Solving a Genetics Mystery:
The Case of Farmer Funks Funky Dihybrid Corn
It was a dark and stormy night
or not. In fact, it is a hot and humid late-summer day on a farm in western Pennsylvania. The beans are ready for picking, the tomatoes are heavy on the vine and the cucumbers look like baseball bats. You pull into the gravel, daisy-lined driveway and your mouth is watering already at the sight of all this delicious produce. But you remember that you arent here to tank up on vegetables when you see a distressed Farmer Mack Funk heading toward you across the strawberry patch. Thats right youre here on a mission a genetics mystery case that Farmer Funk is calling on your special expertise to help solve.
The problem lies in the corn. It only takes a couple of minutes to notice what is missing from Farmer Funks roadside stand that delicious-when-roasted-and-salted-and-dripping-in-butter corn. So what is the deal with the corn? Well, here are the facts:
- Farmer Funk usually grows four purebred types of corn, each sold to different markets. Most of the corn is sold, but some of it is saved to be used for seed the next year:
- Yellow starchy: plump, yellow kernels that are tasty eaten off the cob (sold at the roadside stand).
- Yellow sweet: wrinkled, yellow kernels that make excellent animal feed when dried and ground.
- Purple starchy: plump, purple kernels that are sold to Purple Corn Chip manufactures.
- Purple sweet: wrinkled, purple kernels that are dried, ground and used for making purple food dye.
- The alleles controling for the (1) color and (2) starchiness of the corn (the two traits Farmer Funk is concerned with in his corn) are as follows:
- R (Purple) = dominant
- R (Yellow) = recessive
- Su (Starchy) = dominant
- su (Sweet) = recessive
- Farmer Funks corn fields are arranged in the following manner:
- Each kernel of corn on a cob is a seed, a diploid embryo that will grow into a new individual with the same genotype as the seed itself.
- Corn plants usually self-pollinate (one plant fertilizes its ovules/eggs with its own pollen/sperm to produce seeds). As a result, the kernels or seeds from purebred parent plants grow into purebred offspring plants and so on, since all the pollen and ovules carry the same alleles. However, corn can cross-pollinate between two different plants, which is exactly what happened to poor Farmer Funk
- The Problem:
In all his twenty years of farming, Farmer Funk has only grown purebred corn (homozygous for the color and starchiness genes). However, in the past two years, his crop has begun to produce some "funky" corn that has a mix of different types of kernels on one cob. This funky corn is no good to Farmer Funk because he cant sell it in any one of his four markets and he has to throw it out. What he needs from you is to find out:
- What went wrong?
- How can Farmer Funk return to producing crops of purebred corn?
Part I:What went wrong?
In order to help Farmer Funk solve this mystery, you have brought in your team of Genetics Sluths, fully equipped with strong genetics backgrounds, Punnett Squares and understandings of probability. Farmer Funk has provided you with four different samples of the funky, mystery corn, in order that you can figure out:
- What are the phenotypes/genotypes of the kernels/seeds on the funky corn cob sample you are examining?
- What were the genotypes of the parent plants that produced each sample of funky corn?
- In what generation did the original cross-pollination between the purebred types occur? What were the genotypes of these purebred types?
Your task: In order use your time and efforts most efficiently, you will break into four task teams and each team will answer the above questions for one of the corn samples. You will then re-group and explain your findings to the whole team.
*** In order to make your explanation as clear as possible, draw a visual map of what happened, showing:
- Each of the generations
- The crosses that occurred
- Punnett Squares representing these crosses, showing the offspring genotypes and the ratios in which these genotypes occurred.
Part II: How to return to the purebred lines?
Now that you know the genotypes of the seeds on your sample of corn, you need to help Farmer Funk figure out how he can best return his crop to its purebred status. Here is what you need to know:
- Farmer Funk had to sell all of his purebred corn this season since so much of his crop was funky. As a result, he now only has the funky corn to use as seed for next planting season.
- You should assume that the plants grown from this seed will self-pollinate and that you will be able to help Farmer Funk arrange his fields in a way that will prevent future cross-pollination between plants.
- Farmer Funk leads a busy life (10 children, captain of his bowling team, state-champion amateur long distance runner, biology substitute teacher etc.) and it would be entirely impossible for him to find the time to individually sort through seeds on a cob of corn for planting. You should assume that he can sort through cobs of corn to decide whether or not to plant them, but not the individual seeds.
- Farmer Funk does not want to have to be picking through cobs of corn and deciding whether or not to plant them for the rest of his life. He wants his crop to be entirely purebred in no more than five years. Your job is to help him do this as quickly and cost-effectively as possible.
Here is the information you need to provide for Farmer Funk:
- How many generations of self-pollination will it take to create purebred seeds and plants?
- What will the genotypes of these purebreds be?
- What is the method that Farmer Funk should use for selecting only purebred individuals? Practically, how is he going to complete this task?
- How should Farmer Funk arrange his fields differently to avoid further cross-pollination?
Your Task: Again, break into your four task teams to solve this problem. Each team will be responsible for only type of the funky corn.
***Draw a visual plan of what will happen when Mack Funk plants the seeds from your cob of funky corn, showing:
- Each of the generations
- Punnett Squares showing the possible genotypes of the seeds and the ratios in which they will occur from the self-pollinations.
- Which cobs Farmer Funk should select to plant and which he should throw away.
Now that you have figured out (1) what went wrong and (2) how to return Farmer Funks crops to their purebred status, you need to put this information together into a report. The report is for Farmer Funk so that he can actually carry out your plan. It is also to be kept as a record of the whole ordeal to refer to later should you be called on to solve a similar problem. Your report should include the following:
Title (5 points): What were the problems and how did you solve them?
Problem (5 points): IN YOUR OWN WORDS, state what the problems were.
Background Summary (20 points): Make sure you give enough information here that someone who was unfamiliar with the case (but very familiar with genetics!) could read this section and know what was going on.
- What was the general scenario? (4)
- What types of corn did Farmer Funk normally have? (4)
- What is the new funky corn? Where did it come from? (4)
- Why does Farmer Funk want to get rid of this funky corn? (4)
Your Method (10 points): Explain your approach to solving the two main problems.
- What did you do?
- How and why did you do it?
Initial Results: Part I (30 points): You are only expected to report on the funky corn cob sample that you worked with for Parts I and II.
- Your map showing the where the original cross-pollination occurred, the genotypes and ratios in which they occured in the following generations and the genotypes of the seeds on your funky cob. (15)
- A written explanation of your map. This should be like a story of what went wrong and what happened after that. (15)
Proposed Plan: Part II (30 points):
- Your visual plan of what Farmer Funk should do return his crops to their purebred status. Make sure that this is complete and easy to understand (15).
- A written explanation of what Farmer Funk should do (10). Be sure to also include:
- Justification for which cobs he should choose to plant (this should be based on genetics and economics!) (3).
- A drawn plan of how Farmer Funk should change the arrangement of his fields to avoid further cross-pollination between purebred types (2).
- Even though this was a group effort, you are responsible for writing your own, individual lab report. Consult with your team members, but be sure that what you turn in is your own, unique work, written in your own words.
- In addition to whether or not you include basic information, you will be graded on:
- the clarity and detail with which your present your ideas.
- the neatness and thoroughness of your work.
- the demonstration of your knowledge of genetics.
- DUE NEXT LAB DAY