Lab Exam 2

Question 1

What pigments are required for wild type eye colour?

Answer 1

All of them:
no mutations
Pteridine AND ommochroome pigments

Question 2

What pigments and mutations cause the brown eye colour?

Answer 2

Brown gene mutation inhibits Pteridine pathway:
only ommochrome pigment

Question 3

What pigments and mutations cause the white eye colour?

Answer 3

No pigments are present because,
a mutation in the white gene impairs the transport of both precursor molecules
therefore both the pteridine pathway and the ommochrome pathway are inhibited

Question 4

What pigments and mutations cause the scarlet eye colour?

Answer 4

Scarlet gene mutation inhibits the ommochrome pathway
so all the pigments of the pteridine pathway create this eye colour

Question 5

What pigments and mutations cause the sepia eye colour?

Answer 5

Only the drosopterin pigment is absent
the mutation takes place in the specific area of the pigment in the pteridine pathway

Question 6

How are the Pteridine pigments arranged in order of migration on the chromatogram?

Answer 6

Top:
yellow (Isosepiaterin and Sepiapterin)
Blue (Biopterin and 2-amino-4-hydroxypteridine)
Green-blue (Xanthopterin)
Violet-blue (Isoxanthopterin)
Orange (Drosopterins)
Bottom:

You Better Go Vote Opposition

Question 7

What is the order of epistatic hierarchy for eye colour?

Answer 7

(1) Wild-type
(2) White
(3) Scarlet
(4) Brown
(5) Sepia

Question 8

What is an alternative way to have white-eyed offspring, other than a mutation in the white gene?

Answer 8

White eyes can also result by crossing brown and scarlet eyed flies
(when both mutant alleles are present)

Question 9

What are the two main reasons the observed segregation does not match those predicted based on Mendel’s Laws?

Answer 9

(1) the differences are due to random chance alone
(2) the initial assumption to calculate the expected frequencies is invalid

Question 10

What is the X^2 formula?

Answer 10

First find the observed and then the expected values (punnet square)
Then do the formula for each and add together
find the Critical value and compare to the calculated X^2

Question 11

How do you interpret the results of a chi-squared test?

Answer 11

Degrees of freedom (df) = # of phenotypic classes - 1
oc= 0.05

If the calculated X^2 value is larger than the value from the table, then you reject the null hypothesis

Question 12

Can you see the difference between wild-type and scarlet flies on the chromatography plate?

Answer 12

No, because this test does not show the ommochrome pigment
Both eye colours contain all the pigments of the pteridine pathway and so they appear the same

Question 13

Can you see the difference between brown and white eyed flies on the chromatography plate?

Answer 13

No, both of the colours lack all the pigments of the pteridine pathway

Question 14

How do you tell the difference between sepia and scarlet on the chromatography plate?

Answer 14

Sepia lacks the drosopteria pigment while scarlet has all the pteridine pathway pigments

Question 15

The highest observed phenotype is the _________ recombinant and the lowest is the _______ recombinant. The remaining are ________ recombinant.

Answer 15

The highest observed phenotype is the PARENTAL recombinant and the lowest is the DOUBLE recombinant. The remaining are SINGLE recombinant.

Question 16

How do you determine gene order of a trihybrid cross?

Answer 16

The two alleles that remain the same as in the parental recombinants in the double recombinant genotype are on the outside. The gene that changes from the parental is in the middle.

Question 17

How do you calculate genetic distance?

Answer 17

(1) First two genes in the order: add the amounts everytime they differ from parental then divide by total and times by 100
(2) Do the same for the middle and last gene in the order
(3) now do this for the first and last but, add the double recombinant numbers multiplied by two

Question 18

How do you determine the Coincidence and Interference?

Answer 18

Question 19

In the white-1
mutation (w), the transcription is disrupted,
and the white protein is not produced. Hence,
because white does not partner with brown and
scarlet, the eye cells are unable to uptake
pigment precursors, causing the white-eye
phenotype (absence of pigmentation).

How does this occur?

Answer 19

Further molecular studies on the white-1 mutation
indicated that an insertion of a Doc-retroposon
(4,700 bp) in the promoter region resulted in its
inactivation, and thus, the disruption of
transcription.

Question 20

What is the Polymerase Chain Reaction (PCR) test?

Answer 20

a unique molecular biology technique to make
multiple copies of a desired piece of double
stranded DNA in a test tube. This technique is
known as the Polymerase Chain Reaction and is
based on the natural process of DNA
replication.

Question 21

What are the three main steps of a PCR test?

Answer 21

Denaturation, annealing, and extension

Question 22

What does the process of PCR look like?

Answer 22

Question 23

How is the DNA of wild-type and mutant flies determined through PCR?

Answer 23

specific primers bind to the promoter region on both, wild type and mutant flies

For instance, the combination of primer 1 and primer 3 are specific to the wild-type and will produce a 467 bp DNA fragment (active w+ allele). The combination of primer 2 and primer 3 will produce a 704 bp fragment specific to the doc-retroposon (non-active allele).

Question 24

What is DNA gel electrophorasis?

Answer 24

the separation of molecules based on their size using their attraction to an electrical charge

Note that DNA is negatively charged due to phosphate groups

Question 25

Review the last lab