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BIOL 239 > Week 11 > Flashcards

Week 11 Flashcards

Chromosomal Rearrangements, Transposable Elements, and DNA Analysis

1
Q

define: chromosomal rearrangements

A

mutations occurring on a larger scale

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2
Q

is homozygosity for gene deletions always lethal

A

no, but it usually is

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3
Q

is heterozygosity for gene deletions lethal

A

it is usually detrimental

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4
Q

define: gene dosage

A

the number of times a given gene is present in the genome

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5
Q

what causes cri-du-chat syndrome

A

deletion on the short arm of chromosome 5

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6
Q

define: tandem duplications

A

duplications that lie adjacent to each other

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7
Q

can a tandem duplication be in reverse

A

yes

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8
Q

define: nontandem duplications

A

two or more copies of regions that are not adjacent to each other

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9
Q

do nontandem duplications occur on the same chromosome

A

they can be on the same chromosome or different chromosomes

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10
Q

do duplications have obvious phenotypic consequences

A

many do not

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11
Q

what does change in phenotype depend on for duplications

A

whether there is a gene-dosage effect for that genes product

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12
Q

what causes Fragile X syndrome

A

large number of duplications of a CGG repeat on the X chromosome

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13
Q

why is the CGG on the X chromosome for fragile X syndrome harmful

A

prevents the gene downstream of that region from being transcribed

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14
Q

what does unequal crossing between duplications cause

A

increases of decreases in gene copy number

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15
Q

how was myoglobin formed

A

duplication of β -globin gene and subsequent selection

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16
Q

what is the advantage of myoglobin

A

has a greater affinity for O2 than hemoglobin

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17
Q

do inversions and translocations result in a change of genetic content

A

no, it is just a change of distribution

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18
Q

when do inversions occur

A
  • following two double strand breaks
  • from rare crossovers between related DNA sequences present in two different locations on the same chromosome
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19
Q

define: paracentric inversions

A

exclude the centromere

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20
Q

define: pericentric inversions

A

include the centromere

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21
Q

how do chromosome 4 in humans and chimpanzees compare

A

differ by only a pericentric inversion

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22
Q

when do mutant phenotypes occur with inversions

A

if one end lies within a coding region of DNA

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23
Q

define: translocations

A

large scale chromosomal rearrangements in which part of one chromosome either becomes attached to another chromosome or parts of two different chromosomes trade places

