Ch 17 Quantitative Genetics

Question 1

quantitative genetics

Answer 1

genetic analysis of complex characteristics such as the oil content of corn

Question 2

continuous characteristics

Answer 2

characteristics vary continuously along a scale of measurement
also called quantitative characteristics because any individuals phenotype must be described by a quantitative measurement

Question 3

two phenomena for quantitative characteristics

Answer 3

1) many are polygenic: influenced by genes at many loci
2) often arise when environmental factors affect the phenotype because environmental differences result in a single genotype producing a range of phenotypes

Question 4

multifactorial

Answer 4

most continuously varying characteristics are both polygenic and influenced by environmental factors

Question 5

threshold characteristic

Answer 5

a type of quantitative characteristic that is present or absent
they exhibit only two phenotypes; are determined by multiple genetic and environmental factors

Question 6

frequency distributions

Answer 6

a graph of the frequencies (numbers or proportions) of the different phenotypes

Question 7

normal distribution

Answer 7

many quantitative characteristics exhibit a symmetrical (bell-shaped) curve
arise when a large number of independent factors contribute to a measurement

Question 8

types of distribution

Answer 8

normal, skewed and bimodal

Question 9

mean

Answer 9

also called the average, is a statistic that provides information about the center of a distribution

Question 10

variance

Answer 10

indicates the variability of a group of measurements, or how spread out the distribution is
the larger the variance, the greater the spread of measurements in a distribution around its mean

Question 11

heritability

Answer 11

proportion of the total phenotypic variation that is due to genetic differences
if increased, then largely genetic
if decreased, then largely enviromental

Question 12

phenotypic variation

Answer 12

represented Vp
we could collect a representative sample of plants from the population, weigh each plant in the sample, and calculate the mean and variance of plant weight

Question 13

genetic variance

Answer 13

represented Vg

differences in genotypes among individual members of the population

Question 14

environmental variance

Answer 14

represented Ve
differences in phenotype may be due to environmental differences among the plants
includes differences in environmental factors such as the amount of light or water that the plant receives; it also includes random differences in development that cannot be attributed to any specific factor

Question 15

genetic-environmental interaction variance

Answer 15

represented Vge

arises when the effect of a gene depends on the specific environment in which it is found

Question 16

additive genetic variance

Answer 16

represented Va
comprises the additive effects of genes on the phenotype, which can be summed to determine the overall effect on the phenotype
primarily determines the resemblance between parents and offspring

Question 17

dominance genetic variance

Answer 17

represented Vd
the effects of some genes have a dominance component
the effect of an allele depends on the identity of the other allele at that locus

Question 18

gene interaction variance

Answer 18

represented Vi

genes at different loci may interact in the same way that alleles at the same locus interact

Question 19

broad-sense heritability

Answer 19

represented H^2
represents the proportion of phenotypic variance that is due to genetic variance
H^2 = 1 then all your phenotypic variance is due to genetic variance
H^2 = 0 then little phenotypic variance, it is due to environment

Question 20

narrow-sense heritability

Answer 20

represented h^2

equal to the additive genetic variance divided by the phenotypic variance

Question 21

limitations of heritability

Answer 21

1. Does not indicate the degree to which a characteristic is genetically determined
2. an individual does not have heritability
3. no universal heritability for a characteristic
4. even when heritability is high, environmental factors can influence a characteristic
5. heritabilities indicate nothing about the nature of population differences in a characteristic

Question 22

quantitative trait loci (QTLs)

Answer 22

chromosome regions with genes that control polygenic characteristics
a map location for a chromosome region that is associated with a quantitative trait

Question 23

natural selection

Answer 23

arises through the differential reproduction of individuals with different genotypes

Question 24

artificial selection

Answer 24

humans have practiced a form of selection by promoting the reproduction of organisms with traits perceived as desirable

Question 25

response to selection

Answer 25

the extent to which a characteristic subjected to selection changes in one generation
represented by R and is the difference between the original population and offspring
R= offspring - original population

Question 26

selection differential

Answer 26

the response to selection thus depends on the degree to which the selected parents differ from the rest of the population
defined as the difference between the mean phenotype of the selected parents and the mean phenotype of the original population
S= breeding parents - original population

Question 27

realized heritability

Answer 27

heritability determined by a response-to-selection experiment
if certain assumptions are met, this is identical to narrow-sense heritability

Question 28

standard deviation

Answer 28

expressing deviation from mean in same scale of measurement mean