371B_PS5.html

Genetics 371B, Autumn 1999

Problem set 5 -- based on lectures 24-29

Due Mon Dec. 6 at the start of class

1.
A well-known TV network has a hunch that it's just a matter of time before Teletubbies Go Bad, so they decide to prepare for the inevitable by deciphering Teletubby genetics. They begin a series of shows on Teletubby genetics, and without revealing how they actually managed to do crosses, they announce just the results of the crosses:

Parents F1 F2

Yellow Teletubbies x Blue Teletubbies all Blue Blue, Yellow in 3:1 ratio

Yellow Teletubbies x Red Teletubbies all Red Red, Yellow in 3:1 ratio

Yellow Teletubbies x Purple Teletubbies all Purple Purple, Blue, Red, Yellow in 9:3:3:1

Blue Teletubbies x Red Teletubbies all Purple Purple, Blue, Red, Yellow in 9:3:3:1 ratio

Explain the inheritance of Teletubby color, giving the genotype of each color. Suggest a pathway for Teletubby coloration.

2. A geneticist interested in understanding the regulation of firefly luminescence wants to isolate mutants that are always on (continuously emit light) and mutants that fail to produce light altogether.

(a) Suggest a screen and a selection she could use to identify each class of mutant. (Feel free to be creative -- invent any kind of gadget you like; you just have to spell out the rationale behind the scheme.)

(b) Using your clever schemes, she does succeed in isolating one mutation of each class (i.e., one always-glowing and one never-glowing mutation). Without resorting to any molecular biology or biochemistry, she determines that these mutations represent alleles of two separate genes. What experiment and result allowed her to make this (correct) conclusion? Were the mutant phenotypes dominant or recessive? [Asume that each mutation was available in homozygous form in male and female flies.]

3. A geneticist investigating the synthesis of tryptophan in Kluyveromyces has identified ten trypophan-requiring auxotrophs. Based on complementation analysis, he has determined that the ten mutations fall into 4 complementation groups -- mutations 1, 3, and 5 are in group A, mutations 4 and 7 are in group B, mutations 9 and 10 are in group C, and mutations 2, 6, and 8 are in group D.

(a) Using "+" to represent tryptophan prototrophy and "-" to represent auxotrophy, draw a table to show what the complementation results must have looked like. Your table should show all pairwise crosses between the mutants.

(b)
The geneticist then tests compounds related to tryptophan to see if they rescue growth of the mutants. His results are shown below. Again, "+" means growth and "-" means no growth.

Complementation Group

Supplement A B C D

shikimic acid + - + +

protocatechuic acid - - - +

dihydroshikimic acid - - + +

tryptophan + + + +

What do these results tell you about the functions of the four genes and of the order of action of the genes?

(c)

For each of the following double mutants, indicate which of the four supplements will allow growth and which will not:

(i)

mutation 1, mutation 4

(ii)

mutation 3, mutation 9

(iii)

mutation 7, mutation 8

4. Suppose you have an inkling that a Drosophila gene that is essential for early development also performs an unrelated, non-essential function later on in the adult fly. Outline a strategy that you would use to look at the phenotype of the mutation for this putative second function if the essential developmental function is

(a) as a maternal effect gene

(b) as a zygotic gene

Your strategy need not be detailed, but it should be complete with regard to how you would avoid potentially lethal (developmental) effects of the mutation, and with regard to how you would know you were looking at the secondary mutant phenotype. Assume that you know where the gene maps, and that you have suitable morphological markers if you need them.

5.
A well-kept government secret about the lab accident that created the Incredible Hulk is that a lab mouse was also present in the lab at the time. The mouse showed many of the same phenotypes as the Hulk himself in response to stress (i.e., a cat) it turned big, green and mean. Unlike the human Hulk (who spontaneously returns to normal), once the Hulk state was triggered in the mouse, it remained in the Hulk state and only returned to normal when it was feed some lovely, soothing Velveeta. The original mousy hulk has long since passed away, but not before geneticists established some mousy hulk strains that show all of the traits of the original. Subsequent experimentation has revealed that stress induces transcription of a hulk operon consisting of three genes -- green, mean, and a mystery structural gene X. The three genes are coordinately expressed. Mutations in two regulatory genes m (monster) and am (anti-monster) have the following phenotypes:

[Alleles marked '+' indicate wild type; m1 and m2 are two mutant alleles of gene m; am1 and am2 are two mutant alleles of gene am.]

(a) Propose a model for regulation of hulk gene transcription.

(b) Deletion of the mystery gene X has the phenotype that hulk mice spontaneously return to normal without eating any Velveeta. What do you think the normal protein X does?

2.	A geneticist interested in understanding the regulation of firefly luminescence wants to isolate mutants that are always on (continuously emit light) and mutants that fail to produce light altogether.
	(a)	Suggest a screen and a selection she could use to identify each class of mutant. (Feel free to be creative -- invent any kind of gadget you like; you just have to spell out the rationale behind the scheme.)
	(b)	Using your clever schemes, she does succeed in isolating one mutation of each class (i.e., one always-glowing and one never-glowing mutation). Without resorting to any molecular biology or biochemistry, she determines that these mutations represent alleles of two separate genes. What experiment and result allowed her to make this (correct) conclusion? Were the mutant phenotypes dominant or recessive? [Asume that each mutation was available in homozygous form in male and female flies.]

4.	Suppose you have an inkling that a Drosophila gene that is essential for early development also performs an unrelated, non-essential function later on in the adult fly. Outline a strategy that you would use to look at the phenotype of the mutation for this putative second function if the essential developmental function is
	(a)	as a maternal effect gene
	(b)	as a zygotic gene
	Your strategy need not be detailed, but it should be complete with regard to how you would avoid potentially lethal (developmental) effects of the mutation, and with regard to how you would know you were looking at the secondary mutant phenotype. Assume that you know where the gene maps, and that you have suitable morphological markers if you need them.