MONOHYBRID CROSS WORKSHEET # 2
Answer on your own notebook paper
Problems 1-2 involve incomplete dominance.
1. In tomato plants, flat leaves (F) are dominant to tightly curled (f). In heterozygous plants, leaves are slightly
curled. What are the F1 genotype and phenotype ratios for the cross of a homozygous dominant with a
homozygous recessive?
2. Take two offspring from the F1 generation from problem 1, cross them to get an F2 generation, and give
genotype and phenotype data.
Problems 3-5 involve codominance.
In some types of cattle, when a red bull (RR) is mated with a white cow (WW), the offspring are a mixture of
red and white called roan (RW) . For the following crosses, give the genotypes of the offspring and the ratios in
which you would expect them to occur.
3. Cross a red bull with a roan cow.
4. Cross a white bull with a roan cow.
5. Yellow coat color in guinea pigs is produced by the genotype YY, cream color is due to the genotype YW
and white color due the genotype WW. If two cream colored animals are crossed, give the genotypic and
phenotypic ratios of the offspring.
Problems 6-9 involve dominant/recessive, polygenic and/or multiple allele traits
Note the following color relationships in horses:
BAY BB or Bb or Br
White
bb
RED RR or Rr or Rb
Gray
rr
Dapple
BUCKSKIN BR
br
6. A red male horse is bred to a dapple female, and the offspring is gray.
a.
What are the genotypes of the parents?
b.
What is the probability of offspring being gray?
c.
What is the probability of offspring being red?
d.
You have a herd of horses with bay, red, white and gray males. A red mare has given birth to a
buckskin filly. What color is the sire?
7. A heterozygous Bay horse(Bb) is mated with a heterozygous Red(Rr) horse. What are the genotype and
phenotype offspring probabilities?
8. 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 (This indicates incomplete dominance).
How many teeth would a AaBbCc Snarlymonster have?
9. List the phenotypic ratios (how many teeth) of all the potential offspring for the cross AABBCc x AAbbcc .