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midterm 2 Flashcards

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1
Q

linkage

A

the association of two genes on the same chromosome

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2
Q

Case 1

A

-the most common

-wild-type allele is fully dominant to the mutant allele

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3
Q

haplosufficiency

A

one wild-type allele is sufficient to show phenotype in heterozygous state

therefore, mutated alleles are recessive

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4
Q

are mutant alleles recessive or dominant

A

recessive

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5
Q

case II

A

mutant allele is fully dominant to the wild type allele

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6
Q

explanation I for case II

A

haploinsufficiency
-one dose of the wild type allele is not enough to show wild type phenotype

therefore, mutated (null) allele is Dominant

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7
Q

is mutated allele is Dom or ress

A

Dominant

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8
Q

Explantion II for case II

A

the mutant allele (dom neg) makes the wild-type allele non-functional

(mutant product acts as a “spoiler’)

-gene product forms a homodimer, and one defective polypeptide interferes with its function

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9
Q

neomorphic allelles

A

mutation confers a new function to the gene

ex- the replacement of antennae with legs

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10
Q

what are the cases where one allele is not completely dominant over the other:

A

-incomplete dominance

-co-dominance

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11
Q

incomplete dominance ex

A

true breeding red-flowered snapdragons are crossed with true breeding white-floured snapdragons to produce pink-floured snapdragons

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12
Q

What are the ratios if the heterozygote has a phenotype distinct from either homozygote

A

the phenotypic ratio will be the same as the genotypic ratio

Geno ratio: 1 RR: 2 Rr: 1rr

pheno ratio: 1 red: 2 pink: 1 white

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13
Q

Incomplete dominance - molecular mechanism

A

two wild-type allele ‘doses’ produce the largest amount of gene product
=largest amount of functional protein product
=large amount of pigment (red flowers)

single wild type allele dose produces only half gene product
=less functional product
=less pigment (pink flowers)

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14
Q

Co-dominant allele

A

heterozygous individual has a phenotype showing characteristics of both homozygous individuals: blood groups

blood grouping involves interacation between antigen and antibody

A, B, AB, O

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15
Q

complete dominance

A

the heterozygous individual is indistinguishable from the homozygous dominant individual

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16
Q

incomplete dominance

A

the heterozygous individual has a distinct phenotype from either homozygous individual

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17
Q

codominance

A

the heterozygous individual has phenotypic characteristics of both homozygous individual

(no one dom over other)

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18
Q

lethal alleles

A

alleles that kill.

mutation in an essentail gene causes death of the individual

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19
Q

conditional alleles

A

phenotype expressed under one condition (permissive), but not in another condition (restrictive)

ex: temp. sensitive alleles, simease

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20
Q

penetrance

A

the % of individuals with a given genotype who exhibit the phenotype associated with that genotype

% expression of a phenotype in allelic combination carrying population

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21
Q

Expressivity

A

the extent to which a given phenotype is expressed in an individual

ex: spots in dogs

-all dogs have allele Sp but the expressivity of allele Sp varies between individuals

