Mutations and defects in chromosomal structure

January 2009

Types of Mutations

How do most mutations arise?

A. They are caused by environmental stress and are a response to it

B. They are random events that can be caused by many different things

C. They preprogrammed into the genome to occur in response to specific signals

D. Mutations almost never happen because DNA can repair itself

3

What is a mutation?

A)A change in DNA sequence that causes a change in phenotypeB)A change in DNA sequence that is passed to a cell’s progenyC)Any change in DNA sequence

How do mutations arise?

Experiment: expose bacteria to bactericide; wild type cells do not survive, but there are some colonies on the plates. These colonies have mutations that allow them to grow on bactericide.

How did the mutations arise?

A) Exposure to bactericide causes mutations – creates cells that are resistant.B) Mutations happen randomly – some mutations just happen to make cells resistant to bactericide.

Luria-Delbruck Experiment

What do the results of this experiment mean?

A) Mutations are more frequent when cells are exposed to bactericideB) Mutations likely occurred after exposure to the bactericideC) Mutations likely occurred before exposure to the bactericide

Random mutations likely occurred before the cells were exposed to bactericide.Some cells acquired mutations that allowed them to grow on bactericide.

If depurination occurs 1000 times/hour in humans, whydon’t humans have more genetic diseases (mutations)?

A) most of the mutations are in parts of the genome that are not transcribedto mRNA, so the mutations have little effect.B) most depurinations are fixed by DNA repair enzymes.C) most depurinations will occur in cells that are not part of the germline, so theywill not cause disease.D) the redundancy of the genetic code will prevent the depurinations from changingthe protein sequence and causing disease.

Which type of mutation is most likely to lead to the formation of a nonfunctional protein?

A)A silent mutationB)A frame shift mutationC)A missense mutationD)All of the above will lead to nonfunctional proteins

A type of human dwarfism results from the production of mutant SHR-1 protein. You look at the length of the mutant SHR-1 and the normal (wild-type) SHR-1 protein, and discover that the mutant SHR-1 protein has fewer amino acids.

What do you expect to find when you examine the DNA sequence?

A. nucleotides were deleted B. additional nucleotides were added C. one nucleotide was changedD. without additional information, any of the above are possible

You are studying a gene called Ant-1. You discover an insertion of one nucleotide in a mutant Ant-1 gene. When you compare the wild-type Ant-1 protein and the mutant Ant-1 protein, you expect that:

A. The wild-type Ant1 protein will be longer than the mutant Ant-1 protein

B. The mutant Ant-1 protein will be longer than the wild-type Ant 1 protein

C. The wild-type Ant-1 protein and the mutant Ant-1 protein will be the same length

D. Answer A and B

E. All of the above

The following DNA sequence corresponds to the two extreme ends of a gene’s coding regions:

5’ ATG-GAA//CAG-TGA 3’ Each codon is separated by a dash and the middle of the gene is represented by “//”.

Referring to the codons listed above, which of the following sequence changes is likely to interfere most with the function of this gene?

A. 5’ ATG-GAA//CAA-TGA 3’B. 5’ ATG-TAA//CAG-TGA 3’C. 5’ ATG-GAG//CAG-TGA 3’D. (a.) and (b.) are equally likely to interfere with the function of this geneE. (b.) and (c.) are equally likely to interfere with the function of this gene

ATG= Met GAG= Glu TGA =Stop

GAA= GluTAA= Stop

CAA= Gln CAG = Gln

You have isolated a conditional mutation in Neurospora that has the following phenotype: At 30 degrees it can synthesize DNA, at 42 degrees no DNA is synthesized and the cells die. This mutation is most likely a

a. Nonsense mutationb. Missense mutationc. Frameshift mutation

Let’s say you lived in a world where there was no physical (UV light and X-ray), and no chemical mutagens. Would your DNA undergo mutations?

A. Yes

B. No

You heard on the news that grilling steak can create carcinogens and cause cancer, so you decide to test the hypothesis with the Ames Test

- control no sample

+ controlsodium azidea known carcinogen

experimental –small piece of grilled steak

Are the colonies on the experimental plate likely to be revertants?A) yesB) no

You heard on the news that grilling steak can create carcinogens and cause cancer, so you decide to test the hypothesis with the Ames Test

- control no sample

+ controlsodium azidea known carcinogen

experimental –small piece of grilled steak

Are the colonies on the negative control plate likely to be revertants?A) yesB) no

Test substance + rat liver enzyme + distilled water 500Test substance + distilled water 2distilled water 10rat liver enzymes 1positive control 675negative control 12

The test substance is:A) a mutagenB) a mutagen, but only when metabolizedC) not a mutagenD) can’t tell – there is contamination in the experiment

C A T C G

G T A G C

Depurination C A T C G

G T A C

apurinic site

Depurination is the removal of a purine base.After a depurination, how many (of the 4) replicated DNA strandsare likely to be mutant?

