Week 11 — Mendelian Genetics

Why this matters

A nursing student explaining how a family's traits pass from parents to children and a gardener deciding which two plants to cross both use this week's odds.

In plain language

Children often look a little like each parent, and sometimes a trait seems to skip a generation and come back. This week you learn the rules that explain it, rules Gregor Mendel worked out with garden peas and published in 1866. Each parent hands down one allele (one version of a gene) for each trait, and chance decides which one. With a simple grid called a Punnett square (a table that lists every way the parents' versions can combine), you can predict the odds of each kind of offspring before any are born. You will also see why those odds describe many offspring well and one small family poorly.

• Already covered: Week 10 showed how meiosis splits each chromosome pair into gametes.
• This week: alleles, Mendel's two laws, Punnett squares, the product and sum rules, and the test cross.
• How they connect: Mendel's laws are what meiosis does to alleles.
• Where we're going next: Week 12 bends Mendel's simple rule.

Focus

Given two parents, what are the odds of each kind of offspring?

By the end of this module, you should be able to:

• [ ] tell genotype from phenotype, and dominant from common
• [ ] fill a Punnett square for Tt × Tt and read both ratios
• [ ] use the product rule and the sum rule on a cross
• [ ] read a test cross and a two-gene cross

To-do

Plan your week

1. Read Chapter 11 (about 45 minutes), then the lecture and slides.
2. Work the lecture tutorial (60–90 minutes) and the practice set (20 minutes).
3. Run the Biology Lab & Inquiry (2 hours), then the discussion and assignment.
4. Take the quiz.

This week's checkpoint: fill a Punnett square for two Tt parents and give the genotype and phenotype ratios.

You've got this

Take it in order; ask your instructor if a step snags.

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