This preview shows page 1. Sign up to view the full content.
Unformatted text preview: Cover Page Genetics 380, Spring 2004
Exam III NAME_____________________________________
PAGE Possible Pts. 1 25 2 20 3 20 4 20 5 15 TOTAL 100 TOTAL 100 Points Received Grader Initials Genetics 380, Spring 2003, Name__________________________
E. coli possesses a mechanism called the "SOS response" to cope with various types of DNA
damage. More than 20 SOS genes, which are known to promote the survival of DNA-damaged cells,
are induced by treatments that damage DNA (e.g., UV irradiaton). All the SOS genes share similar
sequences in the regulatory regions called the "SOS box," to which LexA repressor binds to repress
the transcription in the absence of DNA damage. Upon the occurrence of DNA damage, singlestranded DNA produced in the vicinity of DNA damage acts as a signal. A protein called RecA
binds to the single-stranded DNA, and is activated by it. The activated RecA then promotes cleavage
of LexA protein. Once cleaved, LexA no longer represses transcription. Hence, the SOS genes are
allowed to be transcribed. The induced products of the SOS genes then repair the DNA lesions by
various mechanisms, including recombination, excision repair and error-prone repair. Once repaired,
DNA damage signal in the cell decreases and the repression of the SOS genes is restored.
(3 pts) Draw out a linear genetic pathway for the SOS response. Be sure to include the following
components: single stranded DNA, LexA, the SOS box, RecA, the SOS genes, and DNA damage.
Be sure to indicate whether each genetic relationship is stimulatory (
) or inhibitory (
). b. (22 pts) You obtain mutants for various components in the SOS response. You test each mutant for
its ability to respond (i.e., turn on the SOS genes) to DNA damage by UV radiation. In the following
table, fill in whether you would expect high activity (+) or low activity(-) for the regulated SOS gene
for each of the following genotypes in the presence or absence of UV radiation. For each gene,
please note that a “+” indicates the wild-type allele, whereas a “-” indicates a loss-of-function allele.
The first genotype has been done for you as an example.
SOS Gene Activity
recA+ lexA+ SOS box+ SOS gene+ recA- lexA+ SOS box+ SOS gene+ recA+ lexA- SOS box+ SOS gene+ recA+ lexA+ SOS box- SOS gene+ recA+ lexA+ SOS box+ SOS gene- recA+ lexA+ SOS box- SOS gene- recA- lexA+ SOS box- SOS gene+ recA- lexA- SOS box+ SOS gene+ recA+
/ F’ lexA+
lexA+ SOS box+
SOS box- SOS gene+
SOS gene- recA+
/ F’ lexA+
lexA+ SOS boxSOS box+ SOS gene+
SOS gene- recA+
/ F’ lexA+
lexA- SOS box+
SOS box+ SOS gene+
SOS gene- recA+
/ F’ lexAlexA+ SOS box+
SOS box+ SOS gene+
SOS gene- - + Genetics 380, Spring 2003, Name__________________________
2. Page 2 You are characterizing a pattern formation mutant called nanos. You decide to clone the nanos gene.
You map it to a region of the Drosophila third chromosome between the genes pink and radius.
pink nanos radius a. (15 pts) You have two different cosmid clones, one that contains genomic DNA sequences for the
pink gene, and another that contains the DNA sequences for the radius gene. How could you isolate
a genomic DNA clone for the nanos gene? Be sure to describe the reagents that you will need and
the techniques that you will use. b. (5 pts) How would you confirm that the DNA clone that you identify contains the nanos gene? Genetics 380, Spring 2003, Name__________________________ Page 3 3. A circular DNA molecule carries the b-gal gene. You perform single and double digests with the
indicated restriction enzymes, and you run the DNA out on two agarose gels. You stain one of the gels with
ethidium bromide so that you can see all of the DNA bands (panel on the left). You transfer the DNA out of
the other gel onto a filter and perform a Southern blot using sequences for the b-gal gene as your
hybridization probe (the resulting autorad is the panel on the right). The sizes, in kilobases, are indicated for
4.1 1.1 a. PstI
1.6 1.1 EcoRI
0.5 PstI____________ (4 pts) What would the number of sites be if the molecule were linear DNA?
EcoRI__________ c. 1.7
0.5 Southern Blot (4 pts) For each restriction enzyme, indicate how many sites there are on the circular DNA
EcoRI__________ b. EcoRI
PstI PstI____________ (12 pts) Using all of the information from both the ethidium-stained gel and the Southern blot,
draw a map of the circular DNA. Indicate the position of the EcoRI and PstI sites on the circle
below. Indicate the distances between the sites in kilobases (kb). Use a box to indicate the position
of the b-gal gene. Use the additional space and the back of this sheet for scratch work if needed. Plasmid
Map Genetics 380, Spring 2003, Name__________________________ Page 4 5. The hypothetical Grape Fruit Urine Disease (GFUD) causes affected to individuals to have pink
colored urine, but is otherwise harmless. GFUD is mapped to chromosome 22, where there are 5
different RFLPs (named a-e), each with 3 different alleles (named 1-3). The RFLPs are arranged on the
chromosome as follows:
a b c d e Below is a pedigree of a family affected by GFUD. Affected individuals are indicated by the black
squares and circles. All 6 individuals give tissue samples. DNA is extracted, cut with restriction
enzymes for the different RFLPs, and Southern blotted to detect the different RFLP alleles for each
RFLP. The following RFLP allelic data is obtained for each individual (the lines indicate the two
different homologs for chromosome 22 with their corresponding RFLPs): 1 2 a1 b2 c2 d3 e2 a2 b3 c2 d2 e1 a2 b3 c1 d2 e1 a3 b1 c2 d1 e3 3 4 5 6 a1 b2 c2 d3 e2 a1 b2 c2 d3 e2 a2 b3 c1 d2 e1 a1 b2 c2 d3 e2 a2 b3 c2 d2 e3 a3 b1 c2 d2 e1 a3 b3 c2 d2 e1 a3 b1 c2 d1 e3 a. (5 pts) Is GFUD in this family inherited as a sex-linked, autosomal recessive, or autosomal dominant trait? b. (5 pts) Did any of the progeny inherit a recombinant chromosome? If so, then which ones (numbers 3,
4, 5, and/or 6)? c. (5 pts) Which RFLP (a, b, c, d, or e) is most closely linked to the GFUD gene? d. (5 pts) Which allele (1, 2, or 3) predicts inheritance of the GFUD gene? Genetics 380, Spring 2003, Name__________________________ Page 5 d. (12 pts) You decide to clone the GFUD gene, so you build a BAC genomic DNA library and isolate a
set of clones that span this region of chromosome 22. You determine the presence (+) or absence (-) of
each RFLP in each of the 7 BAC clones. Using the map below, put the BAC clones in their correct order
and indicate the location of the markers within them. BAC S has been done for you as an example.
a c d e S + + - - - T - - - + + V + - - - - W - + - - - X - + + - Y - + + - - Z BACs b - - - + - a b c S g. (3 pts) Which BAC is likely to contain the GFUD gene? d e ...
View Full Document
This note was uploaded on 09/29/2011 for the course GENETICS 380 taught by Professor Glodowski during the Spring '08 term at Rutgers.
- Spring '08