Mendelian Genetics—Dihybrid Crosses

Extra Resources

• The best place to learn this is at the DNA Learning Center.
• Be sure to do the problem.

Dihybrid Cross Setup

• Character: seed color
  • Traits
    • Yellow (dominant)
    • Green (recessive)
• Character: seed coat
  • Traits
    • Round (dominant)
    • Wrinkled (recessive)

The Results of the Cross

Figure 14.7(b), page 245, Campbell's Biology, 5th Edition

The Explanation

• P generation:

  Yellow, round (pure)	×	Green, wrinkled (pure)
  YYRR	×	yyrr

• F₁ generation:
  • All YyRr
  • Now there are four possible gametes from each parent: YR, Yr, yR, yr
  • This happens because of Mendel's Second Law: traits independently assort.
• F₂ generation:
  • Results from crossing two hybrid individuals (YyRr): thus it is called a dihybrid cross.
  • Requires a big Punnett square (16 cells).
  • Results in a phenotype ratio of 9:3:3:1.