Worksheets › Class 10 › Heredity › Cheat sheet
Class 10 Heredity: cheat sheet
CBSE Science. How traits pass from parents to offspring: Mendel's experiments, dominant and recessive traits, ratios, and sex determination.
Key ideas
- Each trait is controlled by a pair of genes, one from each parent.
- A dominant trait shows even with one copy of its gene; a recessive trait shows only with two copies.
- Mendel crossed pure tall and dwarf pea plants: all of the first generation were tall, and the second generation was 3 tall : 1 dwarf.
- With two traits, the second generation shows a 9 : 3 : 3 : 1 ratio, so the traits are inherited independently.
- Genes are on chromosomes; each gamete gets one gene of each pair.
- Humans: females are XX and males XY. The father’s sperm (X or Y) decides the sex of the child.
Remember
| Monohybrid cross | Tt × Tt → TT : Tt : tt = 1 : 2 : 1; tall : dwarf = 3 : 1 |
| Dihybrid ratio | 9 : 3 : 3 : 1 |
| Sex determination | XX × XY → half XX (girl), half XY (boy) |
Watch out
- Saying the mother decides the sex of the child.
- Mixing up the 3 : 1 (what they look like) and 1 : 2 : 1 (gene pairs) ratios.
- Thinking a recessive trait disappears for ever (it can reappear in later generations).
Worked example
Cross iiGg with iiGg (I = inflated, i = constricted; G = green, g = yellow). List the kinds of offspring (phenotypes) and give their ratio. Show the working for each trait separately.
Working: pod shape: all constricted; pod colour: 3 green : 1 yellow; multiply
Answer: constricted green pods : constricted yellow pods = 3 : 1
Practise Heredity
Revise with this page, then practise: every Heredity sheet in the app is new, with an answer key and working.
Coming soon for Android and iPhone.