Download Quiz 2 Wednesday Answer Key

1. A strain of Saccharomyces cerevisiae that can not survive without arginine and lysine,
is crossed with a strain that can not survive without glutamate. The asci formed by their
diploid progeny were isolated and the following tetrads were counted:
arg+
arg+
argarg-
lys+
lys+
lyslys22
glu+
glu+
gluglu-
arg+
arg+
argarg-
lyslyslys+
lys+
18
glugluglu+
glu+
arg+
arg+
argarg-
lyslyslys+
lys+
328
glu+
glu+
gluglu-
arg+
arg+
argarg-
lys+
lys+
lyslys311
glugluglu+
glu+
arg+
argarg+
arg-
lys+
lyslys+
lys165
glu+
glugluglu+
argarg+
arg+
arg-
lys+
lyslyslys+
154
glu+
gluglu+
glu-
arg+
argarg+
arg-
lys+
lys+
lyslys1
glugluglu+
glu+
arg+
argarg+
arg-
lys+
lyslys+
lys1
glu+
glugluglu+
a) What can you say about the relative positions of the arginine gene and the lysine gene?
Justify your answer.
PD=22+311+165=498
NPD=18+328+154=500
T=2
Very good answer: These genes are unlinked, because PD=NPD>>T
Great answer: Also these genes are on different chromosomes, because T is so small that
there are obviously few cross overs between either gene and centromere. Therefore both
are obviously near centromere, but far from each other, and so on different chroms
b) What can you say about the relative positions of the lysine gene and the glutamate
gene? Justify your answer.
PD=328+311+1=640
NPD=22+18=40
T=165+154+1=320
MU=[0.5*(320)+3*40]/1000=28.0
MU is a better measure than RF, because it incorporates all the double crossovers, not
just those that create NPDs.
2. In the following pedigree, the generation I father is known to be afflicted with an Xlinked dominant trait. Fill in the pedigree to reasonably portray the inheritance of this
disease within the rest of the family. Include an explanation why some individuals are
affected while others are not.
ANSWER: All of the females from generation II should be affected. Half of the
offspring of the GII female daughter should be affected. None of the offspring from
the GII male should be affected.
3. In mice the recessive allele a of one gene causes yellow fur, the recessive allele b of
another gene causes a short tail, the recessive allele c of a third gene causes the mice to
be blind, and the recessive allele d of one last gene causes the mice to dance around their
cage whenever hip-hop is played in the lab, but not rock or country. A line of mice
homozygous for all four alleles has been produced and all four genes have been located
on the long arm of chromosome 3. Several other strains of mice have been identified that
are heterozygous for deletions to large parts of chromosome 3, as follows:
| c|
| d|
|a
|b |
1
2
3
4
5
6
Five crosses were made between a male homozygous for all four recessive traits and a
female heterozygous for one of each of the first five deletions and the following progeny
were produced:
1
2
½ wild type, and ½ blind
½ wild type, and ½ blind, dancing
3
4
5
½ wild type, and ½ yellow fur, dancing
½ wild type, and ½ yellow fur, short tail
All wild type
a) Map the genes to the chromosome sketched above as precisely as you can. Draw lines
showing the limits of the gene’s possible location.
See above, the toughest one is b, as it requires that you understand the wt regions have
none of the genes
b) What phenotypes would you expect in the progeny of an all homozygous recessive
female and a male homozygous for deletion 6?
All dancing