Polyteny

Question 1

What is the function of short non-coding RNA?

Answer 1

Silencing

Question 2

What are the two types of RNA?

Answer 2

MiRNA (microRNA) and SiRNA (silencing RNA)

Question 3

What does RISC stand for?

Answer 3

RNA
induced
Silencing
Complex

Question 4

Why are polytonic chromosomes visible under a microscope?

Answer 4

They are so tightly packed and large

Question 5

Would polytonic chromosomes be expressed? Why?

Answer 5

No, they are so tightly coiled that RNA cannot come and transcribe the chromosome (bands cannot be read)

Question 6

What could be a reason for polytonic chromosomes?

Answer 6

Whenever there is a huge metabolic demand, the large presence of chromosomes amplify gene expression of inter-bands.

Question 7

Why do polytonic cells often appear to have a haploid number of chomosomes?

Answer 7

The homologous chromosomes are so tightly paired and aligned

Question 8

What structure connects polytene chromosomes?

Answer 8

The chromocentre

Question 9

What is the puff mechanism?

Answer 9

When flies were exposed to high heat, a polytonic chromosome expanded (puffed) to be expressed more

Question 10

What is the formation of polytene associated with?

Answer 10

The elimination of the mechanism of mitosis after DNA doubling

Question 11

What phase is missing from the polytene cell replication cycle? What phase is the polytene cell “stuck” in?

Answer 11

The M phase is gone, so the cell is in a permanent “interphase”

Question 12

What is intermediate polyteny?

Answer 12

Some phases of the cell are partially or completely bypassed, there may be some stages that occur such as multinucleate chromosomes

Question 13

What chromosomal structures are very present in polytonic chromosomes?

Answer 13

Condensins and coheisins

Question 14

What is a TAD polytonic band?

Answer 14

It is a region of tightly compacted chromatin that forms a visible band

Question 15

What are interbands rich in?

Answer 15

euchromatin

Question 16

What factors contribute to holding sister chromatids and homologous chromosomes togehter?

Answer 16

DNA coiling topological entanglement
Cohesin and Condensins pins
Packing of heterochromatin in dense bands

Question 17

What two processes contribute to small numbers of transcripts needed in very large quantities or certain regions of the chromosome that do not need to replicate as fully?

Answer 17

Gene amplification or underreplication

Question 18

Why are larger puffs directly related to increased transcriptional activity?

Answer 18

Greater accessibility for RNA polymerase enzymes

Question 19

What does CDK stand for?

Answer 19

Cyclin dependent kinase

Question 20

What triggers S and M phase initiation?

Answer 20

CDK activity

Question 21

What type of cyclins and CDK induce S phase?

Answer 21

E or A type cyclins, and CDK2

Question 22

What type of cyclins and CDK induce M phase?

Answer 22

B or A type cyclins and CDK1

Question 23

In endocycling cells, how can we describe CDK activity?

Answer 23

It increases enough to reach the S phase threshold, but not the M phase

Question 24

What does APC stand for?

Answer 24

Anaphase promoting complex

Question 25

If you block the inhibition of APC, what happens?

Answer 25

It downregulates STG, which suppresses CDK1 which would suppress mitosis

Question 26

What are polytonic genes responsible for functionally in fruit fly larvae salivary glands?

Answer 26

They overexpress the production of digestive enzymes like amylase.

Question 27

What does polyteny allow for in giant trophoblasts?

Answer 27

The amplification of genes Growth/metabolic activity Support for placental development and integrity

Question 28

Where is polyteny located in mammals generally? Why?

Answer 28

Mostly in the liver to be able to deal with higher levels of toxic substances

Question 29

What is the mechanism called that protects against cancer? What is it?

Answer 29

Gene compensation is the presence of extra copies of genes that can buffer against loss or mutation of tumor suppressor genes

Question 30

What is polyteny?

Answer 30

When a cell undergoes DNA replication without cell division

Question 31

Why can't thick polytene chromosomes undergo mitosis?

Answer 31

They are so tightly bundled it obstructs alignment/segregation

Question 32

What is somatic synapsis?

Answer 32

Homologous and sister chromatids are synapsed

Question 33

Where is polyteny observed?

Answer 33

In tissues and organs where there is need for rapid development and high levels of function

Question 34

What is a polytene puff?

Answer 34

A site of decondensed chromatin where DNA is accessible for robust transcription