Quantitative Genetics

Question 1

Define quantitative traits

Answer 1

traits that have continuous distribution and are not discrete
ex. range of reds to pinks
they are controlled by genotype at multiple loci and by the environment

Question 2

What are East’s 2 predictions

Answer 2

1. unless N is large in F2, (meaning in small population size) parental phenotypes will not be observed
2. with selection parental phenotypes can be obtained in later generations, because parental phenotypes are there but are just hidden in heterozygotes

Question 3

The rarest phenotype has what genotype

Answer 3

homozygous genotypes

Question 4

Why is there a range of parental phenotypes to begin with

Answer 4

because all genotypes have some sort of environmental influence so although the same genotype, environment causes changes in genotype and therefore different phenotypes, a range

Question 5

What is a quantitative trait loci

Answer 5

genetic regions that influence phenotypic variation of a quantitative trait and with the effects of the environment
ex. loci responsible for human height

Question 6

What is involved in QTL mapping

Answer 6

1. physically locating the genes (the region of the chromosome associated with the trait)
2. identifying candidate loci (what chromosomes could be responsible, potentials).
   [step 1 = region step 2 = candidates]

Question 7

What is fishers theory in terms of QTLs

Answer 7

that all alleles fixed by selection have a little/subtle effect on the phenotype

Question 8

What is orrs theory in terms of QTLs

Answer 8

some fixed alleles have large phenotypic effects

Question 9

If QTL and the marker were linked =
vs. if QTL and marker not linked =

Answer 9

disequilibrium
equilibrium

Question 10

How does F2 phenotype distribution differ if marker and QTL are linked vs. not linked

Answer 10

if linked = have lower, middle, and high distribution
if not linked = have equal distribution of them all in the middle

Question 11

If the majority of QTLs were explained then what theory is right

Answer 11

if majority of QTLs were explained then means that Orr is right because

Question 12

Using quantitative genetics we can figure out what 3 steps

Answer 12

1. measure heritability of variation
2. fitness differential (strength of selection)
   and both can be used to figure out
3. to predict response to selection

Question 13

phenotypic variation can be driven by both ___ and ____
what equation represents this

Answer 13

genotype and environment
Vp=Vg+Ve

Question 14

Define broad-sense heritability (h)
what equation

Answer 14

is the amount of phenotypic variation that is caused by genetics
h = Vg/Vp = Vg/Vg=Ve

Question 15

Total genetic variation includes what 3 effects (and describe each)
what equation

Answer 15

additive = (largest component of Vg) additive effect of many genes
dominance =
interactive effects = how they interact with each other and the environment
Vg = Va+Vd+Vi

Question 16

define narrow sense heritability (h2)

Answer 16

the amount of phenotypic variation due to additive genetic variance (measures potential response to selection)
h2 = Va/Vp

Question 17

The slope of midoffspring values vs midparent values represents what

Answer 17

estimate of heritability (h2) -h2 will be between 0-1 (0=none, 1 = all)
allows us to predict how a population will response to selection

Question 18

Why cant we just measure heritability by measuring parents and offspring

Answer 18

because individuals of same species will also be similar because of environments

Question 19

What does strength of selection mean

Answer 19

difference between mean of selected individuals and the mean of the entire population
S = t-t
t = average of selected, t = average of all

Question 20

What does the predicting response to selection involve

Answer 20

quantify heritability and the effect of selection (R)
R = h2S or h2 = R/S