Much of what we know about inheritance was first worked out in fruit flies and corn. Both let you watch real traits pass from parents to offspring, with no lab beyond a bench and a magnifier.
Why fruit flies
Drosophila melanogaster breeds fast, lives happily in a small vial, and comes in dozens of mutant strains with traits you can see.
It has four pairs of chromosomes. Pair 1 is the sex chromosomes, X and Y, so the same flies can show both ordinary and sex-linked inheritance.
Traits you can see
These mutant strains are a common starting set because each trait is easy to spot under a stereo microscope or a hand lens.
white: white eyes. Chromosome 1, so it is sex-linked.
apterous: no wings. Chromosome 2.
vestigial: tiny, crumpled wings. Chromosome 2.
ebony: a black body. Chromosome 3.
sepia: dark brown eyes. Chromosome 3.
Wrinkled: wrinkled wings, a dominant trait. Chromosome 3.
Running a cross
A cross through two generations takes a little over five weeks, and warmer or cooler rooms shift the timing.
The night before: clear every adult out of the parent vials. Females store sperm after mating, so only flies that hatch overnight are guaranteed unmated.
Day 1: put about 6 males of one strain and 6 unmated females of the other into a fresh vial of medium.
Days 7 to 10: remove the parents, so they cannot mate with their offspring.
Days 12 to 14: the first generation (F1) hatches. Move some into new vials to breed with each other.
Days 21 to 24: remove the F1 flies.
Days 26 to 28: the F2 generation hatches. Start counting the day after the first ones appear, and never put counted flies back.
The sex-linked cross worth doing first
Cross white-eyed females with wild-type males. Every son inherits his X chromosome from his mother, so the sons have white eyes while the daughters have red eyes, a pattern you can see on the first day of counting.
Genetic corn
A genetic corn ear is a whole Mendelian experiment already grown for you. Every kernel is one offspring, and its color and shape show which alleles it inherited.
Carolina's dihybrid ear comes from a cross of purple starchy (R/R Su/Su) with yellow sweet (r/r su/su) parents. On the second-generation ear the kernels fall close to 9 purple starchy to 3 purple sweet to 3 yellow starchy to 1 yellow sweet. Sweet kernels dry wrinkled, which makes them easy to tell apart.
Count one row at a time and mark your starting kernel with a pin. Kept dry, an ear lasts for years.
A stereo microscope for sorting flies
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Stereo zoom, trinocular
AmScope SM-4TZ-144A stereo zoom microscope
Trinocular stereo zoom microscope on a double-arm boom stand, with a 144-LED ring light and Barlow lenses for 3.5X to 90X. The eyepiece tubes are 30 mm and the photo tube is 23 mm.