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Exam 2 Flashcards

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1
Q

Mendels Law of Segregation

A

2 alleles of each gene separate/segregate during gamete formation, and then unite at random (1 from each parent) at fertilization

  • MI separates homologs; then MII separates sisters. Each gamete ends up with 1 copy of each allele
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2
Q

What happens in meiosis that underlies law of segregation?

A

Homologous chromosomes align in metaphase I and segregate into separate daughter cells

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3
Q

Mendel’s Law of Independent Assortment

A

During gamete formation, different pairs of alleles segregate independently of each other

50% chance of receiving alleles from mother vs father

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4
Q

what happens in meiosis that underlies law of IA?

A

Homologous chromosomes align in MetaphaseI with independent orientation; the orientation of 1 tetrad does not influence the orientation of another

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5
Q

independent assortment on same vs different chromosomes

A
  • alleles on different chromosomes = always independently assort
  • alleles on the same chromosome may/may not independently assort
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6
Q

independent assortment on the same chromosomes

A

2 alleles on the same chromosome will assort into the same gamete unless crossing over swaps one onto the homologous chromosomes

therefore, IA on the same chromosome may or may not occur

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7
Q

test cross

A

cross recessive genotype with mystery genotype

  • all dominant –> homozygote dom
  • half dominant –> heterozygote dom
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8
Q

why do a test cross?

A

figure out the genotype of an individual

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9
Q

true-breeding/pure-breeding

A

homozygous individuals whose line produces the same phenotype when selfed 100% of the time

**can assume genotype is homozygous

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10
Q

how to figure out which is the dominant individual?

A

look at heterozygous
-cross 2 pure-breeding individuals to get all heterozygous F1 generation and analyze the phenotypes

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11
Q

monohybrid self cross

A

heterozygotes of 1 gene crossed with each other

Ex/ Aa x Aa

1:2:1 genotypic ratio
3:1 phenotypic ratio

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12
Q

/

A

alleles on different homologs of the same chromosomes
Ex/ A/a

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13
Q

;

A

alles on different chromosomes
Ex/ A/a;B/b

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14
Q

dihybrid test cross

A

2 genes controlling 2 traits
-heterozygotes crossed with recessive homozygotes
Ex/ A/a;B/b x a/a;b/b

genotypic: 1:1:1:1
phenotypic: 1:1:1:1

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15
Q

dihybrid self cross

A

selfing of dihybrid

genotypic: 9:3:3:1
phenotypic: 9:3:3:1

9 - both dom
3 - 1 dom; 1 rec
3 - 1 rec; 1 dom
1 - both rec

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16
Q

product rule

A

AND
- the probability that 2 or more independent events occurring together is the product of the probabilities that each will occur by itself

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17
Q

sum rule

A

OR
- the probabilities of 2 mutually-exclusive events occurring is the sum of their individual probabilities

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18
Q

a scientific hypothesis makes — predictions and is —-.

A

testable and is falsifiable.

*null hypothesis must make a testable prediction.
ex/ IA will occur.

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19
Q

null hypothesis

A

there is no significant difference between the observed and expected frequencies

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20
Q

must be very certain that you can reject the null hypothesis

A

5%

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21
Q

chi-square tests

A

determine p-value using a formula

total = (observed - expected)^2 /expected

compare values in chart

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22
Q

p value

A

represents the probability that the null hypothesis is TRUE

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23
Q

p > 0.05

A

fail to reject the null hypothesis

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24
Q

p < 0.05

A

reject the null hypothesis with 95% certainty
- there is a greater than 95% chance that the null hypothesis is not true

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25
Q

degrees of freedom

A

the number of values observed/expected minus 1

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26
Q

how to find expected values for chi square?

A

look at total and use ratio expected based on the type of cross

ex/ monohybrid self cross = 3:1
out of 400
300 and 100 are expected values

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27
Q

genes controlled by single genes…

A

display characteristic inheritance patterns
*though most traits are not controlled by a single gene

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28
Q

genetic diseases

A
  • typically involve 2 possible alleles: “disease” and “wild-type”
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29
Q

autosomal recessive disorders

A
  1. males and females equally affected
  2. unaffected individuals can have affected children via heterozygous carriers
  3. can skip generations
  4. rare
  5. becomes more common with inbreeding
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30
Q

rareness in diseases stipulation

A

when discussing diseases, you can assume these traits are rare so people entering the pedigree do NOT carry the disease allele
- unless you have info to suggest otherwise

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31
Q

why does disease become more common with inbreeding?

