Every new organism gets its genes from its parents. But some organisms have one parent, and some have two. That one difference decides whether the offspring are copies or mixes.
Key idea
One parent: a bacterium splitting in two, a yeast cell budding, a strawberry plant sending out a runner, a plant grown from a cutting. The offspring get an exact copy of the parent's genes. Two parents: each parent passes on half of its genes (one of each pair), so the offspring get a new mix and vary.
Why it works
Genes come in pairs, one of each pair from each parent. A parent with two different versions of a gene can pass on either one, with equal chances. Each offspring gets its own random pick from each parent, for thousands of genes at once. So brothers and sisters share many genes but almost never the same set.
Worked example: Copy or mix?
A gardener wants new plants exactly like her prize-winning rose. Should she plant its seeds or root cuttings?
- Seeds come from pollination, so they get genes from two parents: a new mix.
- A cutting is a piece of the plant itself: one parent, the same genes.
Answer: Root cuttings.
Worked example: Trade-offs
Why might a population with two-parent offspring do better when a new disease arrives?
- Copies all share the same genes, so a disease that harms one can harm all.
- Mixed offspring vary; some may resist the disease.
Answer: Variation makes it more likely that some survive.
Common mistake
Students think offspring of two parents get a blend of every trait, like mixing paint. Each parent passes on one of each pair of genes, and the genes stay whole. That is why siblings can differ from each other, and why a trait hidden in both parents can show up in a child.