Week 12 — Patterns of Inheritance
Why this matters
A nursing student explaining a family's blood types and a gardener wondering why red and white flowers gave pink both use this week's crosses and family charts.
In plain language
Last week's rules work for many traits, but not for every one. Sometimes a child plant is a blend of its two parents, and sometimes a person shows two versions of a trait at the same time. This week you meet those patterns, and you meet the ABO blood types, which come from a gene with three versions in the human population. You also learn why some traits are far more common in men, because the gene sits on the X chromosome (one of the two chromosomes that differ between males and females). Finally, you read a pedigree (a family chart that tracks one trait across generations) the way a genetic counselor does.
- Already covered: Week 11 turned meiosis into Punnett squares and odds.
- This week: blends, both-at-once traits, the ABO blood types, X-linked traits, and pedigrees.
- How they connect: the boxes stay the same; only the heterozygote's look changes.
- Where we're going next: Week 13 shows what a gene is made of.
Focus
When Mendel's simple rule bends, how do we still predict the odds?
By the end of this module, you should be able to:
- [ ] tell incomplete dominance from codominance
- [ ] work a blood-type cross with the ABO alleles
- [ ] work the carrier-mother cross for an X-linked trait
- [ ] read a pedigree with two decisions in order
To-do
Plan your week
- Read Chapter 12 (about 45 minutes), then the lecture and slides.
- Work the lecture tutorial (60–90 minutes) and the practice set (20 minutes).
- Run the Biology Lab & Inquiry (2 hours), then the discussion and assignment.
- Take the quiz.
This week's checkpoint: cross two pink snapdragons and give the color ratio and P(pink).
You've got this
Take it in order; ask your instructor if a step snags.
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