Inheritance questions ask how a trait passes from parents to offspring and what ratios to expect. This hub gathers the skills and a practice set for crosses and pedigrees.
It belongs to the SPM Biology guide. Variation between offspring links to variation.
What does the cluster cover?
Each lesson handles one step in reasoning about a trait.
- Using allele, genotype and phenotype terminology: the vocabulary that every cross needs.
- Completing monohybrid crosses: from parents to a stated ratio.
- Interpreting sex-linked inheritance: when the gene is on the X chromosome.
- Reading pedigrees without making personal genetic claims: using a family diagram as evidence.
A second set of lessons, inheritance evidence rather than family assumptions, goes deeper into what a cross or pedigree can and cannot show.
How do the skills connect?
Terminology names the parts, and the monohybrid cross combines them. Sex-linked inheritance adds one twist, and pedigrees work backwards from offspring to the likely genotypes of their parents.
Taken in order, they move you from naming to predicting to working backwards.
One example: one trait, one ratio
Take an invented plant whose stem is either tall or short. Tall (T) is dominant and short (t) is recessive. Two tall plants that both carry the short allele are crossed, so the parents are Tt × Tt.
Each parent makes T gametes and t gametes in equal numbers. The offspring are TT, Tt, Tt and tt, which gives three tall plants for every short one. That 3:1 is an expected ratio, not a promise for a small sample.
Where should you start?
If you confuse allele and gene, or genotype and phenotype, begin with terminology. If your ratios are wrong, start with monohybrid crosses. Students who freeze at family diagrams should start with pedigrees or the evidence lessons.
When you finish, try the practice set and build crosses in the simple inheritance cross explorer. For teacher support, see online one-to-one Biology tuition.