Chapter 4: Gene interaction

Question 1

What is a haplosufficient gene?

Answer 1

• half the amount of protein is sufficient to produce wild-type phenotypes
• causes simple (complete) dominance

Question 2

Describe a haploinsufficient gene?

Answer 2

Half the amount of protein is NOT sufficient to produce wild-type phenotype

Question 3

what are the two ways a gene may be haploinsufficient?

Answer 3

1) Mutant allele is dominant (Huntingtons) (1/2 of protein produces disease)

2) Incomplete dominance

Question 4

What are the three “loss of function” effects of a mutation

Answer 4

Null/amorphic mutation

leaky/hypomorphic mutation

Dominant negative mutation

Question 5

Describe loss of function: Null/amorphic mutation

Answer 5

• produce no functional product
• homozygous null organisms have mutant (amorphic) phenotype due to gene product absense….

Question 6

Describe loss of function: Leaky/hypomorphic mutation

Answer 6

• still loss of function
  -produce a SMALL amount of wilf-type gene product
  -homozygous organisms have a mutant (hypomorphic) phenotype

Question 7

Describe the example of rabbit fur coloration.

Answer 7

Full color (CC C-) = wild type… homo/hetero for C allele

Chinchilla = hypomorphic/leaky

Himalayan = hypomorphic temperature sensitive.. enzyme that produces pigment is temperature sensitive, only functions in extremeties where there is less heat… inactibe at body temp

Albino = Null (amorphic)

Question 8

Describe loss of function: dominant negative mutation

Answer 8

messes up whole protein, have effect on 3rd gene

Products interact abnormally with protein products of another gene (3rd gene), leading to messed up proteins

Question 9

What are the two examples of gain of function?

Answer 9

hypermorphic mutation
neomorphic mutation

Question 10

describe gain of function: hypermorphic mutation

Answer 10

Makes more protein that you should (ex: promotor mutation)

excessive expression of the gene product… excessive gene action
mutant may be severe/lethal in the homozygous genotype than in the heterozygous genotype

Question 11

Describe the yellow mice phenomenon

Answer 11

examples of gain of function: hypermorphic
wild type carries the yaly promotor, raly gene, agouti promotor and agouti gene….
mutant deletes many of these, left with raly promotor and agouti gene… the agouti gene is expressed more…. more yellow pigment…

Question 12

Describe gain of function: neomorphic mutation

Answer 12

mutant allele has novel function that produces a mutant phenotype in homozygous and heterozygous organisms
- may be more severe in homozygous organisms

Question 13

Describe incomplete dominance

Answer 13

heterozygote creates an intermediate phenotype
-identical genotypic and phenotypic ratios (neither is dom or recessive)

Question 14

What were the blood types response to anti-A or anti-B, and what are their possible genotypes?

Answer 14

Type A) anti-a = clumping… anti-b=no clumping.. IAIA or IAi

type B) anti-a = no clumping… anti-b=clumping.. IBIB or IBi

type AB) anti-a=clumping…anti-b=clumping… IAIB

type O) anti-a=no clumping… anti-b= no clumping… ii

Question 15

What is an allelic series?

Answer 15

A>B>C>D>E etc… multiple alleles, dominance relationships…

Question 16

What is an essential gene?

Answer 16

A gene that results in death if it is mutated

Question 17

What is a lethal allele?

Answer 17

Dominant lethal…
- both homozygotes and heterozygotes express lethal phenotype
-ex: huntington’s disease

recessive lethal..
- only homozygotes express lethal phenotype
-ex: yellow mice

Question 18

What affect does delayed age of onset have on a population?

Answer 18

allows dominant lethal allele to persist in the population…
ex: not knowing you have huntington’s until you’re in your 30s/50s

Question 19

Describe the recessive lethal allele in yellow mice?

Answer 19

Wild type- carry Raly gene which is essential for mouse embryonic development (and moderate levels of yellow pigment)

Mutant- no Raly protein, causes issues with embryonic development …

(AA) = agouti
AAy= yellow
AyAy= lethal

Question 20

Lethal ratio?

Answer 20

2:1
(yellow to agouti)

Question 21

What are sex-limited traits?

Answer 21

-expression of trait is limited to one sex
—- same genotype…
—-ex: only male canaries can sing and only female mammals can lactate

Question 22

What are sex-influenced traits?

