Cell division and inheritance explains how cells copy themselves, how sex cells are made, and why offspring resemble their parents without being identical to them. In IGCSE Biology it follows human reproduction and development and leads into variation and selection.
This page gives you the route through the five lessons, one orienting example and the traps that cost marks. The genetics here is academic and uses invented organisms, so it never predicts anything about a real family.
What should you know before starting?
- Cells have a nucleus that holds the genetic material. Chromosomes are found in the nucleus.
- Sexual reproduction joins two gametes. One comes from each parent.
- Simple fractions. Out of 4, 2 is one half, and 1 is one quarter.
- Dominant and recessive as words, even if you are not yet sure how they work.
If the gamete idea feels thin, the human reproduction module covers fertilisation first.
One orienting example
Question: A plant cell has 8 chromosomes. State how many chromosomes are in each cell after mitosis and after meiosis.
After mitosis there are two cells, each with 8 chromosomes, identical to the parent cell. After meiosis there are four cells, each with 4 chromosomes, and they are genetically different from each other.
Now add a cross. Two purple plants with alleles Rr give RR, Rr, Rr and rr in the grid.
Three of the four offspring are purple and one is white, so the probability of a white offspring is 1/4 (25%). The answer used chromosome halving, alleles, genotype, phenotype and probability. The five lessons train each of those separately first.
In what order should you study the lessons?
- Compare the chromosome outcomes of mitosis and meiosis: the number of cells and the chromosome count in each.
- Distinguish gene, allele and chromosome: three words that are easy to swap.
- Construct a simple inheritance grid: gametes along the first row and column, offspring inside.
- Separate genotype from phenotype: what the alleles are versus what can be seen.
- Explain probability across repeated offspring: why a 3 to 1 ratio is a chance, not a promise.
Finish with the mixed practice set. The inheritance model board and the probability tree and counting board let you test a cross in a fictional model.
What traps catch students?
- Saying meiosis makes identical cells. It makes genetically different cells with half the chromosomes.
- Writing “a gene is a version of an allele”. It is the other way round.
- Writing the phenotype in a genotype box. Rr is a genotype, purple is a phenotype.
- Treating 1 in 4 as a certainty. Each offspring has that chance independently.
How should you use the practice set?
Attempt each question on paper before opening the answer. Mark yourself on the working, not only the final number. Then use the routing section at the end of the set to choose which lesson to reread.
Some students can draw a perfect grid but lose marks on the sentence that follows it. That gap is something a teacher in online one-to-one Biology tuition can spot quickly, and the full list of modules sits in the Biology learning guide.