Class 10 Science Chapter 8 Revision Notes

Class 10 Science Chapter 8 – Heredity: Revision Notes

Heredity: transmission of traits from parents to offspring across generations.
Gene / Allele: a gene is a unit of heredity; alleles are alternative forms of a gene (e.g. T for tall, t for short).
Genotype vs Phenotype: genotype = genetic makeup (e.g. Tt); phenotype = observable trait (e.g. tall).
Homozygous vs Heterozygous: homozygous = both alleles same (TT or tt); heterozygous = alleles differ (Tt).
Dominant vs Recessive: dominant allele expresses even in heterozygous condition; recessive expresses only when homozygous.
Monohybrid cross F2 ratio: 3 (dominant) : 1 (recessive); genotypic 1:2:1.
Dihybrid cross F2 ratio: 9:3:3:1.
Sex determination in humans: XX = female, XY = male; father’s sperm (X or Y, 1:1 ratio) determines the child’s sex.
Variation: differences arising during reproduction/DNA copying; provides the raw material for a species to survive environmental change.
Acquired vs inherited traits: only germ-cell (egg/sperm) DNA changes are inherited; somatic changes from lifestyle are not passed on.
Syllabus note (2023 rationalisation): the Evolution section of the earlier “Heredity and Evolution” chapter has been removed; this chapter is titled simply “Heredity”.