Table of Contents

• Prequiz...
• When linked genes stay linked...
• 1: Punnett Square Redux
• 2: Here's Smiley
• 3: Smiley's First Punnett Square
• 4: But what if the genes are linked?
• 5: Some notation
• 6: Since the linked genes don't separate...
• 7: Here's another one to try
• 7a: Here's another one to try
• ...And when they don't
• 8: But life is not so easy
• 9: Here's how the Punnett Square gets more complicated...
• 10: An easy Question
• 11: How about a general rule?
• The math of crossing over
• 12: But how often does cross-over occur?
• 13: Fun with map units...
• 14: The farther apart the genes are, the more they act like they're unlinked
• Getting an earful
• 15: Putting it all together
• 16: Spock's Ears
• 17: Yoda's Ears
• 18: Recomb - Review

A hybrid family

 

Mrs. Smiley	ET/et
Mr. Smiley	ET/et

Try the Punnett square for this hybrid family. Both Mom and Dad appear wild-type, but what will their kids look like?

If you're confused about what combinations are possible, remember that we're assuming (for the moment) that the chromosomes can't break apart. So what's on the left of the slash MUST stay together, and likewise what's on the right MUST stay together.

As we've been saying, each parent has two possible gamete types. They combine to make three genotypes, and 2 phenotypes.

The phenotypes are all wild-type vs. rabbit-toothed and bug-eyed, in a 3:1 ratio. (in other words, most of the kids appear wild-type and a few are double-variants).

If you think this sounds a lot like a single-locus cross, you're right... but don't start to think it's always that easy -- go to the next page instead...