Lecture 17

Question 1

continuous variation in phenotype

Answer 1

• height in humans
• mile and meat production in animals
• yield in see protein

Question 2

quantitative inheritance

Answer 2

• continuous variation across range of phenotypes measured and described in quantitative terms

Question 3

quantitative traits

Answer 3

display continuous variation
- measured and described in quantitative terms (quantitative inheritance)

Question 4

polygenic

Answer 4

varying phenotypes result from input of many genes

Question 5

multifactorial or complex traits

Answer 5

result of both gene action and environmental influences

Question 6

polygenic traits that do not show continuous variation

Answer 6

Meristic traits, threshold traits

Question 7

merisitc traits

Answer 7

• phenotype can be recorded by counting whole number
• examples) number of seeds in pods and number of eggs laid by chicken

Question 8

threshold traits

Answer 8

• polygenic and often multifactorial
• have a small number of discrete phenotypic classes
• an increasing number of diseases show this pattern of polygenic inheritance (type II diabetes)

Question 9

quantitative patterns

Answer 9

• mendelian factors could not account for range of phenotypes seen in quantitative patterns of inheritance

Question 10

multiple-gene hypothesis

Answer 10

• many genes, individually behaving in mendelian fashion, contribute to phenotype in cumulative/quantitative way
• example: grain color in wheat

Question 11

multiple-gene hypothesis

Answer 11

additive alleles and non-additive alleles
- various grain color phenotypes due to additive and non-additive allele

Question 12

additive allele

Answer 12

contirbutes equally to red grain color

Question 13

non-additive allele

Answer 13

fails to produce red pigment

Question 14

greater number of additive alleles in genotype

Answer 14

more intense red color expressed in phenotype

Question 15

quantitative loci

Answer 15

• numerous loci can function in similar fashion
• control various quantitative phenotypes
• greater and greater numbers of classes appear in F2 generation in more complex ratios

Question 16

additive alleles are the basis of continuous variation

Answer 16

• contribute to single quantitative character
• phenotypic contribution of each additive allele is approximately equal
• additive alleles together produce substantial phenotypic variation

Question 17

polygenes

Answer 17

• genes contributing to quantitative trait
• number of polygenes (n) contributing to quantitative trait is estimated based on ratio of F2 individuals resembling either of two extreme P1 phenotypes
• 1/4ˆn = ration of F2 individuals expressing either extreme phenotype, where n is equal to the number of polygenes

Question 18

Low number of polygenes (n)

Answer 18

• number of additive loci can be estimated from total number of possible phenotypes
• (2n+1) = number of distinct phenotypic categories observed

Question 19

Heritability

Answer 19

• describes proportion of total phenotypic variation in population due to genetic factors
• however, does no indicate how much of a trait is genetically determined or the extent to which an individual’s phenotype is due to genotype

Question 20

Heritability estimate

Answer 20

• gives proportion of phenotypic variation attributed to genetic variation within a certain population in particular environment
• example: heritability mean of 0.65 human height
  
  • 65% of overall variation in height is due to genotypic difference in individuals
  • not 65% due to genes
    65% of the overall variation of height is due to variation of genotypic differences

Question 21

Phenotypic variance (Vp) components

Answer 21

• genotypic variance
• environemental variance
• genotpye-by-environment interaction variance
• heritability estimates obtained using experimental and statistical techniques, paritiaions Vp into 2 contributing categories: genotypic variance and environmental variance
• nature vs. nurture

Question 22

additive variance

Answer 22

genotypic variance due to additive action of alleles at quantitative trait loci

Question 23

dominance variance

Answer 23

deviation from additive components that results when phenotypic expression in heterozygote not precise

Question 24

interactive variance

Answer 24

deviation from additive components that occurs when two or more loci behave epistatically

Question 25

artificial selection (fast and easy)

Answer 25

- choosing specific individuals with preferred phenotypes from initially heterogeneous population for future breeding - purpose: to develop population containing high frequency of individuals with desired traits

Question 26

artificial trait selection (slow and complex)

Answer 26

- slower and more complex - artificial trait selection can be polygenic and multifactorial

Question 27

traits of economic importance

Answer 27

- crops and livestock - grain yield in plants - weight gain or milk yield in cattle - speed or stamina in horses

Question 28

realized heritability

Answer 28

- selective breeding estimates potential success for artificial selection - ex) artificial selection for increased oil content in corn

Question 29

estimates of narrow-sense heritability...

Answer 29

are expressed as percentage values for traits among different organisms

Question 30

single heritability estimate

Answer 30

only provides information about one population in specific environment

Question 31

concordance

Answer 31

- twins are concordant for a given trait, either both or neither express the trait

Question 32

discordant

Answer 32

one expresses while the other does not - comparison of concordant values (MZ vs. DZ) gives potential value for heritability assessment

Question 33

genetic mapping

Answer 33

when many quantitative trait loci (QTLs) for a given trait are located, a genetic map gives positions of genes involved on different chromosomes

Question 34

quantitative trait loci study

Answer 34

mapping and characterizing quantitative traits in the tomato including fruit shape and weight - identified more than 28 QTLS - a specific gene (ORFX) is responsible for 30% of variation in fruit weight

Question 35

QTLS

Answer 35

- multiple genes contributing to quantitive traits - involves finding associations between DNA markers and phenotypes