A

may be rare in the general population, but may not be rare in family –> so the homozygote recessive genotype becomes more common

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32
Q

tay-sachs symptoms

A
  • affects babies a few months old
  • lose vision and react abnormally when startled
  • paralysis
  • deafness
  • seizures
  • inability to breath/swallow
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33
Q

tay-sachs causes

A
  • healthy neuron lysosomes act as the waste processing center of the cell
  • With TS, lysosome enzymes cannot properly break down fatty cell products (gangliosides).
  • Products build up and destroy cells
  • recessive autosomal disease
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34
Q

tests for pregancy with genetic counselors

A

carrier test of parents (genotypes)
prenatal/preimplantation tests

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35
Q

PGD

A

Preimplantation Genetic Diagnosis
- blastomere from invitro fertilized embryos are removed and tested for disease gene

  • embryos with disease are discarded/donated to science
  • embryos without are implanted or frozen
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36
Q

autosomal dominant disorders

A
  1. males and females are equally affected
  2. affected individuals always have an affected parent (no heterozygous carriers bc they are affected too)
  3. does not skip generations
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37
Q

huntington’s disease

A

rare, fatal, degenerative neurological disease caused by a dominant disease allele
- start showing symptoms in 40s
- death within 15 years

  • mutation in Huntingtin gene
  • Huntington’s aggregates in neurons, shaking, personality changes
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38
Q

x-linked inheritance rules

A
  1. males inherit Y from their father and MUST inherit X from their mother
  2. females inherit one X from father and one X from mother
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39
Q

x-linked recessive disorders

A
  1. males more frequently affected
  2. never transmitted from fathers to daughters
  3. All sons of affected mothers will also be affected by the trait
  4. can “skip generations” via female carriers
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40
Q

x-linked dominant disorders

A
  1. females more frequently affected
  2. ALL of the daughters and NONE of the sons of affected fathers have the trait
  3. does not “skip generations”
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41
Q

penetrance

A

the percentage of individuals with a particular genotype that demonstate the expected phenotype

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42
Q

complete penetrance

A

100%

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43
Q

incomplete penetrance

A

1-99%

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44
Q

penetrance calculations over or underestimate?

A

overestimate
- there could be other nonpenetrant individuals that we are not certain about
- the demoninator is larger so the overall fraction/percentage will be smaller than originally estimated

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45
Q

variable expressivity

A

for individuals with the same genotype, there is a range of phenotype severity/expression

** the degree with which a genotype is expressed as a phenotype (how much phenotype is shown)

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46
Q

complete dominance

A

the heterozygous phenotype is the same as homozygous dominant

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47
Q

incomplete dominance

A

the heterozygous phenotype is intermediate between the two homozygotes

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48
Q

codominance

A

the heterozygous phenotype is a mizture of the 2 homozygotes
– aspects of both homozygotes are shown

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49
Q

incomplete and codominance

A

the same genotypic but different phenotypic ratios as complete dominance

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50
Q

monomorphic traits

A

have single “wild type” allele

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51
Q

variant alleles

A
  • rare (<1%)
  • classified as mutant
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52
Q

polymorphic traits

A

have multiple common allele variants
- There is no single wild type allele

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53
Q

trait classifications are NOT static

A
  • classifications can change
  • a mutant allele can become a common varient over time or a common varient can be lost from the population
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54
Q

AB blood type

A

The IAIB heterozygotes express two functional varients of the enzyme (Type A and B enzyme)

IAIB

***polymorphic

55
Q

O blood type

A

The i allele encodes a null version of the enzyme (non-functional enzyme)

ii

56
Q

B blood type

A

The IB allele encodes a version of the enzyme that adds B sugars

IBIB
IBi

57
Q

A blood type

A

The IA allele encodes a version of the enzyme that adds A sugars

IAIA
IAi

58
Q

how does red blood cells get their type?

A

Red blood cells have a protein on their cell membranes that can be modified by an enzyme
- enzyme decides phenotype (blood type)

59
Q

with regard to blood type, IA is

A

codominant to IB and dominant to i

60
Q

how to know if 1 or 2 genes are involved?

A

look at ratios

61
Q

pleiotrophic allele

A

affects several properties of an oranis,

62
Q

pleiotrophy in cystic fibrosis

A

single gene defect leads to lung disease, sterility, pancreatic dysfunction

BC the gene product (CFTR protein) has important functions in the cells of the respiratory, digestive, and reproductive tracts

63
Q

dominance relationships are specific to..