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22
Q

genes control-

A

biochemical reactions

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23
Q

Neurospora haploidy

A

helps to identiify the phenotype in F1 generation

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24
Q

beadle and tatum mutagenized neurospora and found several mutants with-

A

defective nutrition-assocaited reduced/ no growth

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25
learn beadle and tatums experiment
ad
26
beadle and tatum hypothesized that-
biosynthetic pathways are a series of steps, each step controlled by a gene =if a step is non-functional (due to mutation), pathway cannot be completed unless product of step is externally supplied
27
downstream compounds feed-
upstream mutants
28
beadle and tatum experiment conclutions
1) mutations in different genes (auxotrophs) represent unique defects within the biosynthetic pathway 2) each wild type gene controls a different step by making a different enzyme which controls a unique step 3) steps within biosynthetic pathway are controlled by enzymes
29
biosynthetic pathway consists of a series of steps, each step controlled by a unique enzyme that is made by a unique gene =
one-gene-one-enzyme hypotheisis -modified to one gene produces one polypeptide since some enzymes are muiltiple polypeptides
30
what is the alternative experiment to identify genes in same metabolic pathways
cross-feeding experiments
31
objective 3
if mutations causeing similar phenotypes are in the same or different genes complemention -> provide whats missing
32
possiblity #1 complemention test
the 2 mutants are alleles of different genes, A and B
33
possiblility # 2 complemention test
the 2 mutants are alleles of the same gene, A
34
how to know if its possibility # 1 for complemention test
2 mutants complement eachother, therefore, they represent alleles of the different gene
35
how to know if its possibility # 2 for complemention test
the 2 mutations do not complement each other, therefore, they represent two alleles of the same gene
36
what is step 1 for identifying what possibility it is (same or different genes)
identify the dominance or recessiveness of alleles -cross the mutants with wild-type plant
37
what is step 2 for identifying what possibility it is (same or different genes)
identify the relationship of alleles with each other cross the mutants with each other
38
rules for complementation test
1) can only be done with recessive mutations 2) if the mutations are different genes, the 2 mutations will complement one another (progeny will have wild type phenotype) 3) if the mutations are alleles of the same gene, the two mutaions will not complement one another (progeny will have mutant phenotype)
39
objective 4
understand how the phenotype of a double mutant can be used to infer the relative positions of genes in a pathway
40
if genes act independently (no interaction) =
9:3:3:1 phenotypic ratio
41
if genes segregate independently but genetically interact =
complementary gene action epistasis suppression redundancy all = modified dihybrid ratios (9:3:3:1)
42
complementary genes
independent but genetically interacting
43
genes act in the same pathway
mutations in genes for a target protein (product of a +) and its regulator (r+) give the same phenotype, as does the double mutant (9:7 ratio in F2)
44
epistasis
interaction in which one gene masks the effect of another gene
45
upstream mutants are -
epistatic to downstream mutants
46
suppression
a mutation in one gene reverses the affect of a mutation in another gene, resulting in a wild type phenotype in the double mutant
47
suppressor bypasses the block in-
pigment formation
48
complete dominance T
alleles which, when combined in the heterozygote show a phenotype indistinguishable from one of the homozygotes
49
haplo-sufficiency T
one copy of the normal gene is able to confer a normal phenotype
50
haplo-insufficiency T
one copy of the normal gene is unable to confer the normal phenotype
51
codominace T
alleles which, when combined in the herterozygote show phenotypic characteristics of both homozygotes
52
incomplete dominance T
alleles, which when combined in the heterozygote show a phenotype intermediate between the homozygotes
53
lethal allele T
an allele whose expression results in the death of the individual expressing it (may be recessive or dominant)
54
pleiotropic mutation T
a mutation that affects several different phenotypic characteristics
55
prototrophs T
an organism that will survive on minimal medium (carbon source, inorganic salts, water)
56
auxotrophs T
an organism that will not survive on minimal medium, but whose growth depends on supplementation of medium with a specific substance
57
complementation test T
a test for determining whether two mutations are in different genes (they complement) or the same gene (they fail to complement)
58
heterokaryon T
a cell composed of different nuclear types in a common cytoplasm
59
epistasis T
the phenotype of a mutant allele at one gene overrides the phenotype of a mutant allele at another gene, such that the double mutant has the same phenotype as the first mutant
60
suppression T
a mutation in one gene can cancel the effect of a mutation in a second gene, resulting in a wild type phenotype
61
genetic redundancy (duplicate genes) T
two independent genes that produce the same phenotypic effect when present individually or when present together
62
penetrance T
the proportion of individuals with a specific genotype who show that genotype phenotypically
63
expressivity T
the degree to which a particular genotype is expressed in the phenotype
64
complementary gene action ratio
9:7
65
recessive epistasis ratio
9:3:4
66
dominant epistatsis ratio
12:3:1
67
suppression ratio
10:3:3, 10:6, 13:3
68
redundancy
15:1
69
linkage or linked genes
