Lecture 13

Question 1

in directional selection, describe how the frequency of a common dominant allele changes over generations?

Answer 1

the allele is SEEN in heterozygote so selection can act faster and the frequency increases quickly

Question 2

in directional selection, describe how the frequency of a recessive and rare allele changes over generations?

Answer 2

the allele is HIDDEN in heterozygotes so selection acts slower and the frequency increases slowly

Question 3

What is selective sweep?

Answer 3

elements close to a selected allele are inherited with the allele because things close-by don’t recombine

Question 4

how does selective sweep affect diversity? why?

Answer 4

selective sweep reduces diversity because multiple elements in the genome are carried thru generations

Question 5

does selective sweep give a prospective or retrospective view of the genome?

Answer 5

RETROSPECTIVE –> can look where there is low allelic diversity at a specific nt to see where selective sweep occurred in past generations

Question 6

differences btwn complex and simple traits

Answer 6

complex traits are affected by many genes and environmental effects and phenotypes are more continuous

simple traits are affected by 1 or 2 traits and phenotypes are more discrete (1 or the other)

Question 7

what is a threshold trait?

Answer 7

there is a threshold of environment and genetic factors –> beyond this, individuals will show the trait

Question 8

what is variance?

Answer 8

how far each value in a data set is from the mean

Question 9

is variance higher or lower if values are closer and tighter at the mean?

Answer 9

lower

Question 10

what is phenotypic variance?

Answer 10

how much of variance is due to difference in environment AND how much is due to genetic differences

Question 11

what happens to the shape of a phenotype curve if the number of genes increases?

Answer 11

maintains bell curve shape

Question 12

what happens to the shape of a phenotype curve if the number of environmental factors increases?

Answer 12

maintains bell curve shape

Question 13

describe variation in inbred parental line

Answer 13

variation is due to environment only –> Vx = Ve

no genetic variation

Question 14

describe variation in F1 generation

Answer 14

variation is due to environment only –> Vx = Ve

no genetic variation

Question 15

describe variation in F2 generation

Answer 15

variation is due to genotype AND environment –> Vx = Ve + Vg

Question 16

why is there genetic variation in F2 generation?

Answer 16

segregation occurs that increases variance

Question 17

what is broad sense heritability?

Answer 17

proportion of phenotypic variance due to genetic differences

Question 18

equation of broad-sense heritability

Answer 18

H2 = Vg/Vx

Question 19

what is GWAS?

Answer 19

looks at association btwn SNPs and disease to find disease-causing genes close to the SNPs

Question 20

what is a manhattan plot?

Answer 20

shows dots that represent a SNP

Question 21

what does it mean for a manhattan plot to have dots higher up?

Answer 21

there is LOW probability of association btwn disease and SNP occurring by chance alone –> therefore, SNP associated with disease

Question 22

why do we study twins separated at birth?

Answer 22

we don’t have inbred lines for humans, so to measure heritability in humans we can look at identical twins who were separated at birth –> i.e. same genes but diff environment –> can see the role of environment