Test Crosses
1. In Labrador dogs, black fur is dominant over chocolate fur. A breeder of a pure bred, black
Labrador is looking for a mate for their dog to breed with. The breeder answers an
advertisement in the newspaper that says there is an individual who owns a black Labrador and
is looking to breed their pet as well. Even so, the individual from the newspaper does not have
papers on their dog to prove that it is pure bred.
a) EXPLAIN (write out in words) how a test cross could show if the dog is pure bred for the
dominant black color.
b) If the dog proved not to be pure bred for the black color, show the punnett square that
would demonstrate this situation. Circle the offspring that would be black.
c) Show the punnett square that would demonstrate that the dog IS pure bred for the black
color. Circle the offspring that would be black.
General Genetic and Mendel Review Questions
2. What was the blending hypothesis that many people believed to be true concerning genetics
before Mendel (from yesterday’s Bozeman video)?
3. What were P, F1, and F2 generations for Mendel (Don’t just say Parent, First Generation, Second
Generation)?
4.
5.
6.
7.
What is the law of segregation?
What phase of meiosis does the law of segregation occur in?
What is the law of independent assortment?
What phase of meiosis does the law of independent assortment occur in?
8. Why do dominant alleles “dominate” or “mask” recessive alleles in heterozygous individuals?
9. Explain the difference in the following terms:
a. allele, a gene, and homologous chromosomes.
b. homozygous and heterozygous.
c. genotype and phenotype
10. Perform a cross between a homozygous tall pea plant with a short plant (tall is dominant). Give
the genotype and phenotype ratios.
11. Perform a cross between a heterozygous tall pea plant with terminal flowers with a homozygous
tall pea plant with heterozygous axial flowers (tall is dominant; axial flowers are dominant).
a. Give the phenotype ratio.
b. What portion of the offspring would be Ttaa?
c. What portion of the offspring would be tall with axial flowers.