Problem 1
You are mapping 5 genes relative to one another in order to determine their linkage relationships
and map distances between them. The genes are A, B, C, D, and E, with dominant alleles A, B, C, D, and
E and recessive alleles, a, b, c, d, e.
You have been given data from a previous student in the lab you are working in that indicates that
genes D and E assort independently of one another, in that mapping these two genes showed a
recombination frequency of 50% (50 map units).
The stocks that you have available to you are * indicates that you do not know if the genes are on the
same chromosome or not:
1)
2)
3)
4)
A/A * B/B * C/C * D/D * E/E
a/a * b/b * C/C * d/d * E/E
a/a * B/B * c/c * D/D * e/e
a/a * b/b * c/c * d/d * e/e (TESTER STOCK)
A) You do a cross of stock #1 with stock #2
What is the genotype of the F1?
B) You cross the F1 from cross A to stock #4. This allows you to deduce the relative proportions of
gametic genotypes produced by F1 individuals. Why did you do the cross to stock #4?
Based on 1000 test cross progeny phenotypes, you deduce that F gametes were produced in the
following numbers:
316
314
31
39
130
140
17
13
A*B*C*D*E
a*b*C*d*E
A*B*C*d*E
a*b*C*D*E
A*b*C*d*E
a*B*C*D*E
A*b*C*D*E
a*B*C*d*E
C) You do a second cross of stock #1 with stock #3
You take the F1 from this cross (what is the genotype of this F1?) and cross F1 individuals to stock
#4. Again you deduce the F1 gametic genotypes based on progeny phenotypes. Based on 1000 test
cross progeny phenotypes, you deduce that F gametes were produced in the following numbers:
243
237
62
58
155
165
46
34
A*B*C*D*E
a*B*c*D*e
A*B*c*D*e
a*B*C*D*E
A*B*C*D*e
a*B*c*D*E
a*B*C*D*e
A*B*c*D*E
1) Are the genes linked on the same chromosome? Draw a chromosomal map of these genes, showing
the distances in map units when possible.
2) Is there evidence of interference?
Your group may be asked to stand up and present your solution to the class, using the board and
providing a clear explanation of how you solved this.
Problem 2
Write a coherent essay on the evidence that established that DNA is the
genetic material. You may use figures in your essay. You may be asked
to get up and present to the class, using the board, a clear explanation of
this evidence.
Problem 3
Write a coherent essay on the evidence that established that single
genes often encode single polypeptide chains. You may be asked to get
up and present to the class, using the board, a clear explanation of this
evidence.
Problem 4
Write a coherent essay on the evidence that established that the gene is
a linear structure, not a single base pair of DNA. Include in your essay
why the term cistron was an appropriate term for a gene? You may be
asked to get up and present to the class, using the board, a clear
explanation of this evidence.