Explain how equal genetic contribution of male and female parents is ensured in the progeny.

When sperm and egg cells are made, each one gets exactly half the chromosomes of a normal cell. When they join during fertilisation, the baby gets exactly half its genes from the mother and half from the father.

Equal genetic contribution from both parents is ensured through meiosis and fertilisation: 1. Normal human body cells are diploid (2n = 46 chromosomes — 23 pairs). Each pair consists of one chromosome from each parent. 2. During gamete formation (gametogenesis), meiosis reduces the chromosome number to haploid (n = 23). Each gamete (sperm or egg) receives only one chromosome from each homologous pair. 3. Meiosis also includes crossing over, where segments of DNA are exchanged between homologous chromosomes, creating new gene combinations — but the DNA quantity is equally halved. 4. During fertilisation, the sperm (n = 23) and egg (n = 23) fuse to form a zygote (2n = 46), restoring the diploid number. 5. Of the 23 pairs in the zygote, 23 chromosomes come from the father's sperm and 23 from the mother's egg. No chromosome is contributed solely by one parent — every pair has one maternal and one paternal chromosome.