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Bio 233 > Extensions of Mendelian Genetics > Flashcards

Extensions of Mendelian Genetics Flashcards

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1
Q

Most genes have greater than 2 alleles in a population

A

Multiple Alleles

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2
Q

A single diploid can have up to _____ alleles in its genome.

A

2

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3
Q

Alleles arise through changes in the DNA sequence in a gene by________.

A

Mutation

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4
Q

T or F: Wild type occurs most often, but does not have to be dominant.

A

T

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5
Q

Calculating the number of possible genotypes in a population

A

-Based on number of alleles
n=number of alleles
Possible genotypes=n(n+1)/2

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6
Q

If there are 4 possible alleles, the number of genotypes in the population is?

A

4(4+1)/2 = 10

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7
Q

Hierarchy of dominance: Fly example
w^+ = wildtype (red)
w^e = eosin (reddish orange)
w = white allele

A
  • Decreasing dominance
  • fly eye color gene has more than 3 alleles
  • has to do with gene expression and gene product function in depositing the color in the eyes.
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8
Q

Phenotype of heterozygote is intermediate to the homozygotes.

A

Incomplete Dominance

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9
Q

Molecular explanation of incomplete dominance

A
  • Dependent upon gene dosage
  • Homozygosity for functional allele causes 2 “doses” of a gene product
  • Heterozygosity causes one “dose” of gene product
  • Homozygosity for nonfunctional allele causes no dose of gene product
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10
Q

One dose of gene product supports life

  • Threshold effect
  • Trait classified as recessive autosomal
A

Haplosufficency

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11
Q

One dose of gene product is not enough to support life

A

Haploinsufficency

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12
Q

-Homozygous wild type= healthy

A

Haplosufficency/Haploinsufficency

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13
Q

-Homozygous mutant = unhealthy

A

Haplosufficency/Haploinsufficency

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14
Q

-Heterozygous = healthy

A

Haplosufficency

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15
Q

-Heterozygous = dead/severely sick

A

Haploinsufficency

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16
Q

Example of Haplosufficiency: Cystinosis

A
  • is an autosomal recessive disorder
  • caused by loss of fxn mutations in the CTNS gene
  • Causes cells to store cystine
  • patients have 100x more cystine than noncarrier controls
  • carriers (patients) have 6-10x more cystine
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17
Q

Example of Haploinsufficiency: BRCA mutations

A
  • autosomal dominant
  • mutations cause increased risk for breast cancer
  • gene products are involved in DNA repair
  • Loss of fxn mutations increase risk for breast cancer
  • heterozygosity causes increased risk of breast cancer
  • individual that is homozygous for the mutation is embryonic lethal
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18
Q

Back up genes

A

Complementary genes

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19
Q

A gene that encodes a product required for life; when mutated, causes a lethal phenotype
-no back up gene

A

Essential gene

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20
Q

Presence results in death of individual

A

Lethal Allele

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21
Q

Need 2 copies of lethal allele to exhibit lethal phenotype

  • most truly lethal in utero
    examply: cystic fibrosis
A

Recessive lethal

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22
Q

Recessive lethal in C1 transport due to loss of fxn mutation

A

cystic fibrosis

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23
Q

both homozygotes for lethal allele and heterozygotes display the lethal phenotype

  • typically from:
    1) gain of fxn mutation
    2) dominant negative mutation
    ex. Huntingtons disease
A

Dominant lethal

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24
Q

Caused by a dominant negative mutation

A

Huntingtons disease

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25
Q

Loss of fxn mutation in mutant allele interferes with fxn of wild type allele

A

Dominant Negative Mutation

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26
Q

Mutate so it’s always on.

A

Onco gene

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27
Q

Heterozygote shows the phenotypes of both homozygotes simultaneously.
-ex: AB blood type

A

Codominance

28
Q

Molecular explanation of Codominance

A

Equally strong, expressed gene products that don’t interfere with the cellular functions of each other.

29
Q

Example of Codominance:

A

Coat color in some breeds of cattle

  • RR= red hairs
  • WW= white hairs
  • RW= Roan (red and white hairs)
30
Q

One gene is responsible for multiple phenotypes

ex. PKU (phenylketouria)

A

Pliotropy

31
Q

Autosomal recessive; caused by loss of fxn mutation

-low IQ, seizures, light skin pigmentation (disease will change amino acid for melanin).

A

PKU (Phenylketouria)

32
Q

When alleles are on the same chromosome, they tend to be inherited together unless separated by recombination.

A

Linked alleles

33
Q

When 2 or more genes show strong linkage and one of the 2 genes has an allele that give a selective advantage, the other allele tends to be inherited with the advantagous allele

A

Genetic hitchhiking or Selective sweeps

ex. Crohn’s disease

34
Q

Caused by delierious allele

-very close to other genes that give people an advantage.

