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Punnet squares Monohybrid, Dihybrid, and Trihybrid Crosses

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Dihybrid cross

Let’s say we cross breed two organisms – plants or animals – and they follow simple inheritance rules.

* The parents differ in two characteristics (height and eye color!  Or eye color and number of fingers!  Or hair color and freckling. Any two possible combos.)

* Each characteristic is determined by a single gene.

* Each gene has two alleles (meaning – the gene comes either in one form or another. Only two choices)

If all this is true, then we can figure out the odds of what their offspring will be by using a 2×2 Punnett square. We call this a dihybrid cross.

Dihybrid cross

from science.oregonstate.edu, genbio

 

Here is a simplified Punnett square diagram for eye color.
(This assumes that only 2 genes control eye color; of course, in reality more genes are involved!)

Trihybrid cross

Let’s say we cross breed two organisms – plants or animals – and they follow simple inheritance rules.

* The parents differ in three characteristics (e.g. height, eye color and number of fingers!)

* Each characteristic is determined by a single gene.

* Each gene has two alleles (meaning – the gene comes either in one form or another. Only two choices)

If all this is true, then we can figure out the odds of what their offspring will be by using a 3×3 Punnett square. We call this a trihybrid cross.

trihybrid cross

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