Download 1 F09 Study Sheet for Quiz #1 Answers to a subset of these

F09 Study Sheet for Quiz #1
Answers to a subset of these problems will be posted by Friday 10/16
Quiz #1 is scheduled for Tuesday Oct 20th and will be worth between 25
and 35 pts.
The quiz will cover:
• All lecture material through 10/11/09
• All information contained in any assignment or handout related to
Mendel Revisited including basic probability, Chi Square analysis,
allele nomenclature, etc
• The first three required extra reading assignments
➔ Please bring your p-value table to use during the quiz. You will be
given the chi square equation.
➔ Also bring to the quiz the handout summarizing possible linkage
relationships between genes
1. Consider this cross:
Parents: Lon (long) males X DpyUnc
Here is how a C. elegans researcher would write out the cross
lon-2 (e678) X
crossed with
dpy-11(e224) unc-42 (e270)V
Define single letter allele symbols for each gene and write out the genotypes of the
parents and the genotypes and phenotypes of the progeny of this cross. All mutant
alleles are recesssive and note that both dpy-11 and unc-42 are on chromosome V.
Be sure to:
• respect conventions concerning allele designations
• use / and ; in the proper context
• indicate the genotype of each gene for each animal
• list both cross and self progeny
• triple-check your work
problem continues on the next page
1
allele symbols:
PARENTS
Lon
X
Dpy Unc

