Quantitative Genetics, Evolution, and Population Genetics

Question 1

What is continuous variation in relation to phenotypes?

Answer 1

• continual range of multiple phenotypes
• measured as quantitative inheritance
• e.g. height in humans, milk production in cattle
• the phenotypes result from genes at many loci, so the traits are polygenic (of many genes)

Question 2

What is the multiple-factor or multiple-gene hypothesis?

include the use of additive vs non additive alleles

Answer 2

many genes, each individually behaving in Mendelian fashion, contribute to the phenotype in a cumulative or quantitative way
* locus can be occupied by an additive allele (contributes a constant amount to the phenotype)
* or by a non additive allele (does not contribute quantitatively to phenotype)

Question 3

What is heritability?

explain the difference between high vs. low heritability

Answer 3

used to describe the proportion of total phenotypic variation in a population that is due to genetic factors
high heritability of multifactorial trait: variation is attributed to genetic factors, environment has less impact
low heritability: environmental factors likely have a greater impact on phenotypic variation

Question 4

What is phenotypic variance?

Answer 4

the variability in phenotypes that exists in a population
* can be subdivided into genotypic variance, environmental variance, and genotype-by-environment variance

Question 5

What is Broad-Sense Heritability?

Answer 5

measures the contribution of the genotypic variance to the total phenotypic variance

Question 6

What is Narrow-Sense Heritability?

Answer 6

the proportion of phenotypic variane due to additive genotypic variance alone

Question 7

What are additive, dominance, and interactive variance?

Answer 7

• additive: genotypic variance due to the additive action of alleles at quantitative trait loci
• dominance: deviation from the additie components that results when phenotypic expression in heterozygous is not precisely intermediate between the two homozygotes
• interactive: deviation from the additive components that occurs when two or more loci behave epistatically

Question 8

What are the limitations of heritability studies?

Answer 8

• heritability provides no information about what genes are involved in traits
• measured in populations, limited application to individuals
• depends on the environmental variation

Question 9

What is the Hardy-Weinberg Law?

and name the equation that goes along with it.

Answer 9

describes what happens to allele and genotype frequencies in an ideal population that is infinitely large, randomly mating, and not subject to evolutionary forces such as migration, mutation, or selection
p^2 + 2pq + q^2= 1
A is p
a is q

Question 10

What is the neutral theory of molecular evolution?

Answer 10

mutations leading to amino acid substitutions are usually detrimental with only a very small fraction being favorable
* some mutations are neutral
* some mutations that are favorable or detrimental are preserved or removed from the population by natural selection

Question 11

What is the difference between a population and gene pool?

Answer 11

• a population is a group if individuals belonging to the same species that live in a defined geographical area and actually or potentially interbreed
• a gene pool is the genetic information carried by members of a population

Question 12

What is microevolution vs. macroevolution?

Answer 12

• microevolution is the evolutionary change within populations of a species
• macroevolution is the evolutionary events leading to the emergence of new species and other taxonomic groups

Question 13

What is speciation? How does it occur?

Answer 13

• the formation of new species
• facilitated by environmental diversity
• if a population is spread over a geographic range with subenvironments and different selection pressures, the populations may adapt over time and become distinct from one another

Question 14

What do twin studies tell us about heritability?

Answer 14

• monozygotic (identical) twins are derived from a single zygote that divides and then spontaneously splits into two separate cells
• dizygotic (fraternal) twins originate from two separate fertilization events
• phenotypic changes between pairs of MZ twins will be equivalent to the environmental variance (there is no genetic variance)
• phenotypic variances between DZ twins display both Ve and Vg

Question 15

What is concordance/discordance in twins?

Answer 15

• concordant twins both express a trait or both do not express a trait
• discordant twins are if one expresses a trait and the other does not
• concordance values in MZ twins give us clues that a trait has a strong genetic component

Question 16

What is artificial selection?

Answer 16

the process of choosing specific individuals with preferred phenotypes from an initially heterogeneous population for future breeding purposes

Question 17

Why is narrow-sense heritability valuable to a breeder?

Answer 17

• narrow-sense heritability estimates give the breeder an estimate of how much of the total phenotypic variance is due to addititve genetic variance
• quantitative trait alleles with addititve impact are most easily manipulated by the breeder

Question 18

What is the selection response and selection differential in artificial selection?

Answer 18

• selection response: the degree of response to mating the selected parents
• selection differential: the difference between the mean for the whole population and the mean for the selected population