Problem Set 8, Fall 2015
Name:
8 points total
1. The mythical Antarctic toad is found in several true breeding strains. One has blue skin and long toes.
The second has red eyes. You cross blue-skinned, long toed X red eyed and find the progeny all have all
wild type phenotypes (i.e. not blue skinned, long toed or red eyed). You test cross these F1’s and find the
results shown below. Only the recessive phenotypes are listed below
123
4513
118
19
125
4781
21
134
9834
long toed, blue skinned, red eyed
long toed, blue skinned
blue skinned, red eyed
long toed, red eyed
long toed
red eyed
blue skinned
wild type
a. What do the results shown above say about the chromosomal location of the three genes?
b. Please calculate the genetic distance between the l and b genes, i.e. the genes that produce long
toes and blue skin.
c. There are three linked genes, a, b and c. a and b are 10 map units apart and b and c are 20 map
units apart and a and c are 30 map units apart.. If you cross a b c/+ + + X the triple recessive, what
fraction of the progeny will be phenotypically a- (i.e. homozygous a-) and b- but wild type for c?
(hint: the probability of doubles = the product of the probability of singles)
2. Several strains of the seabass C. zengae, have accumulated extensive rearrangements of chromosome 2,
as shown below.
original chromosome
strain I
strain II
strain III
Determine the order in which the changes had occurred and name the type of rearrangement.
(note: each new strain resulted from a single rearrangement in its parent.)
1
Problem Set 8, Fall 2015
8 points total
Name:
3. Name the chromosomal anomaly present for each pair of chromosomes (the wild type chromosome is
the uppermost chromosome of each pair, also indicated by the star). Also, show the chromosomes as they
would appear synapsed in meiosis I, including letters and centromeres.
a.
b.
4. You map two genes, bl, which causes blue fur and grn, which causes green teeth, and find that they are
21 mu apart. Starting with another pair of parents (one heterozygous and the second homozygous
recessive) you find the following results:
817
793
37
42
blue fur, green teeth
wild type
blue fur, normal teeth
normal fur, green teeth
Calculate the apparent map distance between the genes. How can you explain this outcome?
2
Problem Set 8, Fall 2015
Name:
8 points total
5. In studying a particular animal, you find that some of the chromosomes appear a bit unusual. The
relevant chromosomes are shown below. One pair of homologues is on the left and the second pair is
shown on the right. For each pair, the normal chromosome is the one on top.
a. What is the name of the chromosomal alteration that generated the abnormal chromosomes?
b. Show the chromosomes synapsed in meiosis. Please include the genes.
c. You find an individual homozygous for the abnormal chromosomes as shown below. Show this
individual's chromosomes synapsed in meiosis. Please include the genes.
3
Problem Set 8, Fall 2015
Name:
8 points total
6a. A woman with Turner syndrome (XO) is found to be color-blind. Both her mother and father have
normal vision. How can her colorblindness be explained? Did the nondisjunction occur in the father or
mother?
b. A man with Klinefelter syndrome (XXY) is found to be color-blind. Both his mother and father have
normal vision. How can his colorblindness be explained? Did the nondisjunction occur in the father or
mother?
7. While looking at a large number of siblings that are all homozygous wild type for the prpl gene (which
causes purple blotches when homozygous mutant), you find that each individual has a different pattern of
purple blotches on their skin. How might you explain this result, assuming that it results from an effect on
the prpl gene?
8. Strains heterozygous for each of six Drosophila mutations, a – f, and for each of six different deletions,
1 – 6 are generated. The table below shows whether such strains displayed wild type (+) or mutant (-)
phenotypes. The figure illustrates the region deleted in each deletion strain (region deleted indicated by a
bar) as determined by cytological examination of polytene chromosomes.
a
b
c
d
e
f
del 1 +
–
+
+
+
–
del 2 +
–
+
+
–
–
del 3 –
+
–
+
+
–
del 4 –
+
–
–
+
+
del 5 –
+
–
+
+
+
del 6 –
–
–
+
+
–
Assign each recessive mutation to the relvant region of the chromosome.
4