Answer 22

-phenotype differs depending on the sex of the organism…
-same genotype…

Question 23

What is penetrance?

Answer 23

FREQUENCY with which a dominant or homozygoues recessive phenotype manifests itself in individuals of a POPULATION

freq= # of individuals in population with the same genotype(???)

Question 24

What is expressivity?

Answer 24

DEGREE to which a genotype is phenotypically expressed in an INDIVIDUAL

Question 25

Compare complete penetrance with incomplete?

Answer 25

complete - identical known genotypes yield 100% expected phenotype incomplete - identical known genotypes yield , less than 100% expected phenotype

Question 26

Compare constant expressivity with variable expressivity?

Answer 26

constant - identical known genotypes with no expressivity effect yield 100% expected phenotype Variable - identical known genotypes with an expressivity effect yield a range of phenotypes

Question 27

What is incomplete penetrance with variable expressivity?

Answer 27

Identical known genotypes produce a broad range of phenotypes, due to varying degrees of gene activation and expression

Question 28

What is environmental influence on a gene?

Answer 28

- environment can affect how gene is expressed diet (PKU) temperature (temperature sensitive enzymes) nutritional status (grow taller/bettter health)

Question 29

What is pleiotropy?

Answer 29

one gene/mutation affects a variety of phenotypes ex: sickle cell, folding of protein causes sickling of blood cells, which affects many other phenotypes

Question 30

How do genes "interact" in anabolic and catabolic pathways?

Answer 30

Anabolic - sequencial action of gene products catalyzes steps of a biosynthesis... each step is catalyzed by a different gene Catabolic - action of gene products breaks down complex compounds into simpler compounds

Question 31

Describe the one-gene-one-enzyme hypothesis?

Answer 31

proposed by George Wells Beadle in the US, is the theory that each gene directly produces a single enzyme, which consequently affects an individual step in a metabolic pathway. gene--- produces enzyme--- enzyme affects steps in metabolic pathways

Question 32

Describe how the one-gene-one-enzyme hypothesis was tested?

Answer 32

- orange bread mold 1- exposed mold growing on minimal medium to UV radiation to cause small mutations 2-transferred irradiated conidia to complete medium, phototrophs(wild) and auxotrophs(mutant) grow 3 -transferred growing fingi back to minimal medium, phototrophs grow but auxotrophs do not 4- transferred auxotrophs to different supplemented minimal media and controls (+amino acids, vitamins, nucleic acids) growth in amino acid supplement 5- added a different amino acid to every vile, growth in methionine

Question 33

what is epistasis

Answer 33

allele of one gene modifies or prevents the expression of alleles of anotyher gene - modification of 9:3:3:1 ratio - law of independent assortment

Question 34

What are the 6 types of epistatic gene interactions and what are their ratios?

Answer 34

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 35

Describe complementary gene interaction

Answer 35

- occurs when genes must act in tandem to produce a phenotype - wild type action from both genes is REQUIRED to product the wild type - mutation of one or both produces a mutant (ex: sweet pea flower color)

Question 36

Describe duplicate gene action

Answer 36

- allows dominant alleles of either duplicate gene to produce the wild type - only organisms with homozygous mutations of both genes have a mutant -(dom allele at either locus allows for wild type) (ex: bean flower color)

Question 37

Describe dominant gene interaction

Answer 37

-occurs between genes that each contribute to a phenotype -produces ONE phenotype if dominant alleles are present at each gene, - produces TWO if recessive alleles are homozygous for either gene - produces THREE if recessive homozygosity occurs at both genes (squash example)

Question 38

Describe recessive epistasis

Answer 38

recessive epistasis occurs when recessive alleles at one gene mask or reduce the expression of alleles at the interacting locus - ex: labrador retriever coat color

Question 39

Describe dominant epistasis

Answer 39

-a dominant allele of one gene masks or reduces expression of alleles of a second gene ex: summer squash color

Question 40

Describe dominant supression

Answer 40

- occurs when dominant allele of one gene suppresses the expression of alleles of a second gene ex: blue pimpernel flower color

Question 41

Describe how complementation occurs

Answer 41

- mutation in two separate genes are crossed, restores to wild type