Beyond Mendelian Genetics.
1. In a certain cactus, prickly spines can be two pronged or one pronged. If a true breeding onepronged cactus is crossed with a true breeding two-pronged cactus, the F1 generation has a
mixture of spines, some are two-pronged, some are one-pronged.
a. Is this an example of codominance or incomplete dominance?
codominance, since both of the traits are expressed
b. Show the F2 generation (a cross between the two F1's). What are the phenotypes of the
offspring and in what proportion?
Ff x Ff ; 1/4 would be two-pronged, 1/4 would be one-pronged, 2/4 would
be mixed
2. In this same cactus, if you cross a plant that has red flowers to one that has yellow flowers,
you produce a plant that has orange flowers. Is this codominance or incomplete dominance?
Show the cross of an orange flowered plant to a red flowered plant.
This is incomplete dominance, since the hybrid shows neither trait. FF x Ff; 1/2
would be read, 1/2 would be orange
3. A red flowered, two-pronged cactus is crossed with a yellow flowered one-pronged cactus.
What are the resulting offspring and in what proportion?
RRFF x rrff = RfFf, all offpring are mixed prongs, and orange flowers
4. Show the cross of a cactus that is heterozygous for both traits crossed with one that has red
flowers and one-pronged spikes.
RrFf x RRff,
1/4 Red flowers, mixed prongs
1/4 Red flowers, one prong
1/4 Orange flowers, mixed prongs
1/4 Orange flowers, one prong
5. A man with type A blood is married to a woman with type O blood. What are ALL of the
possible blood types of their children?
Genetics: Multiple Allele Traits
Blood Type
Blood type is controlled by 3 alleles: A, B, O. A & B are codominant, O is recessive.
1. a) What are the two genotypes possible for a person who as A blood? ______________
b) What genotype does a person with AB blood have? _______________
c ) What genotype does a person with O blood have? _____________
d) What are the two genotypes possible for a person who as B blood? ______________
2. A man with type AB blood is married to a woman also with type AB blood. What percentage of their
children will have:
A blood? _______ B blood? ______ O blood _____ AB blood ________
3. A man has type B blood (genotype BB) is married to a woman with type O blood. What blood type
will all their children have? ________ What is the genotype of the children? ______
4. A woman with type A blood (genotype AO) is married to a type B person (genotype BO). What
proportion of their children will have:
A blood? _______ B blood? ______ O blood _____ AB blood ________
5. A woman with type A blood is claiming that a man with type AB blood is the father of her child who
is type B.
Could this man be the father of the child? _______________ Show the possible crosses; remember
that the woman can have AA or AO genotypes.
Assuming that he is the father, what must the mother's genotype be? _____
6. A man with type AB blood is married to a woman with type O blood. They have two natural children
and one adopted child. Jane has type A blood, Bobby has type B blood, and Grace has type O blood.
Which child was adopted? ____________________
A and O
6. A man with type AB blood is married to a woman with type O blood. What are all the possible blood
types of their children? A and B
7. Dwarfism in humans is a domininat trait that is also lethal if an individual inherits two copies. Show
the genotypes of a family wear both parents are dwarfs and they have 2 children, where one is a
dwarf and the other is not.
Dd x Dd (parents)Offspring are 2/3 Dd, 1/3 dd (normal)
8. Guinnea pigs can have curly or straight hair, where the curly gene is recessive. Guinnea pigs can
also have a condition called bowlegged, where their legs curve noticeably outward. Bowleggedness is
a dominant lethal allele if an individual inherits two copies of it (BB). Show the cross between a curly
haired, bowlegged guinnes pig and a heterozygous straight haired pig that is also bowlegged. How
many of their offspring would you expect to be normal with curly hair?
hhBb x HhBb
1/2 Hh (straight)
1/2 hh (curly)
2/3 Bb (bowlegged)
1/3 bb (normal)
Normal, curly = 1/3 * 1/2 = 1/6
9. In Snarlymonsters, the number of teeth is polygenic. The recessive condition (aabbcc) results in a
toothless Snarlymonster, and the dominant condition (AABBCC) results in a Snarlymonster with 6
teeth. There are 5 other possible variations.How many teeth would a AaBbCc Snarlymonster have?
The allele is additive, each capital letter indicates an add of a tooth, AaBbCc = 3
teeth
10. List the phenotypic ratios (how many teeth) of all the potential
offspring for the cross AABBCc x AAbbcc
AABbCc = 4 teeth
AABbcc = 3 teeth
11. Lethal white overo syndrome is an autosomal recessive gene which if
fatal 100% of the time and occurs in horses. Death of OLWS foals occurs
within a few days of birth. If heterozygous, the animal has a multicolored
patterned appearance, sometimes called a "paint". This pattern indicates
the horse is heteroyzogous. If two of these horses were bred, what
percentage of their offspring would be frame and what percentage would
die from OLWS?
1/4 will be normal coat color, no disorder
2/4 will be paints
1/4 will have OLWS
Multiple Allele Traits in Chickens
All chicken have combs on their heads, but it does not always look the same. The comb is a fleshy
growth on the top of the chicken's head. Both male and female chickens have combs, but the ones on
the male are larger. Combs of different breeds may look different in shape and even in color.
1. On the cross pictured, what must be the genotypes of the two parents for the outcome to always be
a walnut offspring?
____________ x _____________
2. Show a Punnett square for the following cross and describe the phenotypic ratios.
RrPp x RrPp
3. Show a punnett square for the following cross and describe the phenotypic ratios.
Single comb x Walnut (RrPp)
4. Show a punnett square for the following cross and describe the phenotypic ratios.
Single comb x Pea comb (rrPp)
5. A rose crossed with a pea produces six walnut and five rose offspring. What must be the
genotypes of the parents? Show the cross.