DIHYBRID CROSS EXAMPLE
Now You Try!
In humans, the gene that causes a unibrow (u) is
recessive to not connected eyebrows (U); the
gene for thick lips (T) is dominant over the
gene for thin lips (t). If a male that is
homozygous for not connected eyebrows and
heterozygous for thick lips mates with a
woman who has a unibrow and is
heterozygous for thick lips, what is the
phenotypic ratio of the offspring?
How do you set it up?
• Genotypes
U = not connected eyebrows
--Dad = UUTt
u = unibrow
--Mom = uuTt
T = thick lips
t = thin lips
• Possible Different Combinations of Alleles
--Dad = UT or Ut --Mom = uT or ut
dad
2. Make one row for
each possible
different combination
of alleles from mom
UT
m
o
m
Ut
1. Make one
column for each
possible different
combination of
alleles from dad
uT
3. Fill in the boxes
ut
Results of the Cross
UT
uT
Only include the
phenotypes
present in the
results.
ut
UuTT
UuTt
Ut
UuTt
Uutt
Phenotypic Ratio
3 not connected eyebrows & thick lips : 1 not connected eyebrows & thin lips