week 3 (gene interaction)

Question 1

define: wildtype vs mutant

Answer 1

• wildtype = most common allele in natural populations
  ⤷ does not mean dominant
• mutant = not wildtype

Question 2

name + explain: functional effects of mutations (4)

Answer 2

• wildtype = prod. functional prot.

1. loss of function (null mut.)
⤷ null allele produces no protein
⤷ homo = none, hetero = 1 copy

2. leaky allele
⤷ prod. less prot. or prot w/ diminished function

3. gain of function
⤷ hypermorphic: prod. more than wildtype
⤷ neomorphic: prod. prod. w/ new functions

4. loss of function (dom negative mut.)
⤷ result of impaired interactions between 2 genes
⤷ mut. at one gene can alter pep. prod. -> incorrect interation with second gene

Question 3

define: incomplete dominance

Answer 3

• dominance may not completely mask recessive
• results in blended phenotype
  ⤷ if het.

Question 4

define: allelic series

Answer 4

• result of hierarchy of dominance across multiple alleles
  ex. bunny colour
  ⤷ full colour > chinchilla > himalayan > albino
  ⤷ wildtype > leaky (hypomorphic) > hypomorphic > null

Question 5

define: codominance

Answer 5

• not blended but a unique phenotype
• ex. blood types
  ⤷ AB doesn’t have AB antigens (blend), has both A and B (new phenotype)

Question 6

define: lethal alleles

Answer 6

• single gene mut. that result in death or org.
• often recessive
  ⤷ so het. can be carriers
• ex. agouti mice
  ⤷ wildtype = mix of black and yellow (agouti)
  ⤷ mut. = yellow (het. AA^Y)
  ⤷ mut. w/ 2 A^Y genes die
  ⤷ A^Y dom. mut.

Question 7

define: sex limited trait

Answer 7

• pheno. only expression in one sex

Question 8

define: sex influenced traits

Answer 8

• both sexes carry gene but pheno. varies
• ex. in goats
  ⤷ B1B2 = bearded in males but not females
  ⤷ B2B2 = bearded for males and females

Question 9

define: penetrant, nonpenetrant, fully penetrant, incomplete penetrance

Answer 9

• penetrant: pheno. matches geno.
• nonpenetrant: indiv. w/ geno. does not prod. assoc. pheno.
• fully penetrant: geno. always expresses assoc. pheno.
• incomplete penetrance: traits that are nonpenetrant in some but penetrant in others
  ⤷ ex. polydactyly

Question 10

define: variable expressivity

Answer 10

• like incomplete penetrance but pheno. are variable instead of absent/present
• diff. combinations of symptoms
  ⤷ ex. Waardenburg syndrome

Question 11

define: gene-envrt. interaction (w/ example)

Answer 11

• influence of envrt. on gene expression adn pheno.
• ex. PKU
  ⤷ autosomal rec.
  ⤷ absence of enz. that breaks down phenylalanine
  ⤷ overtime PKU builds up -> toxicity
  ⤷ solution: restrict phenylalanine in diet

Question 12

define: pleiotropy

Answer 12

• one gene affects many pheno.
• ex. juvenile hormone in flies
  ⤷ impacts dev. time, body size, life span
• ex. sickle cell anemia
  ⤷ many symptoms

Question 13

define: epistasis

Answer 13

• effect on 1 gene is dep. on alleles of other genes

Question 14

name: types of epistasis and their ratios (6)

Answer 14

1. complementary gene interaction 9:7
2. duplicate gene action 15:1
3. dominant gene interaction 9:6:1
4. recessive epistasis 9:3:4
5. dominant epistasis 12:3:1
6. dominant suppression 13:3

Question 15

explain: complementary gene interaction (1.)

Answer 15

• 9:7
• genes must act in tandem to prod. a pheno.
• ex. sweet peas
  ⤷ need precursor I and II to have any pigment

Question 16

explain: duplicate gene action (2.)

Answer 16

• 15:1
• allows dom. alleles of either gene to prod. wildtype
• ex. bean flowers
  ⤷ need homo. mut. to show mutant
  ⤷ any dom. allele expresses it’s dom. pheno.

Question 17

explain: dominant gene interaction (3.)

Answer 17

• 9:6:3
• 3 diff. pheno.
  ⤷ 9dom. both genes
  ⤷ 6 homo. rec. one gene (at least)
  ⤷ 3 both homo. rec.
• ex. squash shape

Question 18

explain: recessive epistasis (4.)

Answer 18

• 9:3:4
• homo. rec. for one gene masks dom. alleles for the other gene
• ex. labrador colours
  ⤷ homo. reccesive for no colour deposition overrides any dom. colour allele

Question 19

explain: dominant epistasis (5.)

Answer 19

• 12:3:1
• dominant allele masks expression of other gene
• ex. summer squash colour
  ⤷ dominant white allele blocks other colours

Question 20

explain: dominant suppression (6.)

Answer 20

• 13:3
• dominant masks expression of other gene in inhibitory manner
• ex. pimpernel flower colour
  ⤷ dominant precursor suppresses other gene (colour) -> white flower

Question 21

summarize: violations to mendel’s laws

Answer 21

• incomplete/partial dominance
• co dominance
• allelic series
• lethal alleles
• sex-limited and sex-influenced traits
• epistasis

Question 22

define: genetic dissection

Answer 22

• identifying steps of a genetic pathway
• ex. neurospora methionine experiment (horowitz)
  ⤷ used minimal medium w/ diff. mutants to see if things grew
  ⤷ used complementation analysis (big chart w/ + and - for IDing mut.)