Heritability

Question 1

what does heritability measure

Answer 1

• proportion of the total phenotypic variance among indviduals in a population that is due to differences in their genes

Question 2

what is the range of heritability? (3)

Answer 2

• it ranges from 0-1
• 0.0 = all differences are due to environment
• 1.0 = all differences are due to genes

Question 3

parent-offspring regression

Answer 3

• graph of the parent phenotype with the offspring phenotype

Question 4

• slope of regression (2)

Answer 4

• slope measures extent to which offspring resemble their parents
• essentially heritability

Question 5

parent-offspring regression

- slope = 0 (2)

Answer 5

• no resemblance

- no response to selection, evolution cannot happen

Question 6

parent-offspring regression

- slope = 1.0 (2)

Answer 6

• strong resemblance

- strong response to selection, evolution can happen

Question 7

what is the formula for heritability (by looking at response to selection)

Answer 7

• heritability = R/S

Question 8

what is S in the formula for heritability (by looking at response to selection) (2)

Answer 8

• selection differential

- s = Xs - Xp

Question 9

what is R in the formula for heritability (by looking at response to selection) (2)

Answer 9

• response to selection

- R = Xr - Xp

Question 10

Xs

Answer 10

• mean of the surviving individuals after selection event

Question 11

Xp

Answer 11

• mean of original population

Question 12

Xr

Answer 12

• mean of new generation after selection

Question 13

R = S

Answer 13

• heritability = 1

Question 14

R < S

Answer 14

• heritability < 1

Question 15

R > S

Answer 15

• S is not smaller than R in populations

Question 16

H = 0 (2)

Answer 16

• does not mean that a trait does not have genetic basis

- if all individuals have the same genotype, there will be no variability at that locus even tho there is genetic basis

Question 17

variability in selfed-lines (identical genotype) (2)

Answer 17

• Vphenotype = Venvironment

- H = 0

Question 18

variability in selfed-lines (identical genotype) (2)

Answer 18

Vphenotype = Vgenotype - Venvironment

- H > 0

Question 19

H > 0 (2)

Answer 19

• does not mean that differences among populations are genetic
• individuals that are genetically identical may show variability in different environmental conditions

Question 20

• why may there be differences in heritability estimates? (2)

Answer 20

• may be due entirely to environmental differences
• genetically identical heterogenous populations raised with maximal conditions will show greater H, but those grown in the more heterogenous environment will have low H

Question 21

what are heritability estimates valid for?

Answer 21

• only valid for the population (and the time and place) from which they were obtained

Question 22

phenylketonuria (3)

Answer 22

• genetic recessive disorder
• deficient in enzyme that converts phenylalanine into tyrosine
• if untreated, may develop severe mental retardation

Question 23

how does environment and heritability affect those with phenylketonuria (2)

Answer 23

• trait has clear genetic basis so heritability should be high, but it is not because it can be controlled by environment
• homozygous individuals who eat low phenylalanine diet and high tyrosine show no symptoms

Question 24

what are heritability estimastes good for?

Answer 24

• allows us to predict whether a population will respond to artificial or natural selection