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Flashcards in Extensions of Mendelian Genetics Deck (65):
1

Most genes have greater than 2 alleles in a population

Multiple Alleles

2

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

2

3

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

Mutation

4

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

T

5

Calculating the number of possible genotypes in a population

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

6

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

4(4+1)/2 = 10

7

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

-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.

8

Phenotype of heterozygote is intermediate to the homozygotes.

Incomplete Dominance

9

Molecular explanation of incomplete dominance

-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

10

One dose of gene product supports life
-Threshold effect
-Trait classified as recessive autosomal

Haplosufficency

11

One dose of gene product is not enough to support life

Haploinsufficency

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-Homozygous wild type= healthy

Haplosufficency/Haploinsufficency

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-Homozygous mutant = unhealthy

Haplosufficency/Haploinsufficency

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-Heterozygous = healthy

Haplosufficency

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-Heterozygous = dead/severely sick

Haploinsufficency

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Example of Haplosufficiency: Cystinosis

-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

17

Example of Haploinsufficiency: BRCA mutations

-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

18

Back up genes

Complementary genes

19

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

Essential gene

20

Presence results in death of individual

Lethal Allele

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Need 2 copies of lethal allele to exhibit lethal phenotype
-most truly lethal in utero
examply: cystic fibrosis

Recessive lethal

22

Recessive lethal in C1 transport due to loss of fxn mutation

cystic fibrosis

23

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

Dominant lethal

24

Caused by a dominant negative mutation

Huntingtons disease

25

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

Dominant Negative Mutation

26

Mutate so it's always on.

Onco gene

27

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

Codominance

28

Molecular explanation of Codominance

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

29

Example of Codominance:

Coat color in some breeds of cattle
-RR= red hairs
-WW= white hairs
-RW= Roan (red and white hairs)

30

One gene is responsible for multiple phenotypes
ex. PKU (phenylketouria)

Pliotropy

31

Autosomal recessive; caused by loss of fxn mutation
-low IQ, seizures, light skin pigmentation (disease will change amino acid for melanin).

PKU (Phenylketouria)

32

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

Linked alleles

33

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

Genetic hitchhiking or Selective sweeps
ex. Crohn's disease

34

Caused by delierious allele
-very close to other genes that give people an advantage.

Crohn's disease

35

One trait is controlled by many gene pairs working together.
ex. eye color, skin color, height, personality, etc...

Polygenic trait

36

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

Epistasis

37

Gene doing the masking

epistatic gene

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gene being masked

hypostatic gene

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Alters the expression of a second gene.
ex. variable cystic fibrosis disease progression

Modifier gene

40

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

Recessive epistasis

41

Example of recessive epistasis:

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

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

Dominant epistasis

43

Example of dominant epistasis:

Summer squash color
-W white: pigment breaks down green pigments
-Y yellow: functioning by not phenotypically expressed
-y green

44

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

Synthetic lethal-negative epistasis

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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

Synthetic Lethal-negative epistasis

46

Not all individuals with a particular genotype display the expected phenotype

Gene expression and the enviornment:
-Genetics cannot be separated from the enviornment

47

Age, internal signals, genetic factors, etc..

Internal enviornment

48

Temperature, chemicals, nurture, etc..

External enviornment

49

Things the environment has an effect on:

-Lung capacity
-Skin color
-IQ
-Metabolism

50

Enzymes lose catalytic function at higher temperature:
ex. siamese cats and Himalayan rabbits have darker fur on cooler areas of body (tail, nose, ears)

Example of environmental effects: temp sensitive genes

51

Variations in phenotype

1. Norm of reaction
2.Penetrance
3. Expressivity

52

Range of potential phenotypes for a particular genotype

Norm of reaction

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

Penetrance

54

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

Expressivity

55

Variations in phenotype due to:

Enviornment, epigenetics, modifier genes

56

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

Position effect (Epigenetics)

57

Can suppress or enhance phenotypic expression

modifier genes

58

Neural growth is over activated

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

Variable expressivity

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

DNA found in mitochondria and chloroplasts:
-Circular
-mtDNA --encode proteins involved in energy
-CpDNA (chloroplast DNA) encode proteins involved in energy production

Extranuclear Genes

61

Mitochondria in egg cytoplasm are inherited in that offspring

Extranuclear inheritnace---typically maternal inheritance

62

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

Maternal Effect

63

Example of Maternal effect

Snail Shell coiling:
-genes expressed in egg influence genotype during development
*Look at mother's genotype, not phenotype!

64

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

b. complete dominance

65

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

b. there is a lethal allele