INTRODUCTION TO GENETICS PROBLEM SOLVING
NAME _________________________________ DATE ______________________
These are the terms you will have to become familiar with to solve genetics problems:
Gene
Hybrid
F2
Genotype ratio
Self fertilization
genotype
purebred
punnett square
homozygous
cross fertilization
phenotype
parental cross
phenotype ratio
heterozygous
monohybrid cross
allele
F1
dominant
recessive
testcross
1. How do the terms gene and allele differ from each other?
2. In peas, tall stems are dominant to short stems.
a. What are the genotypes of each of the following:
- homozygous tall ____________________________
- short ______________________________________
- pure tall ___________________________________
- hybrid ____________________________________
- heterozygous tall ____________________________
b. If a plant breeder crosses a homozygous tall and a short plant, what genotypes
are possible and in what ratio?
c. If the breeder then bred two of the offspring plants, what genotypes are
possible and in what ratio?
3. Do a punnett square and predict the offspring of a cross between a heterozygous
yellow pea and a homozygous green pea plant. Give the expected genotype and
phenotype ratios.
4. Cross a homozygous tall plant with a heterozygous tall plant. What % of the
offspring would be expected to be short?
5. If you cross two hybrid purple plants and then crossed any white offspring what color
would you expect in the F2 generation?
Now try these multiple choice questions:
6. When hybrids are crossed, the genotype ratio of the offspring is
A.) 1:1 B.) 3:1 C.) 1:2:1
D.) 4:1 E.) 3:2
7. If a pair of hybrid black guinea pigs are mated, and there are four offspring, their
appearance may be
A.) all black B.) 3 black: 1 white C.) 2 black: 2 white D.) 1 black: 2 white
8. For a guinea pig, black coat (B) is dominant to white coat (b). If two of them mated
and produce 75% offspring with black coats and 25% offspring with white coats, the
genotypes of the parents are most likely
A.) BB x BB B.) Bb x BB C.) BB x bb D.) Bb x Bb E.) bb x Bb
9. Give an example of a situation that would require a testcross. Be as specific as
possible. How would the results of the test cross provide you with the information that
is sought?