2. A couple discovers that they are both heterozygous for the same two recessive
disease states: cystic fibrosis and progeria (premature aging). The mutated genes
are located on different autosomes.
a. What is the probability that their first child will have one (either cystic fibrosis
or progeria) but not both, of the diseases?
b. Their first kid is has cystic fibrosis, but not progeria. The parents want to
know that probability that she (the kid) is free of the progeria allele -- in other
words is homozygous for the wild-type allele of the progeria gene?
3. After genetic testing using DNA based techniques, a married couple (form a
somewhat inbred population discovers that they are both heterozygous for the same
three recessive autosomal disease states (AaBbCc) The mutated genes are located
on different autosomes.
NOTE: Don’t even think about setting up a Punnet square to work this
problem. Show your work and circle your answer.
a. What is the probability that their first kid is AABBCC?
b. They have a kid and she is phenotypically normal (shows no signs of disease).
The parents want to know that probability she is AABbCc.
4. Your lab partner has collected 48 progeny flies from a cross of two
heterozygous (Aa) parents. All 48 flies show the dominant phenotype She needs
to determine the genotype of each fly and is planning to cross each of the 48
animals with an Aa mate. [ A = dominant wild-type allele a= mutant allele.]
Read through the entire question before writing the answers.
2
a. You are discussing this experiment with your lab partner and suggest that
before she sets up her 48 crosses she consider doing a test cross rather than a cross
with an Aa mate because it will increase the accuracy of her genotyping.
State explicitly what a test cross is and defend your suggestion in one sentence
b. Illustrate your explanation with these calculation:
1. If 4 animals are scored from each cross with an Aa partner, what fraction of Aa
flies will be mis-scored as AA? Show your work here.
2. Do the same calculation (as in #1) with a test cross. Show your work here.
3. Take your answer from 2 and, assuming 4 progeny are scored from each
testcross, indicate how many of the 48 flies will be categorized as AA and how
many as Aa.
5. Recall that one of the goals of the Mendel Revisited Experiment was to
determine if the unc? gene was on the same chromosome as the dpy-11 gene. As
you discovered, assessing linking by scoring progeny ratios in the F2 was dicey
business because the validity of your result rested on the correct scoring of each
animals on the plate and any systematic biases in assessing phenotype led to very
wonky data. C. elegans researchers would get around this problem of assessing
linkage using the following protocol:
1. F2 hermaphrodites that are Dpy but not Unc are picked 1/plate
2. The self progeny of each F2 are scored for the presence of Unc animals and the
genotype at the unc gene inferred
If the unc and dpy genes are assorting independently, what fraction of Dpy nonUnc F2 animals will be heterozygous for the unc mutation? Very briefly
explain your answer.
6 . ESSAY Your mom (who is slightly overweight -- nothing personal here) is an
avid reader of the New York Times. In the Jan 16. 2003 issue she sees the
following article:
From Worm Genes, Human Obesity Clues by Nicholas Wade
“Biologists at MIT have laid a new basis for studying human obesity by
identifying almost all the genes that regulate fat storage and metabolism in a small
animal, the laboratory roundworm.
The finding should provide leads to the many unknown genes that regulate
fat storage in people and to the defects in the genes that underlie many obesity
cases…………..”
3
Your mom is an astute individual, but she is a bit mystified with
respect to the relationship between worms and humans and wonders how the
statement in the second paragraph can be justified. She phones you (or maybe
sends an email) and asks you to explain all of this to her.
Briefly discuss the rationale for studying an organism like C. elegans. In your
essay be sure to include the following:
• explicit definition of a model organism
• two specific advantages of studying a model organism
• an explicit discussion of why what we learn about one organism can often be
applied to understanding a different organism
• Please take time to organize your thoughts before you start writing
7. You have recently isolated a new C.elegans mutant called "piggy"
(pgy-1) which has an extreme dumpy phenotype. You wanted to know if it is
located on the same chromosome as unc-4. First you cross wild-type males with
unc-4 pgy-1 hermaphrodites. All the F1 cross-progeny males are wild-type. These
males are then testcrossed to unc-4 pgy-1 hermaphrodites. You are in a hurry that
day you score the results of the testcross and you only look at 40 cross-progeny
males generated by the test cross.
Phenotype: # of progeney
wild type
Unc Pgy
Unc non-Pgy
Pgy non-Unc
13
11
9
7
a. Designate allele symbols and write out the genotypes of each generation using
the nomenclature for unlinked genes. Be sure to include both self and crossprogeny.
b. Review the definitions of linkage and independent assortment and examine
the summary table at the end of the Mendel Revisited Handout. Your lab
partner says that the data shows that these genes are linked and 40 map units apart.
Write out genotypes using the nomenclature for linked genes. Ignore self-progeny
here.
c. Do you agree with your lab partner’s conlcusion? Do a Chi square analysis of
these data. Show your calculations.
d. What conclusions would you draw from this experiment? Be very explicit
about how you are analyzing the data and what it does or does not tell you. Two or
three sentences here.
4
e. Your advisor suggests that you do another experiment. Briefly propose two
possibilities. One sentence each – I don’t need any detail here. [HINT: One of
these follow-up experiments requires knowledge of the genetic map of C. elegans.
8. REVIEW LINKAGE table at end of Mendel Revisted Handout
Wild-type wasps have a metallic sheen to their body cuticle. Mutant plum strains
have a purplish body color with no metallic sheen. Another mutant strain of the
wasp Nasonia is called rev (reverend) because it looks like it is praying. Wild-type
wasps do not look like they are praying. In Nasonia, 2n=10. Recall that male
wasps are the haploid products of unmated females. In other words, there
phenotypes directly reflect the meiotic output of their parent.
The plum gene is known to be on chromosome 2 (on one end). Your lab
partner is trying to determine the map position for the rev gene. She does the
following crosses (on next page): Phenotypes are indicated. Assume parents are
from true-breeding strains.
Experiment 1 plum
X reverend

F1
all wild-type

F1 females set unmated

Score 100 male progeny
19 wild-type
21 plum reverend
32 reverend (non- plum)
28 plum (non-reverend)
Experiment 2 wild-type
X plum reverend

F1
all wild-type

F1 females set unmated

Score 100 male progeny
18 wild-type
23 plum reverend
30 reverend
29 plum
5
a. Designate allele symbols and write out the genotypes of each generation using
the nomenclature for unlinked genes. Be sure to include both self and crossprogeny.
b. Review the definitions of linkage and independent assortment. Your lab
partner concludes that the reverend gene is on chromosome 2 and 40 map
units away from the plum gene.
• Thoroughly analyze these data and state your response to her conclusion.
Indicate whether you agree or disagree with her conclusion and state why or
why not. Be very explicit
• Outline your analysis clearly and show me all of your calculations.
• Offer your best guess as to what is going on here. and suggest a follow-up
experiment(s) that would support/refulte your conclusions. For the followup experiment, you do not need to suggest specific crosses, but just indicate
in general what need to be done.
χ 2= Σ
Ο −Ε 2
E
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