Problem Set 4
BILD1 / Spring 2009
Genetics: Mendel’s Laws
Organisms with different genotypes can have the same phenotype! Is this statement true or false? Explain why.
TRUE. Dominant alleles carried in individuals with either homozygous or heterozygous genotypes could
result in identical phenotypes.
(a) In a diploid organism, how many different alleles at a single locus can that organism possess?
(b) How many different alleles of a particular gene can be found in a population of organisms?
(c) If there are 4 alleles that can occupy a single locus in a diploid organism, how many total different
genotypes are possible?
A a å
AA, Aa, Aå, A
, aa, aå, a
, åå, å
(d) Continuing with part (c), suppose that one of the four alleles is dominant over all the others. Further
suppose that the other three alleles produce identical phenotypes either when mixed with each other, or when
homozygous. Assign a phenotype to the genotypes you produced in part (c).
How many different phenotypes
TWO. Dominant phenotype (AA, Aa, Aå, A
) and recessive phenotype (aa, aå, a
, åå, å
The gene specifying blood group determinants can occur in three alleles: A, B and O. A and B are codominant,
while O is recessive. If Luke Skywalker’s mother was blood type A and Luke himself were type B, what blood type(s)
– if any – would DarthVader have to be to unequivocally rule him out
as Luke’s natural father?
Darth Vader could not
be his father if blood type A (AA or AO) or O (OO).
(Mom is AA or AO. Luke must be BO. Darth Vader can only be AB or BO.)
Cystic fibrosis is inherited as a simple autosomal recessive in humans. If a woman who is a carrier marries a
man who is normal and not carrying the trait, what percent of their children would be expected to have the disease?
Brown eye color is dominant in humans; blue is recessive. If a brown-eyed man marries a blue-eyed woman
and they have a brown-eyed boy and a blue-eyed girl, we can confidently conclude:
(a) the man is not the true father of one of the children