Friday, 12 April 2013

Sandwich Mating (Activity to increase understanding of dihybrid crosses)


There is a little known creature that exists in Sandwichland.  It only comes out on cold winter afternoons, or when there’s large bowls of tomato soup around.  Some of these creatures have a best friend named ketchup, while others are more solitary.  They come in many different shapes and sizes. But they are not all about their fancy breads and toppings.  They don’t want to be noticed in a superficial way like all these Paninis nowadays, no, they hearken back to gentler time, a cheesier time.  This is the story of a few glorious members of the grilled cheese people, and their quest for a mate and the brilliance of the children produced.

Each grilled cheese sandwich has two genes – cheese and bread
Alleles are versions of how a gene will be expressed.  In Sandwichland, there are not so many varieties.  In fact, there are only two alleles for each gene.  But that’s o.k. (if you’re not o.k. with that, just back up off me)
1.       Bread Alleles – White or Brown – White is dominant (not for health reasons, but for taste reasons)
2.       Cheese Alleles – Cheddar or Kraft Singles (pretty sure it’s cheese, but not positive) – Kraft Singles – dominant
** Each sandwich, of course, has two slices of bread and two slices of cheese (no one ever puts one on there) **

A - Complete the following crosses.

For each cross there may be more than one possibility for the genotype of the offspring.  You must make the sandwich for each possible genotype. You also must show the crosses in full, on a separate page. (P1, F1, and phenotypic ratios)
1.       homozygous white, homozygous Kraft   X  homozygous brown, homozygous cheddar
2.       heterozygous bread, homozygous Kraft  X  homozygous brown, homozygous cheddar
3.       heterozygous bread, heterozygous cheese  X  homozygous white, homozygous Kraft
4.       heterozygous bread, heterozygous cheese  X heterozygous bread, heterozygous cheese

B Storytime, with a question

Within the annals of history of the Sandwichpeople, there is record of a tale filled with deceit and intrigue.  It fell in into legend but resurfaced recently on a popular daytime talk show.  The story goes as follows:  Icabod Von Holstein, one of the most influential and rich Sandwichpeople was married to a beautiful sandwich named Charlize Theron.  Icabod was away on business, trying to merge the cheddar company with Velveeta, and upon his return Charlize informed him she was with child.  Now, they had been intimate before his departure,  but Icabod had doubts.  Icabod had always had a nagging suspicion about Charlize’s intentions, she was his 7th wife after all.  2 months later(That’s the gestation. In sandwich time. In the story.)Charlize brought forth into the world, a white sandwich that had cheddar within.  Now, Icabod was from a long line of white breaded sandwich folk, but cheddar was not flowing through their veins.   However, Icabod’s family had a muddled past with rumors of an extra-sandwical affair where his great grandmother gretta von Holstein had taken to a stable boy from meager cheddar lineage.  Could Icabod have fathered the child? Charlize was homozygous white, heterozygous cheese.  Illustrate using punnet squares how Icabod could have been the father or not.  Choose one outcome from the squares and complete the story.  (one paragraph)

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