A

each phenotype an allele affects

64
Q

lethality and the pelger anomaly

A

recessive for pelger is lethal phenotype

lethal means that they have severe defects or are never born

changes the phenotypic ratios

65
Q

with regard to the nuclear morphology phenotype, the “pelger” allele is…

A

dominant

66
Q

with regard to the lethality phenotype, the “pelger” allele is…

A

recessive

67
Q

when 2 genes impact the same trait…

A

we can observe the same familiar ratios or see modified rations

68
Q

fewer phenotypic classes than expected indicate…

A

epistasis

69
Q

epistasis

A

the effect of one gene masks the effect of another

  • often occurs when 2 genes encode members of the same biochemical pathway
70
Q

bombay phenotype

A

recessive epistasis
hh genotype
- overrides the blood type for an O blood type
- doesn’t matter what parental blood types are
- 2 recessive h alleles mask the IA alleles phenotypic effect

71
Q

epistasis is a…

A

gene-gene interaction (relationship between 2 genes vs 2 alleles of same gene like in dominance relationships)

72
Q

duplicate/redudant genes

A

collapse all phenotypic categories with 1+ dominant allele for either gene
15:1 ratio

73
Q

dihybrid cross ratio

A

9:3:3:1

74
Q

complementary ratio

A

9:7

75
Q

duplicate genes ratio

A

15:1

76
Q

recessive epistatis ratio

A

9:3:4

77
Q

dominant epistatis ratio

A

12:3:1

78
Q

complementation

A

when 2 individuals with the same mutant phenotype but different homozygous recessive genotypes produce offsprng with the wild-type phenotype when crossed

79
Q

complementation test

A

only works for recessive mutants
- always cross homo recessive mutants that are mutant for only one gene

-no complementaion if mutant trait appears (same gene)
- complementation if mutatnt trait does not appear (mutations in different genes)

  • failure to complement with itself bc if has mutant and crosses with itself, the mutant phenotype will remain.
80
Q

melanocytes

A
  • found in skin
  • produce pigmented melanosomes that give skin its color
81
Q

MC1R1/MC1R1

A

can produce different doses of eumelanin vs phenomelanin depending on the available receptor variants

82
Q

purebreeding lines

A

organisms that produce offspring with specific parental traits that remain constant from generation to generation

(often homozygous)

83
Q

dihybrids

A

individual that is heterozygous at 2 different genes

84
Q

parental types

A

phenotypes that reflect a previously existing parental combination of alleles that is retained during gamete formation

85
Q

recombinant types

A

phenotypes reflecting a new combo of alleles that occurred during gamete formation

86
Q

hemizygote

A

genotype for genes present in only one copy in an otherwise 2n organism
ex/ x-linked genes in a male

87
Q

polymorphic

A

describes a locus with 2 or more distinct alleles in a population

88
Q

common variants

A

high-frequency alleles of a polymorphic gene or other chromosomal locus

89
Q

pleiotrophy

A

single gene determines a number of distinct and seemingly unrelated characteristics

90
Q

advantageous vs disadvantageous alleles

A

an allele that is advantageous in one environment may be disadvantageous in another

91
Q

advantageous vs disadvantageous alleles example

A
  • UV damages folate for neural birth defects
    — alleles that increase pigmentation would be advantageous
  • UV is required for vitamin D production and without causes rickets in bone
    — alleles that increase pigmentation would be disadvantageous in a sunny environment
    — alleles that decrease pigmentation would be advantageous in a less sunny envt.
92
Q

frequencies of alleles/phenotypes vary across populations due to…

A

generations of different selection pressures and limited gene flow

93
Q

crossing over between 2 genes generates

A

recombinant chromosomes

94
Q

if the ratio is not 1:1:1:1….

A

the more common of gamete will be the parental types

when crossing over occurs

95
Q

crossing over between 2 genes does not always happen…

A

so >50% of gametes will be parental. Fewer offspring will be recombinant.

96
Q

cis dihybrids

A

dominant alleles are on the same homolog

AB/ab

97
Q

trans dihybrids

A

dominant alleles are on different homologs

Ab/aB

98
Q

cis and trans dihybrids differ in…

A

what allele combinations are parental vs recombinant

(parental vs recombinant combos swap with cis and trans switch)

99
Q

parental offspring are…

A

more common than recombinant in terms of expected ratios

– exact ratio depends on the distance

100
Q

the farther apart genes are on a chromosome…

A

the more likely that they are to be affected by a crossover

(recombination is common)

101
Q

when genes are close together…

A

fewer crossover events occur and recombination is rare.

