Multiple Alleles, Incomplete Dominance, and
Codominance Problems
Some traits that we know about have more than two alleles for that trait. An individual can only have
two alleles for any particular gene location because chromosomes only come in pairs. However in
the population there may be more than two kinds of alleles that can occupy that gene location. Each
individual in the population will have some combination of two out of all of the possible alleles.
Inheritance of this type is called multiple allele inheritance. Assigning symbols for this type of
inheritance depends on several factors. See your teacher’s discussion of human blood groups for an
example.
1) In a newly discovered rodent (geomets), body fur is due to multiple alleles. There are three
alleles; brown (Fb); green (Fg); and albino (f). Both brown and green are dominant to albino,
but brown and green are codominant to each other. This genotype (FbFg) results in a fourth
phenotype - camo. List the possible phenotypes from the following crosses.
A) Camo x albino
B) Heterozygous brown x Heterozygous green
C) Heterozygous brown x Homozygous green
2) In a current civil suit, an owner of a female geomet that has a green body had a son who was
albino. She claims that a male with a camo body was the father, and wants financial support
from this individual’s owner. You are assigned as the judge in this case. Make your ruling with
an explanation supported by a Punnett Square.
3) In rabbits, normal fur coat color (F) is dominant to chinchilla (f c), which is dominant to
Himalayan (fh), which is dominant to albino (f). Phenotypically, what offspring may be
expected from the following crosses?
A)
Ffc x
fcfh
B)
fhf x
fhf
C)
fcf x fhf
4) What would the expected phenotypic ratio be in a cross between a man of blood type O and a
woman of blood type AB? Remember, type A and B blood types are codominant and type O is
recessive.
5) What would the expected phenotypic ratio be in a cross between a man who was
heterozygous A and a woman who was heterozygous B? Remember, type A and B blood
types are codominant and type O is recessive.
6) In a legal case, a woman of blood group AB claimed that a baby of Blood group O was her
baby. Knowing what you know about the inheritance of blood types, what would you say?
Remember, type A and B blood types are codominant and type O is recessive.