Ask A Scientist© Molecular Biology Archive

name         Milton
status       educator
age          40s

Question -   I am teaching middle school genetics to my group of
honors science students.
We are working on Punnett Squares completing trihybrid crosses and what
I am calling quadhybrid crosses (16 x 16).  My question is this--
What do you call a cross with 4 characteristics?  I can find no place
on the internet that shows sample problems called "quadhybrid".

I would call them tetrahybrids.
I also teach Genetics (but college level) and I've found that combining
multiple characteristics into a single Punnett square is unnecessarily
complicated (and confuses many of my students).  You can keep each
characteristic in a simple 2 x 2 Punnett square and just multiply
probabilities to determine the number in each class.  For example, for a pair
of characteristics that gives you these tables:

    A  a             B  b
A AA Aa          B  BB Bb
a Aa aa     and  B  BB Bb

The chances of
AA are 1/4
Aa are 1/2
aa are 1/4
BB are 1/2
Bb are 1/2

so to get AABB, it's 1/4 * 1/2 = 1/8
for AaBB, its 1/2 * 1/2 = 1/4.

This also saves you the trouble of working out an enormous table that is easy
to mess up in front of the class.

Christine Ticknor
Ph.D. candidate
Yale University
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It is a multihybrid cross.  It is most easily computed using the algebraic
system for determining the outcomes rather than the typical punnett square
method.

pf
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I don't think most classes go this far-thus no mention of the process
anywhere.  But if three traits are called trihybrid, I think tetrahybrid
would be the next logical step.
van hoeck
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