Dihybrid & Test Crosses

  • The natural progression for Mendel was to study 2 characteristics at the same time.
  • The study of 2 pairs of contrasting traits at the same time.
  • Ex. Round yellow seeds x wrinkled green seeds

The Law of Independent Assortment

  • During gamete formation, segregating pairs of unit factors assort independently of each other.
  • i.e. Colour is inherited independently of seed shape.

What are trait characteristics?

  • Round is dominant over wrinkled
  • Yellow is dominant over green

   This is the first generation of pea plants.

Now let’s find the phenotypes of the second generation.

 This is the second generation of pea plants

Test Crosses

  • Used to tell what genes an organism has.
  • Tall is dominant over short
  • TT = Homozygous
  • Tt = Heterozygous

You have a plant that is tall.

Is it homozygous or heterozygous?

  • To know this, Mendel did a test cross!

To do a test cross, mate the genotype with a homozygous recessive individual.