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Test 3 Flashcards

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1
Q

what are the units of transmission in meiosis

A

chromosomes

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2
Q

what cannot undergo independent assortment

A

linked genes

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3
Q

what is the frequency of crossing over on a single chromosome proportional to

A

the distance between them

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4
Q

when does crossing over occur

A

always happens in meiosis and mitosis

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5
Q

what can occur because of crossing over, but does not always occur

A

recombination

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6
Q

what is recombination a result of

A

crossing over

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7
Q

chromosome maps

A

indicate the relative location of genes on a chromosome

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8
Q

T/F A linkage map is a physical map

A

F - its a probability map

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9
Q

what is the consequences of linkage in meiosis

A

independent assortment does not occur (if it does then there is no linked genes)

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10
Q

what is linkage without crossing over

A

complete linkage

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11
Q

what does linkage with crossing over result in

A

generates recombinant gametes

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12
Q

complete linkage

A

produces parental gametes

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13
Q

results of crossing over

A

between 2 non-sister chromatids, both parental and recombinants produced

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14
Q

what is a linkage group

A

the haploid number of chromosomes

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15
Q

how many linkage groups in humans

A

24

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16
Q

Linkage effects expected ratios because it violates which of Mendel’s postulates?

A

Homologs independently assort in meiosis.

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17
Q

chiasmata

A

synapsed chromosomes in meiosis wrapped around each other

x shaped intersections with points of overlap (points of genetic exchange)

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18
Q

what does the percentage of recombinant gametes depend on

A

distance between 2 genes on the same chromosome

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19
Q

genes close to each other on a chromosome are more or less likely to have chiasmata and recombine

A

less likely

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20
Q

recombination frequencies between linked genes are

A

mostly additive

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21
Q

what is 1 cM equal to

A

1% recombination between 2 genes on the chromosome

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22
Q

single crossovers

A

the relative distance between 2 loci influences the amount of recombination and crossing over, 1 cross over results in 2 recombination events

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23
Q

what do we assume if the genes are more than 50 cM apart

A

that they are on different chromosomes

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24
Q

double cross over

A

results from double exchanges of genetic material, 2 chiasmata

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25
Q

3 point mapping criteria

A

Genotype of organism producing crossover gametes must be heterozygous at all loci considered.

Cross must be constructed to determine genotype of all gametes by observing phenotypes of offspring.

Sufficient number of offspring must be produced for representative sample crossover.

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26
Q

steps for mapping a crossover

A
  1. identify parental chromosomes
  2. identify double cross overs
  3. figure out what is in the middle
  4. find which single cross overs pair up
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27
Q

how to know which criteria are the parents

A

highest numbers

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28
Q

how to determine the double cross overs

A

lowest number

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29
Q

how to figure out which gene is in the middle

A

compare parentals to double cross overs, the gene that doesn’t move is in the middle

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30
Q

what do recombination frequencies do?

A

approximate the switches, measures the detectable recombinant combos in products of meiosis

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31
Q

what is the largest recombinant frequency

A

outermost genes of the trio

32
Q

can crossovers always be detected why or why not

A

no, because a crossover event will not detect double exchange when an arrangement of alleles on non sister homologs are recovered

33
Q

what are the complications of multiple gene exchanges

A
  1. distance between gene is underestimated

2. most accurate gene maps are when genes are closer together

34
Q

interference

A

reduces the expected number of multiple crossovers when one cross over event in one region of the chromosome inhibits a second event nearby

35
Q

coefficient of coincidence

A

quantifies disparities resulting from interference

c=o/e

36
Q

what is the interferance equation

A

I=1-C

37
Q

what is the value of I if interferance is complete and their are no double cross overs

A

I=1

38
Q

what does it mean if i is positive

A

positive interference –> fewer DCO than expected

39
Q

what does it mean if I is negative

A

negative interference –> more DCO than expected

40
Q

what contributes to interference

A

physical constraints that prevent chiasmata

41
Q

forward genetics

A

start with phenotype and find genotype

42
Q

ways forward genetics is used

A

human genetic disease screens, linkage mapping

43
Q

reverse genetics

A

start with genotype and figure out phenotype

44
Q

ways reverse genetics is used

A

gene silencing, targeted mutagenesis, RNAi, CRISPR

45
Q

morpholinos

A

synthetic oligonucleotides 25bps long, target mRNAs to block their transcription, do not destroy the mRNAs, base pairs are same as RNA, bound to methylenemorpholine rings linked through phosphoramidite groups instead of phosphates.

