Quiz 3

Genome 371 Spring, 2005
Braun/Pallanck Name: .
Quiz 3
1. You have identified a novel behavioral mutant of Drosophila that bounces around in a jerky fashion
following a gentle tap of the vial containing this mutant. You hypothesize that this mutant (which you
name slamdance, given its phenotype) may represent a model of epilepsy and you proceed to carry out
experiments to map the location of the slamdance gene. You cross a slamdance mutant male to a
female stock that is homozygous for the wild type allele of the slamdance gene. The following number
of progeny with the given phenotypes were obtained from this cross:
247 slamdance females 248 females
254 slamdance males 251 males
(a). (6 points) From this cross what can you say about the dominant/recessive nature of the slamdance
mutation and the possible sex linkage of the slamdance gene? If you do not feel that the data allows
for a definitive conclusion, you should say so. Make sure to justify your answer to this question with
an explanation (please be brief).
The slamdance mutation appears to be dominant because this phenotype is seen in the heterozygous F1
offspring. Because male flies do not transmit their X-chromosome to male offspring and you see the
slamdance phenotype represented in both male and female offspring, this result argues that the
slamdance mutation is not sex linked.
2. From the above cross you managed to narrow down the number of chromosomes that may harbor
the slamdance gene. You now wish to test whether the slamdance mutation is linked to a particular set
of markers designated Ki and Red. You proceed to cross a homozygous (or hemizygous, depending on
your answer to part (a) above) slamdance mutant male that is also homozygous (or hemizygous) for
the recessive alleles of the Ki and Red genes to a female stock that is homozygous for the wild type
allele of slamdance and is also homozygous for the dominant alleles of the Ki and Red genes. The
female progeny are testcrossed and the following number of progeny with the given phenotypes are
obtained:
There were two different versions of this quiz. The version that used the data shown below I will call
A and the other version I will call B
Progeny Phenotypes:
+ + + 23
+ + slamdance 308
Ki + + 97
+ Red + 75
Ki + slamdance 71
+ Red slamdance 89
Ki Red + 316
Ki Red slamdance 21
Using the data above please answer the two questions on the back of this page.

Genome 371 Spring, 2005
Braun/Pallanck Name: .
(a). (10 points) Does the slamdance gene appear to be linked to Ki or Red? If so, draw a genetic map
that shows the arrangement of the Ki and Red genes with respect to the slamdance gene and the map
distance separating the three genes, if possible. Please show your work for full credit.
Answer for version A:
Red
23
Slamdance
19
Ki
Answer for version A:
Red
Slamdance
14
22
Ki
(b). (4 points) Given your answer to (a), would you expect that another marker that is linked to
slamdance, but that maps 40cM away from the slamdance gene would exhibit evidence of linkage to
the Ki or Red markers used in part (a) above? Why or why not?
A marker that maps 40 cM away from slamdance would show linkage to one of the two markers that is
linked to slamdance, but would be more than 50cM away from the other marker that is linked to
slamdance. The maximum amount of recombination that can be observed is 50cM, so markers that are
more than 50cM away from one another would not exhibit evidence of linkage.