DI-HYBRID CROSSES

Unit 4 Part 2

Di-Hybrid Crosses

Genetics Problems don’t always involve only one trait.

When they involve 2 traits (Ex. Corn kernel shape and corn kernel color) we call it a di-hybrid cross.

How to Solve method #1

In Guinea pigs BLACK fur is dominant to WHITE fur and SHORT hair is dominant to LONG hair.

Black (F) White (f) / Short (H) long (h)

Method #1 – Guinea Pigs

Example Problem:

A heterozygous black, long haired guinea pig

mates with a white, homozygous short haired

guinea pig.

How to Solve method #1

You must first write down your parental genotypes: Heterozygous black = Bb Long haired = hh White = bb Homozygous short = HH

Next find the possible gamete possibilities (what will go on the outside of the punnett square) FOIL method

First – Outer – Inner - Last

Bbhh bbHH

How to Solve method #1

Gamete possibilities:

Bh, Bh, bh, bh

Gamete possibilities:

bH, bH, bH, bH

Bbhh x bbHH

How to Solve method #1

Next, fill in the gamete possibilities around your LARGE punnett square. You need 16 boxes!

How to Solve method #1

Bh Bh bh bh

bH

bH

bH

bH

How to Solve method #1

Lastly, complete the genotypic and phenotypic ratios (Phenotypic is the MOST important)

GR: ______BBHH ______BBHh ______ BBbb ______BbHH ______BbHh ______ Bbhh ______bbHH ______bbHh ______ bbhh

PR: _____Black/Short _____Black/Long_____White/Short _____White/Long