BIO421 Problem Set 1: Due Monday, 14 Oct.
You must show your work for credit
Name_____________________________
1. You are doing a mutational analysis to identify genes involved in leaf formation in the model plant
Arabidopsis thaliana. The mutagen you are using creates 20 new mutated genes in each F1 individual. The
F1 may be self-pollinated to obtain the F2. How many F2 individuals would you have to screen to create
homozygous mutations in every gene in the genome on average one time, given that A. thaliana has a
genome with about 27,000 genes?
The 12 new mutations in each F1 are heterozygous. The likelihood that a new mutation will be homozygous in the F2 is ¼. Therefore, in the F2, 20 x ¼ = 5 homozygous mutations/individual. This is the number of genes screened per F2. 27,000 genes/5 genes per F2 = 5,400 F2 to screen. 2. You have a new mutation that causes a twitching movement in C. elegans, and you suspect it might be a
mutation in the unc-22 gene on chromosome IV. Diagram the complementation test you would do to test
this hypothesis, and describe the results that would indicate that the new mutation is in unc-22.
Here, you will cross your new twitching mutant to an unc-­‐22 mutant and examine the phenotype of the F1 offspring. If the new mutation affects the unc-­‐22 gene, then the F1 will get a mutated allele from both parents and have a mutant phenotype. If we call the new mutation unc-­‐?, then the cross would be: unc-­‐? x unc-­‐22 unc-­‐? unc-­‐22 F1: unc-­‐? unc-­‐22 3. You have a new uncoordinated (unc) mutant in C. elegans. You want to determine which chromosome the
mutation resides on, so you do a two factor cross with dpy-5, a gene in the center of chromosome I. You
cross your new unc mutant strain to a strain with a mutation in dpy-5. Please diagram the cross and indicate
the results that show your new mutation is not on chromosome I.
4. Later on you find that your new unc mutation is on Chromosome V, so you use a two-factor cross to
determine the how far your new unc is from dpy-11. You cross your mutant with a dpy-11 mutant and
isolate a large number of dumpy F2 worms and find the following:
141 F2 dpy produced all non unc F3
54 F2 dpy produced ¼ unc F3
5 F2 dpy were unc as well
How far is the new unc gene from dpy-11?
Draw a map of the chromosome showing the location(s) of the new unc gene.
5. In a two-factor cross between worms homozygous for spe-27 and worms homozygous for unc-22, please
diagram all possible gamete chromosomes that the F1 can produce (ie. non-recombinant and
recombinant), and give the frequency of each chromosome based upon the map position of the two
genes.
spe-27
2.45
unc-22
5.47
6. Two genes, A and B, map next to each other and a similar
distance from a nearby marker gene, C:
You decide to do a 3-factor cross to determine gene order.
for B and C with a strain that is mutant for A:
A B or B A? C You cross a strain that is a double mutant
BC x A
What phenotypes in the F2 progeny would indicate that they contain a recombinant chromosome?
B or C In the example above, you pick F2 that have only the B mutant phenotype. You find that they produce
F3 with the following phenotypes: B, BA, and BC. What is the order of the genes on the chromosome?
You must show your work – draw out the B mutants in the F2 from the two gene arrangements and
decide what F3 phenotypes they will segregate.