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Biol 200 > Lecture 27 - Chromosomes > Flashcards

Lecture 27 - Chromosomes Flashcards

1
Q

How errors of homologous recombination can happen

A

Unequal crossing over when many copies of certain DNA elements (like genes) are present in the genome

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2
Q

2 possible consequences of homologous recombination at gene level

A

1) Gene deletion

2) Gene duplication

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3
Q

Goal of chromosomes in metaphase

A

Highly condensed for transmission to daughters

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4
Q

Goal of chromosomes in interphase

A

Decondense (regulated) for transcription and regulation

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5
Q

What is though to be the structure of chromosomes during interphase method that proved it

A

Loops that always come back to a scaffold.

Genes localization by in situ hybridization

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6
Q

method that proved evidence for loops in interphase chromosome

A

Genes localization by in situ hybridization

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7
Q

To what extent are loops of chromatin dependent (2 levels)

A

Each one is independent in terms of chromatin condensation and enhancer action

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8
Q

Name for the scaffold of chromatin loops

A

SAR : Scaffold-associated region

MAR: Matrix-attachment region

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9
Q

Function of scaffold region (2)

A

1) Barrier to spreading chromatin condensation (boundary elements)
2) Barrier to action of enhancers

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10
Q

Length of a chromatin loop

A

1-4 Mbp

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11
Q

where lampbrush chromosomes are found + their size

A

In amphibian mature oocytes (1 mm diameter cells)

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12
Q

Charact. of lampbrush chromosomes (2)

A

Highly transcriptionally active for a long time + spread because cell is very large

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13
Q

What’s the name of giant chromosomes found in drosophila’s salivary gland + name of phenomenon observed

A

Polytene chromosomes -> cellular giantism

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14
Q

What causes cellular giantism

A

10 cycles of DNA replication without cell divison (1024 daughter chromatids)

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15
Q

Light bands vs Dark bands on polytene chromosome

A

Dark = condensed chromatin

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16
Q

What are polytene chromosome puffs associated to

A

Decondensed chromatin and transcription

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17
Q

How puffs visualized with CTD of Pol II

A

Red associated w/ phosphorylated CTD, green unphosph. Use antibody for CTD of Pol II

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18
Q

3 main regions found on a (replicated) chromosome

A

Sister chromatids, centromere, telomeres

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19
Q

Chromosome state when showing karyotype

A

Metaphase

20
Q

Chromosome painting explanation (how karyotype revealed)

A

Fluorescence in situ hybridization w/ panel of probes of distributed sequences

21
Q

Where chromosome breaks/translocations can occur

A

In somatic cell division in an organism

22
Q

What are chromosome breaks/translocations

A

2 chromosomes break (double strand break) and each ‘‘half’’ goes w/ ‘‘half’’ of other chromosome

23
Q

Example of chromosome translocation and special name of resulting chromosome and condition

A

Chromosomes 9 and 22. Small resulting chromosome = philadelphia chromosome. Chronic myelogenous leukemia

24
Q

What can cause chromosome translocations (2)

A

1) Nonhomologous end joining between the 2 (both were broken)
2) Errors in homologous recombination because of identical repeats

25
Q

Problem of chromosome translocations in germ line (cells leading to gametes)

A

Lead to inperfect alignement of chromosomes during meiosis and reduced number of gametes produced that contain all genes

26
Q

Why imperfect alignement of chromosomes during meiosis affects number of gametes produced

A

Perfect alignement of chromosome (disrupted by translocations )during meiosis is required to produce functional gametes

27
Q

What happens to organisms carrying variant chromosomes (received translocated chromosomes from mom or dad’s gamete)

A

Sterile/greatly reduced fecundity -> Can’t produce functional gametes : Chromosomes won’t be aligned perfectly during meiosis

28
Q

What explains fact that hybrids are sterile

A

If receive 2 gametes from different species, chromosomes won’t align perfectly during meiosis so they can’t produce functional gametes

29
Q

To what extent/on what scale the karyotype of a species changes and due to what

A

Changes in evolutionary time due to chromosome variants succesfully passes between generations

30
Q

3 elements absolutely required to replication and stable inheritance of chromosomes

A

1) ORI (at least 1)
2) Centromere
3) 2 telomeres (ends)

31
Q

Example of method used to check which regions in DNA are necessary for replication and stable inheritance of chromosomes

A

Grow yeast leu- (w/o leucine gene) with plasmids containing LEU and random DNA fragments, in a medium without leucine

32
Q

What is ARS + length

A

Autonomously replicating sequence (100 bp)

33
Q

Effect of putting LEU gene in plasmid w/ only ARS

A

Replicaton occurs but mitotic segregation is faulty (large proportion of cells don’t receive plasmid)

34
Q

Effect of putting LEU gene in plasmid w/ ARS and centromeric sequence

A

Replication occurs and mitotic segregation is successful

35
Q

Role of centromeric sequences

A

Equal partitioning/distribution of plasmid to daughter cells during mitosis

36
Q

Effect of putting LEU gene w/ ARS and centromeric sequence in a linear plasmid

A

No progeny to the daughter cell

37
Q

Effect of putting LEU gene w/ ARS, centromeric sequence AND 2 telomeric sequences in a linear plasmid

A

Linear plasmid behaves like normal chromosome (replication and mitotic segregation are successful

38
Q

Role of telomeric sequence

A

Promotes stability of chromosome so it can be passed for a long period of time

39
Q

Structure of centromeric sequence

A

Region 1 conserved
Region 2 AT rich
Region 3 conserved

40
Q

2 differences between yeast and higher eukaryotes about centromeric sequence

A

1) Higher eukaryotes : Longer region II (264 bp instead of 78-86 in yeast)
2) Yeast -> One or several repeats of CEN
Higher euk -> several repeats of CEN

41
Q

Special thing about centromeric nucleosomes

A

Contain special variant of histone H3 called CENP-A

42
Q

Utility of variant CENP-A in centromeric nucleosomes

A

Drives kinetochore assembly, which is what spindle microtubules will bind to

43
Q

Problem of the lagging strand mechanism

A

5’ end of daughter strands cannot be completed because no DNA put at the end after primer removal

44
Q

Solution to lagging strand mechanism

A

Telomerase, a DNA polymerase that extends telomeres to complete 5’ end of daughter strand

45
Q

In what cells of the body telomerase is active

A

Germ cells and stem cells (+ reactivated in cancer cells)

46
Q

What happens to mice missing telomerase gene

A

Are OK for 3 generations, and then fecundity declines

47
Q

Telomeric repeat in human telomeres

A

TTAGGG

Biol 200 (30 decks)

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