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biol 202 > Nilson1 > Flashcards

Nilson1 Flashcards

1
Q

What is reductive vs non-reductive division?

A

Non reductive → in mitosis and in meiosis II, it is a division that doesn’t change the ploidy of the cells

Reductive → in meiosis I, reduces the ploidy

*Meiosis I goes from diploid → haploid (with 2 copies of each because of replicated DNA)

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2
Q

What is the effect of colchicine?

A

It double the number of chromosome by preventing the cell from dividing

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3
Q

What does alloploid and autoploid mean?

A

Alloploid → more than 2 sets of chromosomes froming a hybrid of at least 2 different species

Autoploid → more than 2 sets of chromosomes from the same species

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4
Q

What are possible ways to induce polyploidy?

A

Spontaneous:
1. Fertilization by multiple sperms (ex: dispermy)
2. Errors in meiosis → diploid germ cells

Induced/intentional:
1. Disruption of chromosome segregation (plants) → colchicine
2. Fertilization by diploid germ cell from a tetraploid plant → Selective Breeding

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5
Q

What does euploid and aneuploid mean?

A

Euploid = full sets of chromosomes
ex: ABC, AABBCC

Aneuploid = not all sets of chromosomes are complet
ex: AABBC → 2n-1

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6
Q

What is a monosomic and trisomic set of chromosomes?

A

monosomic → 2n - 1
trisomic → 2n + 1

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7
Q

What is a Raphanobrassica?
Why could it not be fertile?

A

Raphanus = radish (2n = 18)
Brassica = cabbage (2n = 18)
Raphanobrassica = cross between radish and cabbage (2n = 18 because gets n = 9 from each)
Example of alloploidy!!

  1. But might not have all the genes it needs to reproduce
  2. Also, chromosome might not recognize each other to pair in meiosis I → can’t segregate equally → aneuploid gametes
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8
Q

What is the effect of crossing an alloploid back to one of its parent species?
Ex: Raphanobrassica x Brassica

A

It creates a new species

Gametes of a FERTILE Raphanobrassica (needs spontaneous double compared to normal infertile):
- 2n + 2n = 18 + 18 = 4n = 36 chromosomes
- Each gamete need nR AND nB to be viable
Gametes of Brassica = nB

F1 → gametes = nR + nB + nB → viable, but when gametes try to divide in meiosis nB pairs with nB and nR is randomly segregated → aneuploid gametes
F1 would be sterile → no F2

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9
Q

What are the viable trisomies?

A

Klinefelter Syndrome → XXY
Down syndrome → trisomy 21
normal → XXX
normal → XYY

*Trisomy 13, 18 → die in infancy, other trisomies die in the utero

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10
Q

What is the only viable monosomy?

A

Turner Syndrome → XO

*Aneuploidy affects gene dosage

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11
Q

What is the effect of non-disjunction in meiosis 1?

A

Homologous chromosomes fail to separate → 2x (1n + 1) + 2x (1n - 1)
The whole pair goes to 50% of gametes and none to the other 50%

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12
Q

What is the effect of non-disjunction in meiosis 2?

A

Chromatid sisters fail to separate → 2x (1n) non-affected + 2x (1n + 1)

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13
Q

What is cri-du-chat Syndrome?

A

It is a Deletion in on of the chromosome 5

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14
Q

How can chromosomal deletions happen?

A
  1. By breakage and rejoining → 2 break points, middle segment lost
  2. Crossing over between repetitive DNA → some repeats forming a loop are lost
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15
Q

What is Williams Syndrome deleiton?

A

Found in 1/10,000 people
1.5-Mb deletion on one homolog of chromosome 7 (7q11.23)

PMS repeats at both ends of a 17 gene segment → unequal crossover with other homologous chromosome → 1 has none of that 17 gene segment, 1 has a duplication
*Crossover between flanking regions

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16
Q

What is 1 technique to detect chromosomal deletions?

