Molecular Genetics BSCI410
Homework 4; Lectures 1318  answers
Homework due at the
beginning
of class on
Thursday, Nov. 11, 2010.
The exam will be Nov. 18.
Homework and review questions will be discussed again at the review on Nov. 16.


1
Homework questions
. Please provide your answers on a separate sheet.
Examine the following pedigree.
A
1,2
B
1,2
A
1,3
B
1,3
A
1,2
B
1,2
A
1,2
B
1,3
1. (1 point) The A
1
alleles in the two brothers are identical by state (this just means that they are
both A
1
). Can you infer that they are also identical by descent?
B)
You can conclude that A
1
is identical by descent.
Notice that A2 had to come from the father (and therefore, A1 is maternal in both cases).
2. (1 point) The B
1
alleles in the two brothers are identical by state (this just means that they are
both B
1
). Can you infer that they are also identical by descent?
C
) You can conclude B
1
is not identical by descent.
Notice, for the brother on left, that B2 had to come from the father (and therefore, B1 is
maternal). For the brother on the right, B3 is maternal so B1 is paternal. Thus, B1 is
maternal in one case and paternal in the other case.
(Questions 35) Consider two populations, 1 and 2, that differ at two
unlinked
loci, A and B. In
each population a specific allele is fixed at each locus (
i.e.
all individuals in population 1 are
homozygous for A
1
and B
1
 they have the genotype A
1,1
B
1,1
 while all individuals in
population 2 have the genotype A
2,2
B
2,2
).
You allow a large and equivalent number of individuals from the two populations  for example,
500 males and 500 females from population 1 and 500 males and 500 females from population 2 
to mate at random (and they do mate at random).
maternal A1, B1
maternal A2, B2
paternal A1, B1
A1/A1 B1/B1
A1/A2 B1/B2
paternal A2, B2
A1/A2 B1/B2
A2/A2 B2/B2
Thus
¼
will be A1/A1 B1/B1,
½
will be A1/A2 B1/B2 and
¼
will be A2/A2 B2/B2.
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Molecular Genetics BSCI410
Homework 4; Lectures 1318  answers
Homework due at the
beginning
of class on
Thursday, Nov. 11, 2010.
The exam will be Nov. 18.
Homework and review questions will be discussed again at the review on Nov. 16.


2
3. (1 point) Is locus A at HardyWeinberg equilibrium in the "G1" generation?
Yes
, from the forgoing, you can see that for A, the allele frequencies are p = q = 0.5 and the
genotype frequencies 0.25, 0.5 and 0.25 correspond to p
2
, 2pq and q
2
.
4. (1 point) What is the expected frequency of each of the four possible gametes transmitted from
the G1 to the G2. The possible genotypes are A
1
B
1
, A
1
B
2
, A
2
B
1
and A
2
B
2
3/8 A1 B1, 1/8 A1 B2, 1/8 A2 B1, 3/8 A2 B2
1/4 of the G1 will be A1/A1 B1/B1; they will generate only A1 B1 gametes (2/8)
1/4 of the G1 will be A2/A2 B2/B2; they will generate only A2 B2 gametes (2/8)
1/2 of the G1 will be A1/A2 B1/B2; they will generate equal numbers of the four possibilities (1/8 for each)
Summing those yields the answer above.
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 Summer '08
 SAXENA
 Genetics, Molecular Genetics, Genetic linkage, Chromosomal crossover, STSs

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