Modeling Monohybrid and Dihybrid Crosses

and the Law of Random Probability

Objectives:

· Predict the genotypic and phenotypic ratios of offspring resulting from the random paring of gametes.

· Calculate and graph the genotypic ratio and/or phenotypic ratio among the offspring of a monohybrid cross and dihybrid cross.

Part 1: Simulating Monohybrid Cross Possibilities:

You will model the "random" pairing of alleles by choosing shells from Petri dishes.

The shells will represent the alleles for having blue shell color (dominant "B" = blue shell) and having red shell color (recessive "b" = red shell).

Part 2: Simulating Dihybrid Cross Possibilities:

You will model the "random" pairing of alleles by choosing shells and beans from Petri dishes. The shells and beans will represent the alleles for having a blue shell color (dominant “B” = blue shell) and having a red shell color (recessive “b” = red shell); and being spotted (dominant "S" = spotted pinto beans) and not spotted (recessive "s" = white great northern beans).

While one partner records the results, the other partner needs to be blind folded or keep

his/her eyes closed at all times during the trial period. You may want to sit across from

each other to make the recording easier.

When the recording partner says go, start the clock for 10 minutes. The partner, with

their eyes hidden, needs to "simultaneously" pick up 1 allele from each dish and place

it on the lab table. As soon as the recorder can, return the alleles to the same dish in

order for the his/her partner to choose again when given the word. Remember, the more

you do, the better the results.