A

Use a complementation test:
Tester = many recessive mutations → if you see the pheontype for these mutation, it means the gene has been deleted

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17
Q

What are the different types of chromosomal rearrangements?

A
  1. Duplications (large ones are called segmental duplications)
  2. Inversions
  3. Chromosomal translocation
    FINISH
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18
Q

When do chromosomal inversions in somatic cells have a noticeable effect?

A

When they cut in the middle of a gene or 2 genes

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19
Q

What is the effect of chromosomal inversion in the germline?

A

Problem occurs when genes align → inversion loops

Paracentric heterozygot → does not include the centromere → dicentric chromosome (→ breakage) → loss of acentric fragment and major deletions
4 possible results of chromosomes (still have centromeres): Normal product, inversion product, deletion product with combination of both, deletion product with only 1

Pericentric → includes the centromere → products with major deletions

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20
Q

What are the somatic consequences of chromosomal translocation?

A

L-type misalignement → have to align with same genes
Possibility 1: Both products are incomplete (1 normal chromosome + 1 half-half)
Possibility 2: Both products are complete (2 chromosomes with half of each on each for each gamete)

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21
Q

What is a balanced Robertsonian translocation? What does it lead to?

A

Fusion of 2 acrocentric chromosomes (chromosomes with centromere near one end) → single chromosome with single centromere and loss of both short arms

Occurs in one of the gametes → at fertilization (with other normal gamete), can give rise to trisomy (or not)
Can result in inheritance of trisomy 21 (SLIDE 20 L18)

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22
Q

What is the biology of maize (corn)?

A

Endosperm (3n) = sperm cell (n) + central cell (2n)
Embryo (2n) = sperm cell (n) + egg cell (n)

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23
Q

What are different alleles for the maize pigments?

A

c = recessive allele → unable to make pigments
C = dominant allele → production of purple pigment
C’ = dominant inhibitor → represses pigment production

C’ > C > c

24
Q

What are the important genes on chromosome 9 of the maize?

A

Endosperm (3n) → sperm cell (n) + central cell (2n)

C’ + Ds on chromosome 9 from sperm cell (n)
C on chromosome 9 from central cell (2n)

On both chromosomes 9:
Knob - Colored - Shrunken - Bronze - Waxy - Ds - Centromere

25
Q

What explains the purple dotted phenotype of the maize?

A

C’ on the sperm cell’s (n) chromosome 9 is lost (Ds breakage)

Ac allele on another chromosome from the central cell (2n) allows Ds to jump close to C’ → breaks the chromosome → loss of C’ → C is now dominant

Breakage of C’ uncovers C which allows pigment to be produced → dots
*I maize = 1 cell so pigments in the cell, not many cells

26
Q

Why would a maize appear fully yellow even if it has C’ and Ds on chromosome 9 of the sperm cell (n)?

A

If the other chromosome from the central cell (n) lacks Ac allele → Ds is stable, can’t jump → No breakage in chromosome 9 → C’ stays and dominantly inhibits pigment production

27
Q

How could the phenotype of a purple kernel with yellow dots apear?

A

Sperm cell (n) has C and Ds
Another chromosome (from any of the 2 cells) has Ac element → cuts C allele off

c allele is incovered (from chromosome 9 of the central cell (2)) → stops producing pigments → yellow dots

28
Q

What are autonomous vs non-autonomous transposable elements?

A

Autonomous → jump on their own (ex: Ac), encode their own transposase enzyme

Non-autonomous → require another element to jump (ex: Ds requires transposase activity from Ac to jump)

29
Q

What does the spot size on the dotted kernels depend on?

A

It depends on when, during endosperm development, the C gene became active

*Ds can also jump into C??

30
Q

What are the 2 classes of transposable elements?

A

Class 1 → Retrotransposons (eukaryotes)
Class 2 → DNA transposons (prokaryotes and eukaryotes), ex: Ds, Ac elements, P-element

31
Q

What explains the change in colour of grapes?