A

Crohn’s disease

35
Q

One trait is controlled by many gene pairs working together.

ex. eye color, skin color, height, personality, etc…

A

Polygenic trait

36
Q

Form of gene interaction in which one gene interferes with the expression of another gene.

  • polygenic phenomena
  • one locus interferes with another locus
  • one gene masks another gene
A

Epistasis

37
Q

Gene doing the masking

A

epistatic gene

38
Q

gene being masked

A

hypostatic gene

39
Q

Alters the expression of a second gene.

ex. variable cystic fibrosis disease progression

A

Modifier gene

40
Q

Homozygous recessive genotype at locus A masks phenotypic expression at locus B

  • aa epistatic to BB, Bb, or bb.
  • aaB_ and aabb have same phenotype
A

Recessive epistasis

41
Q

Example of recessive epistasis:

A

Coat color in mice

  • A_ agouti
  • aa black
  • C_ pigment made and deposited
  • cc no pigment made and deposited
    9: 3:4 phenotypic ratio
42
Q

Presence of dominant allele at locus A masks phenotypic expression at locus B

  • A_ is epistatic to BB, Bb, or bb
  • A_B_ and A_bb will have same phenotypic outcome
A

Dominant epistasis

43
Q

Example of dominant epistasis:

A

Summer squash color

  • W white: pigment breaks down green pigments
  • Y yellow: functioning by not phenotypically expressed
  • y green
44
Q

Wild type gene products are involved in complementary pathways.
ex. DNA repair enzymes, transcription factors, etc…

A

Synthetic lethal-negative epistasis

45
Q 
Mutation A- alive
Mutation B- alive
Mutation in both A and B- dead
*A is masking mutation in b
B is masking mutation in a
A

Synthetic Lethal-negative epistasis

46
Q

Not all individuals with a particular genotype display the expected phenotype

A

Gene expression and the enviornment:

-Genetics cannot be separated from the enviornment

47
Q

Age, internal signals, genetic factors, etc..

A

Internal enviornment

48
Q

Temperature, chemicals, nurture, etc..

A

External enviornment

49
Q

Things the environment has an effect on:

A
  • Lung capacity
  • Skin color
  • IQ
  • Metabolism
50
Q

Enzymes lose catalytic function at higher temperature:

ex. siamese cats and Himalayan rabbits have darker fur on cooler areas of body (tail, nose, ears)

A

Example of environmental effects: temp sensitive genes

51
Q

Variations in phenotype

A
  1. Norm of reaction
  2. Penetrance
  3. Expressivity
52
Q

Range of potential phenotypes for a particular genotype

A

Norm of reaction

53
Q

The percentage of individuals with a particular genotype of interest who show the expected phenotype

A

Penetrance

54
Q

Degree to which a phenotype is expressed; severity of the phenotype

A

Expressivity

55
Q

Variations in phenotype due to:

A

Enviornment, epigenetics, modifier genes

56
Q

Physical location of a gene that can influence expression; genetic background of the individual
*nearby CpG island?

A

Position effect (Epigenetics)

57
Q

Can suppress or enhance phenotypic expression

A

modifier genes

58
Q

Neural growth is over activated

A

Incomplete penetrance (50-80% penetrance)

ex. Neurofibromatosis: human disease caused by dominant allele, not caused by gene dosage
- expressivity ranges from brown spotting to tumor like growths

59
Q

Variable expressivity

A

Ex. Osteogenesis imperfecta (brittle bone disease)

  • autosomal dominant
  • 100% penetrance
  • may have one or up to three of the following traits: blueness in sclerae of eyes, fragile bones, deafness
60
Q

DNA found in mitochondria and chloroplasts:

  • Circular
  • mtDNA –encode proteins involved in energy
  • CpDNA (chloroplast DNA) encode proteins involved in energy production
A

Extranuclear Genes

61
Q

Mitochondria in egg cytoplasm are inherited in that offspring

A

Extranuclear inheritnace—typically maternal inheritance

62
Q

Phenotype of offspring is determined by nuclear genotype of the mother
-mRNA and proteins are made in oocyte and deposited there before fertilization.

A

Maternal Effect

63
Q

Example of Maternal effect

A

Snail Shell coiling:

  • genes expressed in egg influence genotype during development
  • Look at mother’s genotype, not phenotype!
64
Q

In a plant species, two blue plants are mated and produce 303 blue plants and 98 white plants. These observations can best be explained by:

a. incomplete dominance
b. complete dominance
c. codominance
d. haploinsufficiency

A

b. complete dominance

65
Q

A cross between two short-tailed mice results in offspring in the ratio of 67 short-tailed and 34 long-tailed. The best explaination for this result is that:

a. two alleles are codominant
b. there is a lethal allele
c. there are at least three alleles
d. there is simple dominance between two alleles

A

b. there is a lethal allele

Bio 233 (20 decks)

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