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24
Q

define: reciprocal translocation

A

parts of two different chromosomes trade places

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25
define: robertsonian translocation
reciprocal translocations arising from breaks at or near the centromeres of two acrocentric chromosomes
26
what is the result of robertsonian translocation
one large and one small chromosome, small chromosome is usually lost
27
what causes Familial Down's syndrome
robertsonian translocation between C14 and C21 in the germ cell mated with a normal gamete
28
why is there a difference in chromosome number between humans and the great apes
robertsonian translocation occurred sometime in our evolutionary history
29
define: transposable elements
small segments of DNA which are able to move from one position to another in the genome
30
how much of the human genome consists of transposable elements
40%
31
who inferred the presence of transposable elements
Rhoades and McClintock
32
what does it mean for a transposable element to be selfish
only carries information required for their own propagation
33
what are the two kinds of transposable elements in prokaryotes
- insertion sequences (IS) - transposons (Tn)
34
how do insertion sequences move
by cut and paste
35
what do insertion sequences contain
terminal inverted repeats
36
what do insertion sequences code for
a transposase enzyme
37
what does transposase do
recognizes inverted repeats and cuts the host DNA for IS movement
38
what are the steps of insertion of IS into target DNA
1) staggered cleavage of target DNA 2) insertion of IS 3) synthesis of DNA fills gap
39
how do transposons move
by cut and paste
40
what do transposons code for
a transposase enzyme and other genes such as resistance genes
41
define: composite Tns
2 IS elements flanking one or two genes
42
what are the two kinds of transposable elements in eukaryotes
- transposons - retrotransposons
43
how do retrotransposons move
makes a copy of itself
44
how do retrotransposons move
via an RNA intermediate
45
how is the RNA intermediate of a retrotransposon inserted into the DNA
reverse transcriptase copies the RNA into a double-stranded DNA molecule for insertion into the genome
46
what are the two major classes of retrotransposons in mammals
- LINEs (long interspersed elements) - SINEs (short interspersed elements)
47
what is often the cause of unequal crossovers
transposable elements
48
what is an example of a result of transposable element insertions
yellow cauliflower
49
what are DNA probes
short single-stranded stretches of DNA of known composition
50
how long are DNA probes
from 25 to several thousand nucleotides
51
how are DNA probes visualized
they are labelled with 32P or fluorescent dyes
52
what are DNA probes used for
identification of clones that contain complementary DNA sequences
53
what are the steps of screening libraries by hybridization
1) plate bacteria carrying recombinant DNA and incubate until colonies form 2) replica-plate colonies 3) lyse cells, denature and bind DNA to the membrane 4) add DNA probe and incubate under annealing conditions 5) rinse membrane to remove non-annealing DNA 6) expose to X-ray film 7) pick corresponding colony from plate and isolate recombinant DNA
54
what do dark spots on X-ray show
recombinant, positive hybridization
55
what are the requirements of hybridization probes
- region of complementarity between probe and target sequence must be long enough to allow sufficient hydrogen bonds to provide a cohesive force In General - longer than 50-100 bp - complementarity is more than 80%
56
what is southern blot analysis used for
showing the location of a gene within a larger fragment of DNA
57
what are the steps of southern blot analysis
1) transfer DNA fragments from agarose gel to nitrocellulose filter paper 2) perform hybridization between a labelled probe and DNA on the filter 3) expose to X-ray film to identify hybrid
58
what is a use of southern blot analysis
identification of patients with tuberculosis
59
who invented polymerase chain reaction (PCR)
Dr. Kary Mullis
60
what is the method of PCR
1) design two primers that are complementary to each end of the sequence of interest 2) mix the primers, template DNA, thermostable DNA polymerase, and the 4 nucleotide bases in a microtube 3) begin thermocycling procedure
61
what are the steps of thermocycling for PCR
1) denature: 94°C for 5 min 2) anneal: 50-60°C for 2 min 3) extend: 72°C for 2-5 min (repeat)
62
how does PCR work so quickly
each cycle of PCR results in an exponential duplication of the strands
63
where is PCR used
- diagnosis of infection - paleomolecular biology - forensic science
64
what is the basis of sanger dideoxy sequencing
based on lack of 3' OH group to terminate chain elongation
65
how does sanger dideoxy sequencing work
- mix DNA polymerase with dATP, dGTP, dCTP, dTTP - put in tubes with ddA, ddG, ddC, and ddT that are uniquely labelled - separate strands on polyacrylamide gel
66
why is polyacrylamide gel used in sanger dideoxy sequencing
it can resolve strands that differ in length by a single nucleotide
67
how is DNA sequencing done in modern times (sanger dideoxy sequencing)
uses a laser and fluorescence detector on the gel
68
how is genetic testing for sickle-cell done
- PCR amplification of 500 bp fragment of interest then REN digestion with *Mst*II - normal allele will be cut and give 2 bands, sickle cell allele will only give one band
69
how is preimplantation genetic testing for cystic fibrosis done
- retrieve several ripe eggs from ovary, fertilize with sperm - at 6-10 cell stage, remove one cell from each embryo for genetic testing - lyse cell, isolate DNA - perform PCR amplification of site of common mutation - hybridize half with normal probe and other half with mutant probe - dark spot of X-ray means positive hybridization
70
what are the canadian genetic testing regulations
allows licensing of tests for genetic diseases based on: 1) high penetrance (90% threshold) 2) cannot be successfully treated 3) are of early onset

BIOL 239 (12 decks)

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