Mississippi Science BIO.3B.2

ScienceGrades 9–12Biology

The Standard

BIO.3B: Students will analyze and interpret data collected from probability calculations to explain the variation of expressed traits within a population.

Apply Mendel’s law of independent assortment to interpret dihybrid crosses.

2026 Mississippi College- and Career-Readiness Standards for Science · Reproduction and Heredity

Teacher's field guide

What Students Need to Do: Students list the four gametes a parent with two heterozygous genes can make. They use those gametes to predict offspring traits when the genes assort independently.
What Mastery Looks Like: Given AaBb × AaBb, students write AB, Ab, aB, and ab for each parent. They use a Punnett square to find the 9:3:3:1 trait ratio and explain where it comes from.
Common Misconceptions: Students may think A must always travel with B, or write AaBb as a gamete. They may use the 9:3:3:1 ratio for any two traits, even when the genes are linked or the parents are not both heterozygous.
How to Assess It: Exit ticket: For AaBb × AaBb, list each parent's gametes, give the expected trait ratio, and explain why an Ab gamete is possible.

Lesson moves

Give pairs coins labeled A/a and B/b; have them flip both 40 times and tally the four gametes.
Show an AaBb parent card and ask, 'Why can this parent make an Ab gamete?' Have students write one sentence.
Give pairs AB, Ab, aB, and ab cards for each parent; fill a 4-by-4 Punnett square and tally offspring traits.
A seed grower crosses RrYy pea plants, with R round and Y yellow; predict how many of 160 seeds are wrinkled and green.

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