Test2: Lect 8 Mary Logan

Question 1

Fly chromosomes:

• Name chromosomes?
• Which chromosome has the most genes on it?
• Which is smallest?

Answer 1

• Name chromosomes?
  1: 2 sex chromosomes
  2: 2nd, 3rd, and 4th chromosome.
  3: Total of 4 chromosomes
• Which chromosome has the most genes on it?
  Chromosome 3
• Which is smallest?
  Chromosome 4 is tiny

Question 2

Endoreplication:

• Define:
• How does it apply to flies?

Answer 2

• Define:
  Replication of DNA without cellular division
• How does it apply to flies?
  Some cell types in flies just grow larger and undergo endoreplication.

Question 3

What makes male flies weird during meiosis?

Answer 3

The males don’t do meiosis.

Question 4

What does endoreplication lead to in flies?

In what tissues usually?

Answer 4

What does endoreplication lead to in flies?
Polytene chromosomes (chromosomes which through endoreplication have increased copy number, but are all connected to the same chromosome)
In what tissues usually?
Salivary glands

Question 5

Drosophila genes are named after the mutant phenotype.

- Give examples!!

Answer 5

• Give examples!!
  1: Ebony, a gene, a mutant recessive genotype will produce a black fly
  2: White, a gene, a mutant recessive genotype will produce a white eyed fly
  3: Curly, a gene, a mutant dominant genotype will produce a fly with curled wings

Question 6

What is a chemical mutagen which is still used on drosophila for the generation of random mutations today?
What type of mutations does it form?

Answer 6

EMS.

Single point mutations

Question 7

Five classes of genetic mutations:

Answer 7

Null allele (abolish gene function)
Hypomorph (partial loss of function)
Neomorph (gain of function, or expressed in new tissue types)
Hypermorph (too much gene product)
Antimorph (antagonizes wildtype gene function, dominant negative)

Question 8

• null allleles:

Answer 8

completely abolish the gene function (e.g. a deletion)

m/m = m/Df

Question 9

• hypomorph:

Answer 9

partial loss of the function (e.g. reduced transcription levels
OR mutation inhibits protein function OR increased turnover)
m/m < m/Df

Question 10

• neomorph (gain-of function):

Answer 10

acquire a new function or are misexpressed

in a new tissue or at the wrong time (e.g. Inversions-fusion protein)

Question 11

• hypermorph:

Answer 11

too much gene product (e.g duplications)

m/m > m/+ > m/Df

Question 12

• antimorph:

Answer 12

(dominant negative) antagonizes wild type function
m/+ > m/Dp (duplication)
m/+ <= m/Df

Question 13

How could you use complementation testing to identify phenotype?

Answer 13

Cross mutant with another mutant of the gene (deficiency would work). If offspring are not possible, they compliment, this is the same gene.

Question 14

3 important traits of balancer chromosomes:

Answer 14

1: multiple inversions – caused by X-­‐ray irradiation (inversions mean it will not recombine)
2: carry dominant and recessive mutations (dominant is easily visible, the recessive is lethal)
3: homozygous lethal (or sterile)

Question 15

Describe an EMS screen if mutant is dominant:

Answer 15

EMS given to male, some gametes mutated ->
Male has children ->
Some children have the phenotype! AMAZING YOU DID IT!

Question 16

Describe an EMS screen if mutant is recessive:

Answer 16

CyO = curly wings. Dominant mutation. Homozygous lethal, in this case, it is on the balancer chromosome.

Sco = scutoid, it is on the other normal chromosome in virgin females. Dominant mutation, homozygous lethal

Step 1: EMS given to male, some gametes mutated ->
Progeny are either +/+ or some type of m/+ (where m is a mutation, hopefully the one you want)
Step 2: cross your +/+ or +/m progeny with virgins of CyO / Sco ->
Throw out all progeny with Sco. ->
The rest are either +/Cyo or m/Cyo
Step 3: cross +/Cyo or m/Cyo with CyO/Sco virgins ->
Collect all flies that are Cyo only. These are either CyO/m or Cyo/x. Collect these in large stocks so you have the brothers and sisters together
Step 4: inbreed your collected stocks. The CyO/m will give 1/4 prob of m/m, which you can collect to breed.
Step 5: Compliment test the different strains you found with a mutation of interest. Those which fail to compliment, aka you cross them and the phenotype is still there, are likely mutations in the same genes.
Those that compliment are different genes.

Question 17

If mutants compliment they are likely mutated in ________ genes?

Answer 17

Compliment means no phenotype
Different genes
they got each others back!

Question 18

You’ve done your EMS screen, you have your mutant, how do you find out where your mutation is?``

Answer 18

Recombination mapping (with known mutations)
Screen with deficiencies (m/Df), note, this uses balances chromosomes too.
Sequence the genome.

Question 19

You’ve found your mutant gene, or so you think… how can you test to see if your right?

Answer 19

1: PCR the gene
2: RNAi, see if you can inhibit gene product to reproduce phenotype
3: rescue the gene, put an intact copy of the gene into the fly, it should revert to normal

Question 20

You found your mutant recessive fly, why would you do an EMS screen again?!?
- Two types?

Answer 20

To find mutations which either return your mutant to normal, or worsen the condition further.
- Two types?
Enhancer screens: looking for worsening phenotype
Suppressor screens: looking for mutations which improve your mutant back to wild type

Question 21

In a suppressor screen you find a mutation in another gene which changes your phenotype. How is this gene and your other gene likely related?

Answer 21

You observe a weaker phenotype when an interacting mutated gene is inhibitory

Question 22

In a enhancer screen you find a mutation in another gene which changes your phenotype. How is this gene and your other gene likely related?

Answer 22

sometimes observe a stronger phenotype when two genes in the same pathway are affected
(the genes may be in the same pathway)

Question 23

Deficiency kits:

Answer 23

Regions missing part of the chromosome