Mapping
Supplemental Instruction
Iowa State University
Leader:
Course:
Instructor:
Date:
Lilli Howard
BIOL/GEN 313
Dr. Vollbrecht
03/10/14
1. What is recombination? What are causes of recombination?
-recombination means that meiosis generates gametes with allelic combinations that
differ from the original gametes inherited by an organism. Recombination may be caused
by the independent assortment of loci on different chromosomes or by a physical crossing
over between two loci on the same chromosome.
2. In a test cross for two genes, what types of gametes are produced with (a) complete
linkage (b) independent assortment (c) incomplete linkage?
a. Nonrecombinant gametes
b. 50% recombinant gametes and 50% nonrecombinant
c. More than 50% nonrecombinant gametes and less than 50% recombinant
3. How would you test to see if two genes were linked?
-do a test cross and look at the ratio of the offspring
-if genes are linked no recombination will occur
-if genes are not linked recombination will occur
4. For single crossovers, why is the frequency of recombinant gametes half the frequency of
crossing over?
-each crossover takes place between only two of the four chromatids of a
homologous pair
5. How does a genetic map differ from a physical map?
-genetic maps are based on rates of recombination; physical maps are based on distances
1060 Hixson-Lied Student Success Center  515-294-6624  sistaff@iastate.edu  http://www.si.iastate.edu
6. In guinea pigs, white coat (w) is recessive to black coat (W) and wavy hair (v) is
recessive to straight hair (V). A breeder crosses a guinea pig that is homozygous for white
coat and wavy hair with a guinea pig that is black with straight hair The F1 are then
crossed with guinea pigs having white coats and wavy hair in a series of testcrosses. The
following progeny are produced from these testcrosses.
a. Black, straight
30
b. Black, wavy
10
c. White, straight
12
d. White, wavy
31
a. Are the genes that determine coat color and hair type assorting independently? Carry out
chi square tests to test your hypothesis.
b. If the genes are not assorting independently, what is recombination frequency between
them?
p. 192
They have not assorted independently
The recombination frequency is 26.5%
7. Waxy endosperm (wx), shrunken endosperm (sh), and yellow seedling (v) are encoded b
three recessive genes in corn that are linked on chromosome 5. A corn plant homozygous
for all three recessive alleles is crossed with a plant homozygous for all the dominant
alleles. The resulting F1 are then crossed with a plant homozygous for the recessive
alleles in a three-point testcross. The progeny of the testcross are:
a. wx sh V
87
b. Wx Sh v
94
c. Wx Sh V
3479
d. wx sh v
3478
e. Wx sh V
1515
f. wx Sh v
1531
g. wx Sh V
292
h. Wx sh v
280
a. Determine the order of these genes on the chromosome.
a. V is the middle gene
b. Calculate the map distances between the genes.
a. WxV = 7 m.u.
Sh  V = 30 m.u.
Wx  Sh = 37 m.u.
1060 Hixson-Lied Student Success Center  515-294-6624  sistaff@iastate.edu  http://www.si.iastate.edu