Reproduction and inheritance for O-Level Biology (SEAB 6093): chromosomes, genes and DNA, mitosis and meiosis, sexual reproduction in humans and flowering plants, and monohybrid inheritance and variation

What this module covers

Reproduction and inheritance explains how genetic information is stored, passed on and expressed. In O-Level Biology (SEAB 6093) you must describe chromosomes, genes and DNA and the roles of mitosis and meiosis, explain sexual reproduction in humans and flowering plants including the adaptations of the gametes, and use genetic diagrams to predict the inheritance of a single gene, as well as explain variation. The skill of drawing a clear genetic cross is examined every year.

This overview links every dot point in the module; work through them, then test yourself at the end. See the full set at /sg-o-level/biology/syllabus.

Chromosomes, genes and DNA

Start with where the information sits. The page on cell division and chromosomes sets out the link between DNA, genes and chromosomes and the roles of mitosis (growth and repair) and meiosis (making gametes). Keep the levels clear: DNA is the molecule, a gene is a length of DNA coding for one characteristic, and a chromosome carries many genes.

Sexual reproduction in humans

Next, how new humans are made. The page on sexual reproduction in humans describes the male and female gametes and their adaptations, the meaning of fertilisation, and why sexual reproduction produces variation. Learn the sperm and egg adaptations as paired lists, since "explain how the gamete is adapted" is a frequent question.

Sexual reproduction in plants

Then the plant version. The page on sexual reproduction in plants describes the parts of a flower, the difference between insect and wind pollination, and the steps of pollination and fertilisation. The insect-versus-wind comparison is a classic adaptation question.

Monohybrid inheritance and variation

Finally, predicting offspring. The page on monohybrid inheritance and variation covers the key genetics terms, how to set out a genetic cross to predict offspring ratios, and the difference between continuous and discontinuous variation. The genetic diagram is a method you must be able to lay out cleanly.

How this module is examined

• Keep the levels clear. DNA, gene and chromosome are different things; questions reward the correct relationship between them.
• Adaptation with reason. Gamete questions reward linking each feature to its role (a tail to swim, mitochondria for energy).
• Compare pollination. Give two contrasting features for each of insect and wind pollination.
• Lay out the cross. Genetic diagrams reward defined symbols, correct parent genotypes, gametes, and the final ratio.

Check your knowledge

A mix of recall, application and genetics-diagram questions. Attempt them, then check against the solutions.

1. State the relationship between a gene and a chromosome. (2 marks)
2. State two differences between mitosis and meiosis. (2 marks)
3. Give two ways the sperm cell is adapted to its function and explain each. (2 marks)
4. A heterozygous tall pea plant (Tt) is crossed with a short plant (tt). Use a genetic diagram to give the expected ratio of offspring. (3 marks)