. It should be noted that correlation does not mean causation.
Phenotypic variation in tail length of mice has the following components:
Additive genetic variance (VA ) = 0.5
Dominance genetic variance (VD) = 0.3
Genic interaction variance (VI ) = 0.1
Environmental variance (VE ) = 0.4
Genetic-environmental interaction variance (VGE ) = 0.0
a. Determine the narrow-sense heritability of tail length.
b. Determine the broad-sense heritability of tail length.
a. Narrow-sense heritability is VA/VP = 0.5/1.3 = 0.38.
b. Broad-sense heritability is VG/VP = (VA + VD + VI)/VP = 0.9/1.3 = 0.69.
A strawberry farmer determines that the average weight of individual strawberries produced by plants in his garden is 2 g. He selects the 10 plants that produce the largest strawberries; the average weight of strawberries among these selected plants is 6 g. He interbreeds these selected strawberry plants. The progeny of these selected plants produce strawberries that weigh 5 grams. If the farmer were to select plants that produce an average strawberry weight of 4 grams, what would be the predicted weight of strawberries produced by the progeny of these selected plants?
Use the equation R = h^2* S.
R, the response to selection, is the difference between the mean of the starting population and the mean of the progeny of the selected parents. In this case, R = 5 g – 2 g = 3 g. S, the selection differential, is the difference between the mean of the starting population and the mean of the selected parents; in this case S = 6 g – 2 g = 4 g. Substituting in the equation, we get 3 g = h2(4 g); h2 = 0.75. If the selected plants averaged 4 g, then S would be 2 g and R = 0.75(2 g) = 1.5 g. Therefore, the predicted average weight of strawberries from the progeny plants would be 2 g + 1.5 g = 3.5 g.