“Genetic Crosses in Depth” is available to Standard subscribers.
Some crosses give ratios that Mendel's two laws do not predict at first sight, and some data need a test before you trust a ratio. You work out gene interaction, such as epistasis and complementary genes, by listing every cross in Python. You test ratios with chi-square, use the Hardy-Weinberg tool to find carriers, and build gene maps from three-point crosses. It goes beyond the textbook, to the level of A-Level Biology, IB Higher Level and the Olympiad.
3Lessons12Problems2Python Labs1Question Set1Mock Test
Gene interaction and modified ratios: Two genes can act on the same trait. Then the ratio of the F2 is not 9 : 3 : 3 : 1, although the genes still assort independently. This lesson lists every box of the Punnett square and shows how epistasis and complementary genes make the ratios 9 : 3 : 4, 12 : 3 : 1, 9 : 7 and more.
Testing ratios, and carriers in a population: Real counts never match a ratio exactly. The chi-square test says whether the difference is only chance. The Hardy-Weinberg tool turns the number of affected people into the number of carriers. This lesson works both with exact numbers.
Gene maps, trihybrid crosses and pedigree puzzles: A three-point test cross tells you the order of three genes and the distances, and it shows double crossovers. Then you use the product rule for three genes at once, and you solve a pedigree puzzle in which a healthy son changes the chance that his mother is a carrier.