Dihybrid Crosses and Pedigrees and Inheritance | Six Minutes: Biology, Part 17

Six Minutes: Biology, Part 17: Dihybrid Crosses and Pedigrees and Inheritance: Solve two-trait crosses step by step; then Pedigrees and Inheritance A dihybrid cross tracks two genes at once, using four gamete types and a sixteen-box Punnett square. Heterozygous-by-heterozygous crosses give the classic 9:3:3:1 phenotype ratio, which you can verify by multiplying single-trait probabilities. Then: Learn the symbols of a pedigree and the two questions that reveal whether a trait is dominant or recessive, autosomal or X-linked. Then assign genotypes from a family chart and check them with a Punnett square. Chapters 0:00 Introduction 0:23 Two genes at once 1:00 The 4 by 4 square 1:43 Worked example 2:33 Trap 2:59 Recap 3:18 Pedigrees and Inheritance 3:30 Reading the symbols 3:52 Spotting the pattern 4:34 Worked example 5:34 The trap 5:56 Recap 6:13 Thanks for watching Practice problems 1. In a made-up plant, gene T controls height (T = tall, t = short) and gene C controls flower color (C = red, c = white). Cross two plants that are both TtCc. What fraction of offspring should be short with white flowers? Answer: 1/16. 2. Cross a TtCc plant with a ttcc plant. List the gametes of each parent and give the phenotype ratio of the offspring. Answer: TtCc makes TC, Tc, tC, tc; ttcc makes only tc; offspring ratio is 1 tall red : 1 tall white : 1 short red : 1 short white. 3. In a pedigree, two unaffected parents have an affected son and an affected daughter. What inheritance pattern fits, and why? Answer: autosomal recessive, because unaffected parents have affected children and both sexes are affected. 4. Two unaffected parents have three children: one affected, two unaffected. If the trait is autosomal recessive, what are the parents' genotypes and the chance an unaffected child is a carrier? Answer: both Aa; two out of three. Six Minutes @SixMinuteClass: One technique, about six minutes. The narrator's voice is synthetic (computer-generated). Independent educational video. © 2026 Six Minutes · @SixMinuteClass