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Mix It Up
1. A homozygous (dominant) right-handed person marries a homozygous (recessive)
left- handed person. Determine the genotypes and phenotypes of their offspring.
Could two right-handed individuals have a child that is left-handed? Explain.
2. The organisms with the genotype LLGgMm will produce how many types of
gametes? Show how you came to this conclusion.
3. About 70% of Canadians get a bitter taste from the chemical phenyl
thiocarbamide (PTC), while the other 30% do not. The ability to taste this
chemical (T) is a dominant characteristic, while taste-blindness is recessive (t).
Tongue-rolling ability is dominant (R), while the inability to roll is recessive (r ) .
A tongue-rolling woman who is taste-blind for PTC has a father who could not
roll his tongue but could taste the PTC chemical. She marries a man who can taste
PTC but cannot roll his tongue. His mother was taste-blind to the chemical. Show
the possible children this couple could produce. Use a punnet square.
4. Explain what a test cross is, and give an example how you would use it.
5. In humans free earlobes are controlled by the dominant allele E, and attached by
the recessive allele e. The widow’s peak hairline is regulated by the dominant
allele H, while the straight hairline is controlled by the recessive allele h. What is
the probability that a child from the mating of EeHh X EeHh parents would be a
male with a widow’s peak and have attached earlobes? Show all of your work.
6. For shorthorn cattle, the mating of a red bull and a white cow produces a roan calf
that has intermingled red and white hair. Many matings of the roans produce the
following ratio: 1 red, 2 roan, 1 white. Explain the type of inheritance.
7. In a cross of purple-flowered and white-flowered plants, the F1 plants were all
lavender-flowered. A cross of two F1 plants resulted in 28 purple-flowered, 52
lavender-flowered and 19 white-flowered.
a) What were the F1 genotypes?
b) Use a Punnet square to show how the results observed in the F2 generation
were obtained.
8. Thalassemia is a serious human genetic disorder which causes sever anemia in the
homozygous condition (TmTm). People with thalassemia die before sexual
maturity. The heterozygous condition (TmTn ) causes a less serious form of
anemia. The genotype TnTn causes no symptoms of the disease. Indicate the
possible genotypes and phenotypes of the offspring if a male with the genotype
TmTn married and had children with a woman of the same genotype.
9. In humans, the recessive allele that causes a form of red-green colour-blindness
(c) is found on the X chromosome.
a) Identify the F1 generation from a colourblind father and a mother
homozygous for normal vision.
b) Identify the F1 generation from a father who has normal vision and a
mother who is heterozygous.
c) Draw a punnet square to show how parents could produce a colour blind
daughter.
10. A probationary nurse mixed up the identification bracelets of three newborn
babies. The blood types of the parents and babies were obtained in an attempt to
identify the parents of each baby.
Mr.Smith
Mrs.Smith
Mr. Rene
Mrs. Rene
Mr. Sharetsky
Mrs. Sharetsky
AB
O
O
O
A
B
Baby X
Baby Y
Baby Z
O
A
AB
Which baby belongs to which set of parents? Explain how you arrived at your
answer.
11. Haemophilia is caused by an X-linked recessive allele. A couple about to have a baby
is concerned that they may be carriers of the allele. Neither are haemophiliacs, but the
man's father and the woman's father are both haemophiliacs. What is the probability that
this couple could have a child with haemophilia? Use a punnett square.
12. Curly hair ( C) in humans is dominant to straight hair (c) on an autosome. Male
pattern baldness (Xb) is recessive to normal hair (XB) and is a sex-linked trait. Show a
punnett square of the cross between a homozygous curly-haired , female carrier of
baldness, and a homozygous straight-haired non-bald male. Use a punnett square and
give the genotypic and phenotypic ratios.