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Genetic Analysis of Eukaryotes > Polytene chromosomes > Flashcards

Polytene chromosomes Flashcards

1
Q

What are the 4 reasons why Drosophila are weird?

A

No recombination in males
No recombination on chromosome 4 in either males or females
Females can store sperm for several days
Polytene chromosomes

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2
Q

When do Drosophila use polytene chromosomes? Why?

A

During larval stages in certain cells. Might be an adaptation to increase gene expression

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3
Q

What process creates polytene chromosomes?

A

Endoreduplication

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4
Q

What is endoreduplication?

A

DNA gets replicated and forms two sister chromatids, but cell division doesn’t happen and the chromatids just keep pilling up until there’s thousands of copies

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5
Q

What also happens during endoreduplication that normally only happens in meiosis?

A

Homologous chromosomes synapse

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6
Q

What are polytene chromosomes?

A

Giant synapsed chromosomes

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7
Q

Which two chromosomes will not synapse during endoreduplication?

A

X and Y

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8
Q

What happens near the centromeres to form polytene chromosomes?

A

Centromeres and pericentrometric regions of every single chromosome gets pulled together into the chromocentre

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9
Q

What is the DNA around the centromere like?

A

Tightly packed heterochromatin

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10
Q

What is the centromere lump in polytene chromosomes called?

A

Chromocentre

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11
Q

Is Drosophila chromosome 1 telocentric, metacentric, or acrocentric?

A

Telocentric

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12
Q

Is Drosophila chromosome 2 telocentric, metacentric, or acrocentric?

A

Metacentric

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13
Q

Is Drosophila chromosome 3 telocentric, metacentric, or acrocentric?

A

Metacentric

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14
Q

Is Drosophila chromosome 4 telocentric, metacentric, or acrocentric?

A

Telocentric

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15
Q

How many arms of chromosome 1 stick out of a polytene chromosome?

A

1

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16
Q

How many arms of chromosome 2 stick out of a polytene chromosome?

A

2, the left arm (2L) and right arm (2R)

17
Q

How many arms of chromosome 3 stick out of a polytene chromosome?

A

2, the left arm (3L) and right arm (3R)

18
Q

How many arms of chromosome 4 stick out of a polytene chromosome?

A

Just 1, but chromosome 4 is really tiny so unless we did a really good job with our prep, it won’t show up

19
Q

How is each arm coming out of a polytene chromosome distinguishable from each other?

A

The chromatids stack on each other and each arm has a distinct banding pattern

20
Q

What types of mutations can we easily see with polytene chromosomes?

A

Deletions, translocations, and inversions. Namely large scale chromosome changes

21
Q

How many arms of the Y chromosome stick out of a polytene chromosome?

A

None, it’s mostly heterochromatin and gets lumped into the chromacentre

22
Q

What types of mutations are not very good for looking for with polytene chromosomes?

A

Indels and base pair substitutions

23
Q

How many segments is the Drosophila genome divided into?

A

102

24
Q

How many segments are on the X chromosome? Which ones? How are they arranged?

A

Contains segments 1 to 20. Segment 1 is at the telomere and segment 20 is at the heterochromatin near the centromere

25
Q

How many segments are on chromosome 2? Which ones? How are they arranged?

A

Contains segments 21-40 and 41-60. Segments 21 - 40 are on the left arm, with segment 21 at the telomere and segment 40 at the pericentric heterochromatin. Segments 41 - 60 are on the right arm, with segment 41 at the pericentric heterochromatin and segment 60 at the telomere

26
Q

How many segments are on chromosome 3? Which ones? How are they arranged?

A

Contains segments 61-80 and 81-100. Segments 61 - 80 are on the left arm, with segment 61 at the telomere and segment 80 at the pericentric heterochromatin. Segments 81 - 100 are on the right arm, with segment 81 at the pericentric heterochromatin and segment 100 at the telomere

27
Q

How many segments are on chromosome 4? Which ones?

A

Contains only segments 101 and 102

28
Q

How many segments are on the Y chromosome?

A

None, it’s pretty much all heterochromatin and is in the chromocentre

29
Q

How is each segment divided?

A

Into 6 regions labelled A to F

30
Q

How is each lettered region divided?

A

Each band in the region is numbered

31
Q

How does the systematic nomenclature of polytene chromosomes work?

A

First number is the segment, second is the region letter, third number is the band in the region

32
Q

If we have the name of a specific band on a polytene chromosome, how do we figure out which chromosome it’s on?

A

We can tell the chromosome based on the segment

33
Q

What can you do to find a specific gene sequence on a polytene chromosome?

A

In situ hybridization with a labelled probe complementary to the sequence of interest. It will bind to the complementary sequence on the polytene chromosome on a microscope slide

Genetic Analysis of Eukaryotes (25 decks)

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