A) 1B) 2C) 3D) 4

C A T C G

G T A G C

C A T X G

G T A C

When the mutation 21 is present, wild type protein no longer functions.

This can explain the following mode of inheritance

A.dominant (Aa or AA = disease)

B.recessive (aa = disease)

Characterization of Mutants (complementation)

You study eye formation using Mexican cave-dwelling blind fish. You know that blindness is a trait controlled by multiple genes and inherited in a recessive manner.

A blind fish from a true-breeding line in one cave was crossed to a blind fish from a true-breeding line in another cave. If the mutation that cause blindness is in the same gene in two fish, you should see

A. None of the offspring are blindB. 25% of the offspring are blindC. 50% of the offspring are blindD. 75% of the offspring are blindE. All of the offspring are blind

Study publishedJan 8, 2008Current Biology Journal

1 2 3

1 + +

2 + -

3 + -

You isolate 3 mutant strains of rII, labeled 1-3. You coinfect E. coli K12 with pairwise combinations (1&2, 1&3 etc.) of the 3 mutant strains and get the following results:

How many genes did you mutate?

A. 0

B. 1

C. 2

D. 3

E. 4

1 2 3 4

1 + + +

2 + - -

3 + - -

4 + - -

Oops, you just found another rII mutant strain on your laboratory bench. So you expand your complementation test to include the 4 mutant strains and get the following results:

How many genes did you mutate?

A. 0

B. 1

C. 2

D. 3

E. 4

Complementation DataNeurospora Auxotrophs (Haploids) Mated with Each Other and

Plated on Minimal Plates

1 2 3 4 5 6

1 - + - - + +2 - + + + +3 - - + +4 - + +5 - +6 -Strains 1-6 are all arg- auxotrophs, how many genes?

A. 1B. 2C. 3D. 4E. 5

CSU has hired you to generate green ram mascots. You mutate a bunch of rams and get 4 that are green because of recessive mutations. You carry out crosses between all the rams (all rams can mate with each other, don’t worry about mascot sex) and produce the following results where a "-" means mutant green rams were produced and a "+" means wild-type white rams were produced.

1 2 3 4

1 + ? -

2 - +

3 +

4

Which statement is correct?

1. 1 crossed with 3 will produce a green ram

2. 1 crossed with 3 will produce a white ram

UNC has hired you to generate gold bear mascots. You mutate a bunch of bears and get 4 that are gold because of recessive mutations. You carry out crosses between all the bears (all bears can mate with each other, don’t worry about mascot sex) and produce the following results where a "-" means mutant gold bears were produced and a "+" means wild-type brown bears were produced.

1 2 3 4

1 - + ?

2 + -

3 +

4

Which statement is correct?

1. 1 crossed with 4 will produce a gold bear

2. 1 crossed with 4 will produce a brown bear

phage assembly pathway

Next, you want to determinehow many different genes yourmutants represent, so you performa complementation test.

Which is/are true in your complementation test?A) if the mutations of the parents are in the same gene,plaques will not form.B) If the mutations of the parents are in the same gene,plaques will form.C) if the mutations of the parents are in different genes,plaques will form.D) Both A and C are true.E) Both B and C are true.

Complementation Test Results

1 - + - + + +

2 - + + + -

3 - + + +

4 - + +

5 - +

6 -

1 2 3 4 5 6

How many different genes do your 6 mutants represent?A) 6 C) 4B) 5 D) 3

Complementation data can be presented in a grid:

How many complementation groups are there?A. 1 B. 2 C. 3 D. 4 E. 5

1 2 3 4 5 6

1 - - + - - + +

2 - - + + + +

3 - - - + +

4 - - + +

5 - - -

6 - -

Here’s a grid for six strains showing the same mutant

phenotype:

Chromosomal Structure Mutations

(Translocations, inversions, and duplications)

Which color signals would represent balanced gametes produced by meiosisof the above translocated chromosomes?

A) gamete 1: orange, (red and green) gamete 2: (orange and green), redB) gamete1: orange, red gamete 2: (orange and green), (green and red)C) gamete 1: red, (red and green) gamete 2: (orange and green), orange

Chromosome arrangement of the female translocation carrier

Metaphase of meiosis I (homologues segregate)