Week 11 — Readings & Resources · Mendelian Genetics

Course: Introduction to Biology — General Biology I (BIOL 101) · Silver Oak University (fictional sample) · Prof. Castellano
Objective covered: Objective 6 — Use Mendel's laws of segregation and independent assortment, with Punnett squares and probability, to predict offspring genotypes and phenotypes.

How to use this page

Everything here is a link to an external resource — open it in your browser, the same way you'd open a YouTube link. Nothing needs to be downloaded.

This week's load is deliberately light: 2 short videos + 2 short readings, grouped by the ideas from the lecture, plus a couple of optional free references. Watch or read one item per group and you're ready for the quiz; do all of them and you'll be very comfortable. Total time is roughly 35–45 minutes if you do everything, far less if you pick one per group.

Order that matches the lecture: ① vocabulary + segregation → ② the monohybrid Punnett square & probability → ③ the dihybrid cross & independent assortment.

A habit to start now: before you trust any genetics claim — in these resources, from a classmate, or from a chatbot — re-draw the Punnett square and re-do the fraction yourself. Genetics is exactly where confident-sounding sources get the ratio wrong.

① Vocabulary, Mendel & the Law of Segregation

Maps to Lecture Segments 2–3. Lock the four vocabulary pairs (gene/allele, dominant/recessive, genotype/phenotype, homozygous/heterozygous), then Mendel's big idea: each parent passes just one allele per gene.

Video — "Heredity: Crash Course Biology #9" (CrashCourse)
🔗 https://www.youtube.com/watch?v=CBezq1fFUEA
Why it earns the click: a fast, funny tour of exactly this week's foundation — Mendel and his peas, dominant vs. recessive, genotype vs. phenotype, and how a Punnett square predicts offspring. It lands the same point we made in class: a recessive allele can hide in a heterozygote and reappear later.
⏱ ~11 min

Reading — "Mendel's Experiments and the Laws of Probability" (OpenStax Biology 2e, §12.1)
🔗 https://openstax.org/books/biology-2e/pages/12-1-mendels-experiments-and-the-laws-of-probability
Why it's assigned: the cleanest plain-language version of Mendel's monohybrid results, the 3:1 ratio, and the product and sum rules of probability we used to get 1/4 and 9/16 — free to read online, no account needed. Read through "The Product Rule and Sum Rule."
⏱ ~12 min

② The Monohybrid Punnett Square & Probability

Maps to Lecture Segments 4–5. The heart of the week: set up a Tt × Tt cross, fill all four boxes, read the 1:2:1 genotype and 3:1 phenotype ratios, and use the product rule for P(recessive) = 1/4.

Video — "Monohybrids and the Punnett Square Guinea Pigs" (Amoeba Sisters)
🔗 https://www.youtube.com/watch?v=i-0rSv6oxSY
Why it earns the click: a friendly, step-by-step walkthrough of a monohybrid cross with hairless guinea pigs — the exact skill from Segment 4. They list the gametes, fill every box, and read the genotype and phenotype ratios right off the square, just like we did on the board.
⏱ ~8 min

Reading — "Probabilities in Genetics" (Khan Academy, Classical Genetics)
🔗 https://www.khanacademy.org/science/biology/classical-genetics/mendelian--genetics/a/probabilities-in-genetics
Why it's assigned: shows why a Punnett square and the product rule give the same answer, and how to compute the odds of a specific genotype without drawing a giant grid — the "multiply for and" move from Segment 5. Free to read online.
⏱ ~8 min

③ The Dihybrid Cross & Independent Assortment (9:3:3:1)

Maps to Lecture Segment 6. The line to carry out of this week: a dihybrid 9:3:3:1 is just two independent 3:1 crosses multiplied together (3/4 × 3/4 = 9/16; 1/4 × 1/4 = 1/16).

Reading — "The Law of Independent Assortment" (Khan Academy)
🔗 https://www.khanacademy.org/science/ap-biology/heredity/mendelian-genetics-ap/a/the-law-of-independent-assortment
Why it's assigned: explains why alleles for different genes are inherited independently and walks the dihybrid cross to the 9:3:3:1 phenotype ratio — the same logic we used to get P(both dominant) = 9/16 and P(both recessive) = 1/16. Free to read online.
⏱ ~10 min

Optional one-stop references (free online)

• Learn.Genetics (University of Utah) — "What Are Dominant and Recessive?" A clear, myth-busting page on what dominant/recessive really mean — including the big Week-11 correction that dominant does NOT mean more common (recessive light-eye alleles are the majority in Scandinavia). A great reality check on the vocabulary.
  🔗 https://learn.genetics.utah.edu/content/basics/patterns
• OpenStax Biology 2e, §12.2 "Characteristics and Traits." Goes deeper on genotype vs. phenotype, homozygous vs. heterozygous, the test cross, and dihybrid crosses, with worked Punnett squares. Free to read online — a good place to return to all week.
  🔗 https://openstax.org/books/biology-2e/pages/12-2-characteristics-and-traits

Pick-one quick path (≈19 min total)

In a hurry? Do exactly these two and you'll be ready for the quiz:
1. Watch "Monohybrids and the Punnett Square Guinea Pigs" (group ②) and fill one Tt × Tt square yourself.
2. Skim "Mendel's Experiments and the Laws of Probability" through the product rule (groups ① and ③).

Heads-up (links rot): these point to outside sites that occasionally move or rename pages. If a link ever fails, tell Prof. Castellano and use the OpenStax or Khan Academy references above in the meantime.