Exam 3 Sample Short Answer Questions.
1. A heterozygous plant (AaBb) is backcrossed with its homozygous recessive parent. Assuming
independent assortment, what would the genotypes and phenotypic ratios be?
The actual results of the cross are:
Dom-dom - 170
Dom-rec - 15
Rec- dom - 15
Rec-rec – 170
Explain the results and calculate the distance between the genes.
2. Red-green blindness is an X-linked recessive mutation. What are the probabilities for a child to have
the color blindness if the father is color-blind and the mother has normal color vision, but her father is
color-blind? Show the Punnet square.
3. A normal pigmented man marries an albino woman. They have three children, one of which is
albino. What is the genotype of the father? Show the Punnet square.
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4. Why and how do DNA strands replicate in the opposite direction?
5. In peas tall height is dominant to short height and yellow pod color is dominant to green pod color.
The genes are not linked. A homozygous tall-yellow pod plant is crossed with a homozygous shortgreen pod plant. Give the genotypes and phenotypes of a backcross between a F1 plant and the
homozygous recessive parent. Show a Punnet square.
6. Compare meiosis and mitosis. Include how prophase in mitosis is different from prophase I in
meiosis?
7. A man has six fingers on each hand and six toes on each foot. His wife and their daughter have the
normal number of digits. Remember that extra digits is a dominant trait. What is the probability that a
son or daughter will have extra digits? Show the Punnet square.
8. A black guinea pig crossed with an albino guinea pig produces 12 black offspring. When the albino is
crossed with another black one, 7 black and 5 albinos are obtained. What is the explanation for this
genetic outcome? Write genotypes for the parents, gametes and offspring.
9. Describe one of the experiments that led to the conclusion that DNA is the genetic information in a
cell. Be specific.
10. Draw a short piece of DNA to include 3 base pairs. Show the nucleotide structures. You may use
letters for the bases but not the other nucleotide components.
11. Describe the cell cycle. How is the cycle controlled? What happens in the conversion of a cell from
the normal condition to a cancerous condition?