Inheritance & Variation

What this lesson covers

Inheritance & Variation is a 7-part O Level Biology lesson. Each part makes one point and then hands over to the next, so it can be read in a sitting or picked up again at the part you stopped on. It defines the idea in plain words before using it, works through an example step by step, breaks the topic into its parts and compares them, names the mistakes that cost marks in an exam, ends with a recap of what to remember.

How it begins

A chromosome is a thread of DNA. A gene is a length of DNA coding for one protein. An allele is a different version of the same gene. Genotype is the alleles present (Tt). Phenotype is the observable characteristic (tall). Homozygous means two identical alleles (TT or tt); heterozygous means two different (Tt). A dominant allele is expressed whenever present, written as a capital.

The 7 parts

1. The vocabulary, which must be exact
2. Mitosis and meiosis
3. Genetic diagrams, laid out for the marks
4. Mutation, natural selection and selective breeding
5. Where marks go
6. What to remember
7. Watch one worked through