1
Ecology’335,’
Evolutionary Biology
,’2013 ’
Exercise’ 3.’Due’Feb’4
’ at’11’am. ’
Multilocus genotypes, linkage, genetic drift and mutation rate.
1.
For 20 loci each with 2 alleles each:
a.
How many
haplotypes
(gamete types, sperm or eggs) are possible?
1,048,576 gamete types are possible. This is as simple as raising 2 to the 20
th
power.
b.
How many
diploid
genotypes (zygotes) are possible?
3,486,784,401 genotypes are possible. Remember that there are three possible
genotypes for each locus (two homozygous, one heterozygote), and there are 20 loci.
So raise 3 to the 20
th
power.
2.
You cross an
abC
haploid genotype with an
ABc
haploid genotype and obtain the
following haploid progeny:
ABC ABc
AbC
Abc
aBC
aBc
abC
abc
0
100
0
100
100
0
0
100
a.
Are
A
and
B
loci in linkage equilibrium with each other (show your work)?
Yes:
A and B, A and b, a and B and a and b occur in equal frequencies
OR you can
plug in the equation for LD:
LD = Freq (AB) x Freq (ab) – Freq (Ab) x Freq (aB) =
(0.25 x 0.25)  (0.25 x 0.25) = 0
b.
Are
A
and
C
loci in linkage equilibrium with each other (show your work)?
No: There are no AC combinations. Using the equation for LD:
LD = Freq (AC) x
Freq (ac) – Freq (Ac) x Freq (aC) = (0 x 0.25)  (0.50 x 0.25)= 0.125
c.
Are
B
and
C
loci in linkage equilibrium with each other (show your work)?
No:
There are no bC combinations. Using the equation for LD:
LD = Freq (BC) x
Freq (bc) – Freq (bC) x Freq (Bc) = (0.25 x 0.5)  (0 x 0.25) = 0.125
d.
Can you determine if these three loci are physically linked given the data?
Nothing definitive, although two are in LD, they may or may not be on the same
chromosome, however.
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 Spring '10
 Reinthal
 Ecology, Genetics, DNA, Sperm, Evolution, Mutation, mutation rate

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