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Cell Biology II > Chapter 4: Gene interaction > Flashcards

Chapter 4: Gene interaction Flashcards

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1
Q

What is a haplosufficient gene?

A
  • half the amount of protein is sufficient to produce wild-type phenotypes
  • causes simple (complete) dominance
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2
Q

Describe a haploinsufficient gene?

A

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

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3
Q

what are the two ways a gene may be haploinsufficient?

A

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

2) Incomplete dominance

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4
Q

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

A

Null/amorphic mutation

leaky/hypomorphic mutation

Dominant negative mutation

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5
Q

Describe loss of function: Null/amorphic mutation

A
  • produce no functional product
  • homozygous null organisms have mutant (amorphic) phenotype due to gene product absense….
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6
Q

Describe loss of function: Leaky/hypomorphic mutation

A
  • still loss of function
    -produce a SMALL amount of wilf-type gene product
    -homozygous organisms have a mutant (hypomorphic) phenotype
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7
Q

Describe the example of rabbit fur coloration.

A

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)

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8
Q

Describe loss of function: dominant negative mutation

A

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

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9
Q

What are the two examples of gain of function?

A

hypermorphic mutation
neomorphic mutation

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10
Q

describe gain of function: hypermorphic mutation

A

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

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11
Q

Describe the yellow mice phenomenon

A

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…

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12
Q

Describe gain of function: neomorphic mutation

A

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

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13
Q

Describe incomplete dominance

A

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

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14
Q

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

A

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

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15
Q

What is an allelic series?

A

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

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16
Q

What is an essential gene?

A

A gene that results in death if it is mutated

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17
Q

What is a lethal allele?

A

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

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

18
Q

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

A

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

19
Q

Describe the recessive lethal allele in yellow mice?

A

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

20
Q

Lethal ratio?

A

2:1
(yellow to agouti)

21
Q

What are sex-limited traits?

A

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

22
Q

What are sex-influenced traits?

A

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

23
Q

What is penetrance?

A

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(???)

24
Q

What is expressivity?

A

DEGREE to which a genotype is phenotypically expressed in an INDIVIDUAL

25
Q

Compare complete penetrance with incomplete?

A

complete - identical known genotypes yield 100% expected phenotype

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

26
Q

Compare constant expressivity with variable expressivity?

A

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

27
Q

What is incomplete penetrance with variable expressivity?

A

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

28
Q

What is environmental influence on a gene?

A
  • environment can affect how gene is expressed
    diet (PKU)
    temperature (temperature sensitive enzymes)
    nutritional status (grow taller/bettter health)
29
Q

What is pleiotropy?

A

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

30
Q

How do genes “interact” in anabolic and catabolic pathways?

A

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

31
Q

Describe the one-gene-one-enzyme hypothesis?

A

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

32
Q

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

A
  • 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
33
Q

what is epistasis

A

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

34
Q

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

A

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

35
Q

Describe complementary gene interaction

A
  • 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)

36
Q

Describe duplicate gene action

A
  • 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)

37
Q

Describe dominant gene interaction

A

-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)

38
Q

Describe recessive epistasis

A

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

39
Q

Describe dominant epistasis

A

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

40
Q

Describe dominant supression

A
  • occurs when dominant allele of one gene suppresses the expression of alleles of a second gene

ex: blue pimpernel flower color

41
Q

Describe how complementation occurs

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

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