-the genes or genetic loci that are on same chromosome and are tend to be inherited together
70
1:1:1:1
raio of dihybrid test cross progeny
71
9:3:3:1
ratio of dihybrid selfing F2 prgeny
72
independent assortment produces ____ recombinants
50%
73
configuration of alleles in parental lines is more common in-
in test cross progeny
74
dominants are together, recessives together =
coupling = cis (adjacent) conformation (pr . vg)
75
alleles are in repulsion =
trans (opposite) configuration (pr+ . vg)
76
if we do not know that genes are linked, we separate genes with -
"." pr/pr+ . vg/vg+
77
if we know genes are independently assorting (unlinked), separeate gene paris with -
";" a/a+ ; b/b+
78
if we know genes are linked, we use-
a slash to separate the 2 homologue pr+ vg+ / pr vg (cis dihybrid) pr vg+ / pr+ vg (trans dihybrid)
79
linked genes
are on the same chromosomes
80
linkage
-alllele combination in the parents are more likely to stay together through subsequent generations is independent of dominace/recessive
81
dominant alleles pair together ->
alleles in coupling or cis config/ cis-dihybrid pr vg/pr+ vg+
82
a dominant and a recessive allele pairs ->
alleles in repulsion or trans config/trans-dihybrid pr+ vg/pr vg+
83
muiltiple crossovers can include more than two chromatids
-several crossovers take place along chromosomes -the crossover events can take place between more than chromatids
84
if there are no crossovers we are talking about-
parental combinations
85
meiosis with a crossover we have -
parental combinations and recombinants
86
two processes generate recombinant products
1: independent assortment of genes on different chromosomes 2: crossing-over between genes on the same chromosome
87
principle of linkage maps
regions farther apart on a chromosome are more likely to have more crossover events as compared to loci closer to each other therefore, crossover frequencies should reflect linear relationship between distance
88
closer genes =
harder for genes to cross
89
for linked genes, recombinant frequencies are less than
50 %
90
if 2 genes are more than 50 cM apart on the same chromosome, crossing over will occur in every meiosis resulting in 50% recombinant. therefore, recombinantion frequency never exceeds-
50%
91
the farther apart the genes are the -
less accurate your mapping becomes
92
interference
a measurement of the independence of two cross-over events - (does one cross-over interfere with the possibility of another cross-over)
93
calculating interference
if crossovers are independent of each other, frequency of two cross-overs should be the product of their individual probabilities
94
negative interference
more double-crossovers than expected (cross-over in one region promotes cross-overs in another region) bigger than 1 observed is bigger than expected
95
positive interference (usually)
fewer double-crossover than expected (cross-over in one region inhibits cross-over in another region) less observed crossover events than expected
96
Negative interference =
more DCO than expected something is promoting more crossovers
97
Positive inerference
less DCO than expected so something is inhibiting crossover events
98
What is a+ mean
a wildtype
99
what does just a mean
mutant
100
parental ditype (PD)
simple, no cross over
101
nonparental ditype (NPD)
all recombinants or crossovers with eachother
102
tetratype (TT)
two parental combinations and two recombinants
103
mapping ordered tetrads
chromosome within spores of octad reflect position of chromatids during meiosis
103
if there is a 4:4 ratio (order + number) on M1 than
2 sister chromatids in each homologue were identical no crossover had occured between the gene and centromere
104
if there is a 2:2:2:2 ratio with alleles after M2 than
2 chromatids linked by the centromere were not identical a cross-over had occured between the gene and the centromere
105
parent = trans or cis?
trans
106
cis =
recombinant
107
linkage T
the association of two genes on the same chromosome
108
coupling configuration T
arrangement of linked alleles in a dihybrid such that the two dominant alleles are on a chromosome, the two recessive alleles are on the other chromosome ( AB/ab)
109
repulsion configuration T
arrangment of linked alleles in a dihybrid such that a dominant and a recessive allele are together on each chromosome ( Ab/aB)
110
cis dihybrid T
a dihybrid in which the alleles are coupled (AB/ab)
111
trans dihybrid T
a dihyrbid in which the alleles are in repulstion (AB/aB)
112
tetrad T
the four haploid product cells from a single meiosis
113
octad T
an ascus containing eight ascospores, produced in specied in which the tetrad normally undergoes a postmeiotic miotic division
114
first divistion segregation T
different alleles go into different nuclei at the first meiotic division producing an MI division pattern of ascospores
115
second division segregation T
different alleles go into different nuclei at the second meiotic division producing an MII division pattern of ascospores
116
molecular marker T
a site of DNA heterozgosity (difference) not necessarily associated with phenotypic variation, used as a tag for a particular chromosomal locus
117
single nucleotide polymorphism (SNP) T
A nucleotide pair difference at a given location in the genomes of two or more naturally occurring individuals
118
restriction enzyme T
-restriction endonuclease -an enzyme that will recognize specific target nucleotide sequences in DNA and break the DNA chain at those points
119
simple sequence length polymorphism (SSLP) T
the presence of different numbers of short or simple reptitive elements at one particular locus in different homologous chromosomes
120
haplotype T
a genetic class described by a sequence of DNA or of genes that are together on the same physical chromosome -a chromosomal segment defined by the array of markers it carries)

genetics (14 decks)

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