## Transcribed Text

You are tracking three loci in the fruit fly, loci in A, B, and C, and want to know
whether the loci are linked and if so what their physical distances are from one
another as well as the physical order they are in. To find out this information you
perform a three-point testcross with a fly that is heterozygous for all three
alleles. The progeny of this cross are:
Genotype
Number of
individuals
a/a
389
•
B/b
•
C/c
A/a
410
•
b/b
•
c/c
a/a
39
•
b/b
•
C/c
A/a
44
•
B/b
•
c/c
a/a
77
•
b/b
•
c/c
A/a
83
•
B/b
•
C/c
a/a
6
•
B/b
•
c/c
A/a
5
•
b/b
•
C/c
TOTAL
1053
(a) What is the recombination frequency between loci A and B?
(b) What is the recombination frequency between loci B and C?
(c) What is the recombination frequency between loci A and C?
(d) Are these loci linked?
(e) Demonstrate the physical arrangement of the genes on the chromosome, i.e.
the order of the genes on a chromsosome as well as their map distances.
(f) Write out the genotypes of the parents for this cross, indicating which
allelesare linked with one another for each parent?
X
Question 2
In a transformation experiment, DNA of a p+q+ strain was used to transform a
recipient strain that is auxotrophic for these markers. The number of each class
of transformants is shown below:
Cla
Genoty
Numb
SS
pe
er
1
p+q+
405
2
p+q-
300
3
p-q+
195
a) If the total number of transformants isolated was 900, what is the co-
transformation frequency for the pandg loci?
b) Diagram how each class of transformants were obtained starting with
the recipient auxotroph. You should include one diagram of the recipient
auxtroph, one diagram of the event that led to class 1, one diagram of the
event that led to class 2, and one diagram of the event that led to class 3

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Question 1

Recombination frequency is a measure of genetic linkage. It's the frequency of a single chromosomal crossover (sometimes called crossing over - two parts of genetic material on homologous chromosomes swap places during meiosis – literally „cross over“ to the other homologous chromosome; the resulting chromosomes are called recombinant chromosomes). A cM – centiMorgan (in honour of geneticist Thomas Hunt Morgan) – is a unit that describes a recombination frequency of 1%. Its parent unit, the Morgan, is rarely used (1 Morgan = 100 cM). For instance...