102
Q

calculation recombination frequency:

A
  1. do a test cross of dihybrid (heterozygous with recessive genotype)
  2. determine which offspring are recombinant
  3. add up recombinants and divide by the total offspring
103
Q

RF = 0%

A

complete linkage
(only parental genotypes)

104
Q

RF < 50%

A

linkage
(parental genotypes are more common)

105
Q

RF = 50%

A

independent assortment
(parental and recomb are equally likely)

genes are UNLINKED and independently assort despite being on the same chromosome

106
Q

RF will never…

A

exceed 50%

107
Q

recombination frequencies

A

measurements of “genetic distance” between genes

aka 1% RF = 1 map unit (m.u. OR centiMorgan cM)

108
Q

map unit

A

unit of measure of genetic distance correlating with 1% RF = 1 m.u. OR centiMorgan cM

109
Q

determine location of genes with RF %

A
  • the largest % will be the farthest apart
  • convert % to mu and add together to get distances between genes
110
Q

getting probability of recombinance with map unit

A

6 mu = 6% will be recombinant

  • do a test cross and determine the parental and recomb genotypes
  • divide % by 2 and assign % to each recomb.
  • remaining % out of 100% divided by 2 will be the parental types

ex/

3% each recomb
47% each parental

1/2 of each recombinant will be of each recombinant type.

111
Q

recessive lethal allele

A

an allele that prevents survival of homozygotes
- although heterozygotes carrying the allele survive

112
Q

incomplete-/co-dominance changes only…

A

phenotypic ratios NOT genotypic ratios

113
Q

complex traits

A

traits controlled by multiple genes and often also by environmental factors
- discrete or continuous

114
Q

temperature sensitive alleles

A

function depends on the environmental temperature

(permissive conditions allows for allele; restrictive does not)

115
Q

conditional lethal

A

allele that is lethal under certain conditions (permissive vs restrictive)

116
Q

hypostatic gene

A

gene (and its genotypic effects) that is being masked by the epistatic allele

117
Q

recessive epistasis

A

the effects of recessive alley at one gene hid the effects of alleles at another another gene

118
Q

dominant epistasis

A

the effects of a dominant allele at one gene hide the effects of alleles at another gene

119
Q

what does recessive epistasis indicate?

A

the dominant allele of the 2 genes function in the same pathway to achieve a common outcome

120
Q

what does dominant epistasis indicate?

A

the dominant alleles of the 2 genes have antagonistic functions

121
Q

redundant gene action

A

only 1 dominant allele of either of the 2 genes is necessary to produce phenotype

15:1 ratio

122
Q

complementation test defintion

A

methods of discovering whether 2 mutations are in the same or separate genes

123
Q

complementation test results

A

all WT (complementation occurs)
- strains had mutations in different genes
all mutant (complementation DNE)
- strains had mutations in the same gene

124
Q

linked

A

genes whose parental allele configurations are inherited more often than not; typically located close together on the same chromosome

125
Q

limitations of crosses to determine gene positions….

A
  1. difficult to determine gene order if some gene pairs lie very close together
  2. actual distances on map may not always add up
126
Q

bombay phenotype order

A

no antigen (FUT 2 gene) –> H antigen (glycotransferase A or B) –> A or B (attached to H)

127
Q

recessive epistasis

A

when recessive allele of one gene controls the expression of all alleles of the second gene.

9:3:4

128
Q

dominant epistasis

A

when the dominant allele of one gene hides the expression of all alleles of another gene

12:3:1

129
Q

complementary epistasis

A

need at least one dominant allele of both genes to get one phenotype and all other combinations give another phenotype
- both dominant alleles of both genes is necessary for dominant phenotype — otherwise shows recessive genotype

9:7 (dominant both: recessive either or both).

130
Q

duplicate gene epistasis

A

whenever there is a dominant allele concealing the expression of recessive alleles at two loci
– meaning at least one dominant allele of either of the 2 genes will cause a dominant phenotype

15:1

131
Q

linkage

A

the closeness of genes or other DNA sequences to one another on the same chromosome.

The closer two genes or sequences are to each other on a chromosome, the greater the probability that they will be inherited together

132
Q

if unlinked test cross…what proportion will have certain genotype?

A

25%

1:1:1:1 ratio

133
Q
A

genetics (5 decks)

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