13 Jun MBG*2040 – Recall that Mendel examined a gene that controlled the texture
Question
MBG*2040 Genetics Assignment #3
Name: _________________________________________ ID#_____________
Tutorial Day and Time:____________________________________________
TA name:
1. Recall that Mendel examined a gene that controlled the texture of the pea
seed (alleles W and w) and a gene that controlled the colour of the seed (alleles
G and g). Mendel determined that these genes were independently assorting.
a) Imagine that gene G is on chromosome 1 and gene W is on chromosome 3,
what phenotypic ratio (show all phenotypes) would be expected when a dihybrid
is test-crossed? Show your work.
b) Imagine that genes G and W are 30 map units apart on chromosome 3, what
phenotypic ratio (show all phenotypes) would be expected when a dihybrid is
test-crossed? Assume the alleles are in cis configuration in the dihybrid. Show
your work.
c) Imagine that genes G and W are tightly linked on chromosome 3, what
phenotypic ratio (show all phenotypes) would be expected when a dihybrid is
test-crossed? Assume the alleles are in trans configuration in the dihybrid. Show
your work.
MBG*2040 Fall 2012 Assignment #3 Page 1 of 6
Name: _________________________________________ ID#_____________
d) Imagine that genes G and W are 80 map units apart on chromosome 3, what
phenotypic ratio (show all phenotypes) would be expected when a dihybrid is
test-crossed? Show your work.
2. In rabbits, solid-coloured coats (S) is dominant to white-spotted coats (s) and
short hair (L) is dominant to long hair (l). Imagine that gene S is linked to gene L
and they are 12.5 map units apart. True-breeding solid-coloured, short-haired
rabbits are crossed to true-breeding white-spotted, long-haired rabbits.
a) What is the genotype of the F1 rabbits? The genotypes must show linkage.
b) The F1 offspring are test-crossed. What percentage of the test-cross progeny
will have white spots and short hair? Show your calculations.
c) The F1 offspring are intercrossed. What percentage of offspring will be
dihybrids? Show your calculations
MBG*2040 Fall 2012 Assignment #3 Page 2 of 6
Name: _________________________________________ ID#_____________
3. Imagine the genes for red-green colourblindess and haemophilia are 30 map
units apart on the X chromosome. Examine the pedigree below. The letters
below the symbols tell you if the individuals is affected with haemophilia (h) or
colourblindness (cb) or both (cb+h).
normal
cb
cb
cb+h
h
normal
h
normal
normal
cb
a) Number the generations and individuals in this pedigree.
b) Write genotypes (and their probabilities) for all individuals in the pedigree.
Make sure your genotypes are written to show linkage.
c) List the gametes and their proportions that can be produced by II-2.
MBG*2040 Fall 2012 Assignment #3 Page 3 of 6
Name: _________________________________________ ID#_____________
d) What is the probability that the next child of II-2 will be a son with
colourblindness and normal blood clotting? Show your work.
e) List the gametes and their proportions that can be produced by III-4.
f) Question will be given in tutorial.
g) Question will be given in tutorial
MBG*2040 Fall 2012 Assignment #3 Page 4 of 6
Name: _________________________________________ ID#_____________
4. Nail-Patella Syndrome is caused by a rare dominant allele, N. This locus is 20
map units from the ABO blood type locus. The pedigree below shows the
inheritance of these two traits. Shaded individuals are affected with Nail-Patella
Syndrome.
A
O
AB
A
B
AB
a) Number the generations and individuals in this pedigree.
b) Write genotypes (and their probabilities) for all individuals in the pedigree.
Make sure your genotypes are written to show linkage.
c) List the gametes and their proportions that can be produced by II-1 and II-2.
MBG*2040 Fall 2012 Assignment #3 Page 5 of 6
Name: _________________________________________ ID#_____________
d) What is the probability that the first child of II-1 and II-2 will have Type AB
blood and Nail-Patella Syndrome? Show your work.
e) What is the probability that the first child of II-1 and II-2 will have Type O blood
and be phenotypically normal? Show your work.
f) The first child of II-1 and II-2 is born and the baby has Type B blood. What is
the probability that this baby also has Nail-Patella Syndrome? Show your work.
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