A

Black grapes → produce pigment (pigment gene)

Green grapes → LTR retro-element disrupts the promotor region of the pigment gene → no pigments produced

Redish grapes → LTR recombination between 2 flanking sequences (LTR) → small inhibition, but still a bit of pigment production

32
Q

What explains the change in phenotype from white to dark moths?

A

White moths = WT cortex gene

Dark moths = 22-kb TE insertion inside the cortex gene → Natural selection

33
Q

What do transposable elements lead to?

A

Lead to mutations + genome instability

34
Q

Explain the experiment leading to the discovery of P-elements in drosophila.

A

*P-element (transposase gene)
M strain = lab
P strain = wild caught (contains P elements)
1. Crossed M females x P males → non-fertile F0 (germling cells don’t develop) → no offspring
Because no transposase silencing in the P male → jumps in the females chromosomes

  1. Crossed P females x M males → fertile F0 → normal descendence
    In female P embryonic germ-line cells, P-element motility is silenced → doesn’t jump into males chromosomes or elsewhere
35
Q

What fraction of the human genome is occupied by LINEs, SINEs and DNA transposons?

A

LINEs (class 1) → Autonomous, 1-5 kb, 21%
SINEs (class 1) → Non autonomous, 100-300 bp, 13%

DNA transposons → Autonomous (2-3kb)/Non autonomous (80-3000 bp), 3% total

*About 20x as much DNA in the human genome derived from transposable elements as there is DNA encoding all human proteins
*Transposable elements are abundant in large genomes (ex: 54% in human)

36
Q

What accounts for differences in genome sizes in plants? (that are not that far in species trees)

A

Transposable elements

37
Q

Where are transpoable elements usually found in the genome?
Why?

A

Found in introns or intergenic regions

When they are found in exons → disrupt ORF → leads to lethality → strong selection against these

38
Q

What is Tc1?

A

It is an autonomous DNA transposon found in C. elegans ~ 32 copies in their genome

It transposes in somatic cells, but not in the germline cells → transposes gene in each Tc1 copy is silenced in the germline cells

39
Q

What experiment could identify the genes that cells use to repress transposable element mobility of Tc1?

A

By blocking the system that represses motility of Tc1, it can jump out of unc-22 and allow the worm to move fluidly

Do a genetic screen → mutate the geen at random → select worm in whic Tc1 element mobility is no longer repressed → isolate and study

It should be checked if the same gene is KO in each work by breading or complement test

Screens identified 25 genes that block Tc1 mobility → most of them involved in RNAi silencing pathway

40
Q

How is Tc1 mobility repressed?

A

*1 single Tc1 can repress all Tc1 mobility in a cell
*Example of genome surveillance!

  1. Processing of miRNA with dicer, etc.
  2. miRNA binds to the RISC complex
  3. miRNA/RISC complex recognizes mRNA targets through sequence complementarity → promote degradation or repress translation
41
Q

What is the difference between miRNA and siRNA?

A

miRNA = endogenous gene (microRNA), can affect multiple different but similar genes, binds 3’ UTR
siRNA = foreign gene (transgene, virus, TE), binds the ORF

42
Q

How does piRNA repress transposon mobility in the germ lines of Drosophila and other animals?

A

piRNA don’t start as double stranded RNA (as do siRNAs), start as part of long mRNAs from specific genmoe region called pi-clusters

  1. Transposable element inserted randomly into chromosome
  2. Inserted in the pi-cluster (randomly)
  3. piRNA made out of it
  4. With kiwi-argonaute → anneal and degrade complementary TE mRNA transcripted from elswhere in the genome → Genome surveillance

*A TE will be transcribed until it jumps in the pi-cluster and has a piRNA

43
Q

What explain thefact that M stain (lab) does not see motility of the P element compared to P strain?

A

piRNA for P element is present in M strain, not in the P stain

44
Q

What is one of the roles of p53 in tumour suppression?
How was it tested?

