KEY: Chromosomes and Genes - A Simulation

Original Document: Chromosomes and Genes

Objective: In this simulation you will examine how alleles are inherited in an organism.....

This activity assumes that students are familiar with mendelian genetics and understand that alleles are carried on chromosomes. The hands-on aspect helps students visualize the process of creating games (segregation and independent assortment) and combining chromosomes in the offspring (recombination). It goes a step further to show how alleles that are located on the same chromosome do not follow the typical Mendelian patterns.

Construct Your Parents

In your bag you have 6 chromosomes, represented by pipe cleaners. The white represent autosomes, and the red and blue represent sex chromosomes. Blue for Y, Red for X

You also have beads to represent the alleles for the following traits. You only have 4 white chromosomes for the three traits: blood type, tails, and ears because the tails and ears alleles are located on the same chromosome.

Check to make sure the bags have the correct chromosomes, if you have multiple classes, your students might have not put them back into their bags appropriately. Chromosomes are constructed with pipecleaners, also called chenille stems and can be purchased at most craft stores. You will need white to represent the autosomes and blue and pink to represent the sex chromosomes. I also cut them to make it easier to pair up homologs by size.

The beads can be different colors as long as your students know which color represents which trait.

Parent Genotypes

Male

** The dominant alleles TR are on different chromosomes

Check to make sure that there is no bead on the Y (blue) chromosome

Female

** The dominant alleles TR are on the same chromosome

Using the pipe cleaners and beads, one partner constructs the male genotype, and the other constructs the female genotype.

Have your teacher check your chromosomes before proceeding! If you got this step wrong, your simulation data will be wrong.

Make Your Predictions

With the parents genotypes given. Predict the phenotypic ratios for each trait, using a punnet square method. Show your work and calculations below

Coat Color XBY x XBXb Expect to have 1/2 of the females spotted 1/2 females black 1/2 males black 1/2 males white

Blood Type   Expected 1/4 AB; 1/4 A; 1/2 B

Tails & Ears Male TtRr (dominant on separate chromosomes) Female TtRr (dominant on same chromosomes) 1/2 normal tails, round ears 1/4 normal tails, pointed ears 1/4 bobtails, round ears

Run the Simulation

As parents, you will contribute HALF of your genes to the offspring. For each chromosome set, place behind your back and have your partner choose at random which chromosome will be donated to the offspring. One chromosome of each type must be donated from each parent, so that the offspring has a complete set. The offspring will probably not be like either of the parents.

You will repeat this process 12 times to complete the data table below. For each offspring, list the phenotype for each trait.

	Sex	Coat Color	Blood Type	Tail	Ears
Offspring 1
Offspring 2		Answers will vary depending on random chance. See ratios expected above. There should never be any spotted males!
Offspring 3
Offspring 4
Offspring 5
Offspring 6
Offspring 7
Offspring 8
Offspring 9
Offspring 10
Offspring 11
Offspring 12

Analysis

1. Compare your predicted values with your actual values (from the simulation).

	Black Females	Spotted Females	Black Males	White Males	Type AB Blood	Type A Blood	Type B Blood	Normal tail, round ears	Normal Tail, pointed ears	Bobtail, round ears	Bobtail, pointed ears
Actual (from simulation)				Answers Vary
Predicted (from Punnett)

2. What would you expect the phenotypic ratios to be if the alleles for tail length and ear shape were NOT located on the same chromosome? You would get a 9:3:3:1 ratio

3. What chromosomal anomoly would allow for a male to be spotted?
the male would need to have an extra X chromosome, XXY