A Mendelian Review
The following questions will help you to test and extend your knowledge from this lesson. A Mendelian Review will remind you of some of the basic ideas from this lesson, while Problem Set 1 will challenge you to apply these ideas in new and more challenging ways.
A Mendelian Review
Assume that in pea plants, yellow pod color is dominant
over green pod color.
- Draw a Punnett square to illustrate the expected outcomes if a plant with two dominant alleles is crossed with a plant with two recessive alleles. (Need a little help getting started on drawing Punnett squares? Use this Web page by Ruth Rogers of FeatherSong Aviary)
- If we plant seeds from this cross and 400 plants grow, how many of the plants would we expect to be homozygous dominant? Hint! Homozygous recessive? Heterozygous? How many would we expect to have green pods? Yellow pods?
- Draw a Punnett square to illustrate the expected outcomes if two plants that are heterozygous for pod color are crossed together.
- If we plant seeds from this cross and 400 plants grow, how many of the plants would we expect to be homozygous dominant? Homozygous recessive? Heterozygous? How many would we expect to have green pods? Yellow pods?
Problem Set 1: An Introduction to Mendelian Genetics
In the distant past, an imaginary ship has washed up on an imaginary island in the not-so-imaginary Pacific Ocean. The imaginary crew includes an imaginary naturalist who has discovered a new species of imaginary reptiles that he, not so imaginatively, has named lizardos. The lizardos are tiny and ugly. They have two distinct colors: some are bright red, while others are bright yellow. Some lizardos have long tails, while others have stubby short tails. Our imaginary naturalist friend has managed to capture a small population of lizardos and has brought them on board the ship in order to learn more about their genetics. Answer the following questions.
- After performing a series of breeding experiments, the naturalist determines that yellow coloration in lizardos is dominant to red coloration. Draw a Punnett square to illustrate the expected outcomes if a red lizardo were mated with a lizardo that was heterozygous for coloration. If the clutch produced includes 16 eggs, how many yellow lizardos would you expect? Hint!
- A yellow female lizardo and a red male lizardo have become particularly close. However, over many matings that have produced over 15 living offspring, the pair has never produced a red lizardo. What is the male lizardo's genotype? What is the female lizardo's most likely genotype? Hint! Can you be 100% sure about the female's genotype? Why or why not?
- Two red lizardos mate. If they have four offspring of their own, how many of these offspring would you expect to be red?
- Assume that tail length in lizardos operates on a system of complete dominance like Mendel described. Design a breeding experiment that the naturalist could undertake in order to determine which allele, long or short, is recessive. What are the possible outcomes of this breeding experiment? What would each outcome reveal to you? While designing your experiment, you may also assume that the naturalist has spent enough time with his reptilian buddies to determine which individuals are true-breeding and which are not.
- After following your instructions, the naturalist performs the experiment and finds that short tail length is dominant over long tail length in lizardos. The naturalist now mates a yellow female with a short tail with a yellow male with a short tail. He knows from previous experiments that both lizardos are heterozygous for both traits. Draw a Punnett square to illustrate this dihybrid cross (for a model of what this might look like, refer to Figure 10-7 on page 200 of Reading Assignment 8).
- If the lizardo couple in Question 5 had 16 offspring, how many of them would you expect to be red? How many would you expect to be yellow? How many would you expect to be orange? How many would you expect to have long tails? How many would you expect to have short tails? How many would you expect to be red with short tails? How many would you expect to be red with long tails? How many would you expect to be yellow with short tails? How many would you expect to be yellow with long tails?