A

the hypothesis is that it would repress transposable element motility

p53 mutant showed elevated LINE-1 ORF1p expression → tumorgenesis
*in human and drosophila

45
Q

What happens when Ds jumps into the C allele in chr 9 of the the sperm cell of the maize?

A

Creates a c-m1 allele (requires presence of Ac for jump of Ds)
~1/4000 → rare kernel
Ds excision gives blue sectors as a phentoype for c-m1 and c (on the other chr9)

46
Q

What can happen to offspring that inherit C-Ds and c alleles on chromosome 9 as whell as Ac (on either sprem or central)

A

The offspring starts out making colorless kernels → Somteimes as the cells of the endosprem divide → Ac activates Ds loss of C gene → Ds jumps out → WT C allele gives rise to pigmented kernel (spots of purple with colorless background)

The spot size depends on when during endosperm development, the C gene became active

47
Q

How do Ds and Ac elements in maize jump around?

A

They are in the same family of DNA transposons → each family has different autonomous and non-autonomous elements + each family has a transposase version specific to its family

Ac is autonomous because it encodes for its own transposase
Ds requires Ac to encode for the transposes

  1. Transposase binds to ends of Ac and Ds elements
  2. Cleavage of the DNA segment (form an excision loop)
  3. Integration into a new target site
48
Q

Considering the recessive fa mutant allele is from bp 33-50. Would is be expressed when combined with a chromosome with a 32-66 deletion? With a 2-14 deletion?

A

Would be expressed in the combination with 32-66 because would be pseudo-dominant

Would be recessive to the real fa allele in the chromosome with deletion 2-14

49
Q

P and Bz are normally 36 m.u. apart on the same arm of a certain plant chromosome. A paracentric inversion spans about 1/4 of this region but does not include either loci. What approximate recombinant frequency between P and Bz would you predict in plants that are:
a) Heterozygous for the paracentric inversion?
b) Homozygous for the paracentric inversion?

A
  • Paracentric → does NOT include the centromere
  • 1/5 of the region → will occur 1/4 of the time there is a recombinant in that region (36 % of the time)
    → RF for heterozygous (1 inverted, 1 not) → inversion loop ~ 27% bc product of crossing over is NOT viable
    *Same if pericentric → crossover products not recovered

For homozygous (both chromosomes inverted → no inversion loop), product of crossing over is viable to RF ~ 36 %

*Occurs during meiosis, not mitosis!

50
Q

What is the cause of most aneuploidy?

A

Non-disjunction

*To have non-disjunction, need to have crossover at start

*Aneuploidy affects gene balance dosage

51
Q

What are the only chromosome rearrangements that survive meiosis?

A

Chromosomal arrangements that have 1 centromere (needed for anaphase positioning) + 2 telomeres
*Acentric chomosomes are not inherited
*Dicentric will be broken and often degraded

52
Q

A fruit fly was found to be heterozygous for a paracentric inversion. However, obtaining flies that were homozygous for the inversion was impossible. What is the most likely explanation for this inability to produce a homozygous inversion?

A

One of both breakpoints of the inversion are located within an essential gene causing a recessive lethal mutation

53
Q

What type of gene is the white gene in drosophila?

A

white allele → X-linked recessive allele
WT → red color

If have mariner transposon → wm → white eye phenotype

54
Q

How could you test the hypothesis that a transposable element is present and responsible for the different phenotypes of pigment color?

A

To test the hypothesis:
- White x white
- Blue x white
Both have the transposable element

55
Q

Why can’t retrotransposons move from one cell to another like retroviruses?

A

Because they do not encode the Env protein

56
Q

An Alu element inserts into the 3’ splice (AG) sit eof an intron in a human gene. What will be the effect?

A

The Alu element will be transcribed into RNA with the rest of the gene sequences and will prevent the splicing of the intron that is has inserted into

→ almost certainly result in a null allele as the Alu sequence and the intron will now be translated

→ The intro, Alu, or both probably will contain stop codons

57
Q

Can intron indels cause frameshit mutations?

A

No, because spliced out before translation

biol 202 (7 decks)

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