Department of Biological and
Environmental Sciences
BIO L320 – Genetics Lab
Dr. Jacqueline Jones
Lab 6. Chromosome Linkage Mapping
You have conducted some pioneering work in mapping the chromosomes of Martians.
Martians show the WZ sex-determining mechanism, so you obtain the data in Table 1. By
conducting test crosses of double heterozygous members of sex A with hemi-zygous recessive
members of sex B for four Z-linked recessive traits in Martians: blue feet (bl) [recessive to wildtype green feet], bobbles on the head (bo) recessive to wild-type ridges on the head], five toes
(ft) [recessive to the wild-type four toes], and warty-nose (wn) [recessive to wild-type normal
nose].
Table 1. Recombinant proportions for four Z-linked gene pairs in Martians.
Gene pairs
# recombinants/total offspring
Blue feet (bl) – bobbles (bo)
536/12,382
Blue feet (bl) – five toes (ft)
2026/6611
Blue feet (bl) – warty nose (wn)
1644/4646
Bobbles (bo) – five toes (ft)
105/409
Bobbles (bo) – warty nose (wn)
1415/4515
Five toes (ft) – warty nose (wn)
28/537
Frequency
% = cM
1. What sex would members of sex A have been? (1 point)
2. What sex would members of sex B have been? (1 point)
3. What are the distances between each of the gene pairs in Table 1 in centrimorgans (cM)?
(9 points, ½ each for frequencies and 1 each for distances in cM)
4. What are the relative orders of these genes on the Martian Z chromosomes? (4 points)
5. Construct a linkage map of the Martian Z chromosome below showing the relative
locations of these genes along it with relative locations in centrimorgans (cM) (5 points).
Total = 20 points.
Department of Biological and
Environmental Sciences
BIO L320 – Genetics Lab
Dr. Jacqueline Jones
Lab 6. Restriction site mapping of a mitochondrial DNA molecule
You have isolated some mitochondrial DNA (mtDNA) from walleye (Sander vitreus).
The mtDNA was digested with four restriction endonucleases Apa I, Bcl II, Cla I, and Dra I).
The fragments obtained (sizes in kilobase pairs) with each enzyme were as follows:
Apa I 11.5, 3.0, 2.0
Bcl II 1 cut only – fragment size 16.5
Cla I 11.3, 5.2
Dra I 13.0, 3.5
You wish to map these restriction sites on the molecule, so you conduct a series of double
digests, which give the following sized fragments:
Apa I/Bcl II
10.0, 3.0, 2.0, 1.5
Apa I/Cla I
7.5, 4.0, 2.0, 1.8. 1.2
Apa I/Dra I
9.5, 3.0, 2.0, 1.5, 0.5
Bcl II/Cla I
6.0, 5.3, 5.2
Bcl II/Dra I
13.0, 3.0, 0.5
Cla I/Dra I
5.5, 5.2, 3.5, 2.3
Draw a linear restriction site map for this Daphnia mtDNA that is opened at the single
Bcl II restriction site. Show your working, including alternative positions of restriction sites in
the preliminary maps.
A polymorphism is now found using Dra I such that the new fragment pattern for this
enzyme becomes: 8.0, 5.0, 3.5. What has happened?
You conduct two more double digests in order to map this variable site, giving results as
follows:
Cla I/Dra I
5.2, 5.0, 3.5, 2.3, 0.5
Apa I/Dra I
5.0, 4.5 3.0, 2.0, 1.5, 0.5
Map the variable site and mark it with an *.
You examine another individual with Dra I revealing the following fragment results: 9.0,
5.0, 3.5. You think that this is a bit odd. So you conduct a few more digests, getting the
following results:
Apa I 11.5, 4.0, 2.0
Cla I 11.3, 6.2
Where is this phenomenon affecting the mtDNA molecule? Indicate the portion of the
molecule that is affected. What fragments would you expect to result from a Cla I/Dra I double
digest on this individual?
Draw a picture of a gel showing all of the fragments obtained in the above digests.
Total points = 50
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