46
Q

what is RNA interference

A

An ancient immunity pathway against transposable elements and/or viral elements
Also used for gene-regulation
Likely evolved at the base of the eukaryotes
Utilizes dsRNA

47
Q

siRNA

A

Double stranded
Binds to the complementary portion of the target mRNA
Targets the mRNA for degradation
Each strand has a 2-3 bp overhang small interfering) - 21-22 bps,

48
Q

miRNA

A

miRNA (micro) – 19-25 bps; encoded by the genome

49
Q

RISC

A

RNA Induced Silencing Complex – cleaves the mRNA
A complex of proteins; precise structure not yet resolved
The main component is Argonaute

50
Q

dicer

A

protein that cleaves the original dsRNA into siRNAs

51
Q

Steps for RNAi

A
  1. Inject dsRNA
  2. Dicer chops dsRNA into siRNA
  3. Argonaute puts siRNA in RISC
  4. Guide strand is kept in RISC, partner strand is degraded outside of the complex
  5. RISC uses a guide strand to recognize target mRNA
  6. the Argonaute in RISC chops up target mRNA
52
Q

what is miRNA

A

RNA interference that is indigenous, regulates gene expression

53
Q

what processing is needed for miRNAs

A

expressed as long pri-miRNA, then processed to pre-miRNA

54
Q

what cuts pri miRNA to pre miRNA

A

Drosha and posha

55
Q

what happens to the pre-miRNA

A

enters the cytoplasma, cut into 22 bp long by dicer
now mature miRNA
Integrated into the RISC with argonaute
argaunote can now use one strand as a guide

56
Q

eRNAi

A

embryonic RNAi

57
Q

mRNAi

A

maternal RNAi

58
Q

how can dsRNAs be used in lab

A

can be synthesized, just need the sequence of the mRNA

59
Q

main methods of reverse genetics

A

TALEN
Zinc Finger nucleases
CRISPR

60
Q

Mutation by a double stranded break

A

non homologous end joining

because the break ends are directly ligated without the need for a template

61
Q

What are zinc finger nucleases

A

artificial restriction enzymes made by fusion of zinc finger transcription factor domain and a DNA cleavage domain
must be used in pairs
very specific

62
Q

What are TALENS

A

transcription activator-like effector nuclease
restriction enzyme that can be engineered to cut specific sequences
made by the fusion of the DNA binding domain of a bacterial transcription factor (TAL) to a DNA cleavage domain

63
Q

how do TALs recognize DNA

A

through 34 AA repeat sequences, but the 12th and 13th position are hypervariable

64
Q

how many breaks will one talen complete

A

one, two would make a double break

65
Q

homologous recombination

A

sticky ends that look like donor and there are parts added to the break

66
Q

how is CRISPR used in nature

A

to combat viruses in bacteria

67
Q

how does CRISPR work in nature

A

Bacteria wants to remember it was attacked by a virus
The b cells have a memory of what it has been attacked with before
Bacterial genome has a CRISPR locus,
after bacteria is infected by virus we have DNA and we put it into memory bank/CRISPR locus
Spacers have the sequence specific to the virus

68
Q

what is Clustered Regularly Interspaced Short Palindromic Repeats

A

These are DNA sequences
Derived from bacteriophages that had previously infected the bacteria
Used to detect and destroy DNA from similar viruses during subsequent infections.

69
Q

What does CRISPR Cas do

A

Upon viral infection, bacteria use CRISPR-associated (Cas) proteins to cut off a piece of viral DNA
This sequence is integrated into the bacterial genome in between specific spacer regions
By storing it, the bacteria remember this virus and will be able to counter-attack it if it invades again
Repeat sequences- separate the spacer/viral sequences

70
Q

what are CRISPR spacer sequences

A

are transcribed into short RNA sequences (“CRISPR RNAs” or “crRNAs”) capable of guiding the system to matching sequences of DNA

71
Q

what happens when target DNA is found in CRISPR

A

Cas9 binds to it and cuts it

72
Q

tacrRNA

A

helps it get inot Cas9 machine and get it where it needs to go, partially complementary, helps it fit into the Cas 9 enzyme
Partially complementary to the crRNA; base pairs with the crRNA
Allows the formation of the Cas9-crRNA complex

73
Q

crRNA

A

Made from the CRISPR locus
Specific to the invading DNA virus
Guides the Cas9 protein to the target sequence

74
Q

what is the PAM

A

Protospacer Adjacent Motif
DNA sequence immediately following the DNA sequence targeted by Cas9.
PAM is a component of the invading virus or plasmid, but is not a component of the bacterial CRISPR locus
Cas9 will not successfully bind to or cleave the target DNA sequence if it is not followed by the PAM sequence
Cas9 cuts 3-5 bp upstream of the PAM sequence

75
Q

how is the guide RNA form

A

fuse the tracrRNA and the crRNA into a single RNA called the “Guide RNA (gRNA)”

76
Q

how to … CRISPR hacking

A

We need to target specific sequences that will adhere to the CRISPR rules…
The target site must be 20 bp- Not including PAM
Must have a PAM

Genetics (4 decks)

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