The unit in one line
What genes are made of and how they are copied and read, how traits pass from parents to offspring, and what happens when genes or chromosomes change. 6 of Botany's 40 questions over five chapters, many of them worked crosses.
Read in this order
- Genetic material (9 min) — DNA and RNA structure, semi-conservative replication, the central dogma and the genetic code.
- Mendelian genetics (9 min) — the terms, the laws, monohybrid and dihybrid crosses, incomplete and co-dominance. Keep the Genetics ratios cheat sheet open beside it.
- Linkage and crossing over (8 min) — why some genes do not assort independently, and how a recombination frequency becomes a map distance.
- Sex-linked inheritance (9 min) — X-linked patterns, colour blindness and Morgan's white-eyed Drosophila.
- Mutation, polyploidy and genetic disorders (9 min) — gene and chromosomal mutations, polyploid crops, and the six disorders MEC names with their causes.
About 45 minutes in all. If meiosis is hazy, read Cell cycle and cell division first: every ratio here follows from it.
How it is asked
MEC sets the paper roughly half recall, a third understanding and a fifth application. Recall here is codons, scientists and dates, and the karyotype of each syndrome. Understanding is why a test cross reveals a genotype, or why colour blindness is commoner in men. Application is a cross with stated phenotypes to solve, a pedigree to read, or a recombination frequency to turn into map units.
Then practise
Each chapter has a fixed-length chapter test under Practice › Topics, drawn from questions written to that chapter's scope. Sit it after reading; a second sitting a week later shows whether it stuck.