Asexual or Sexual Reproduction: Fast Copies or New Variety

0:00Living things reproduce asexually or sexually. Is one way simply better?

0:06Asexual reproduction needs only one parent.

0:10Each offspring is a clone: it has the same genes as its parent, apart from rare mutations.

0:17No mate is needed, so numbers can grow fast: four, then eight.

0:24So the population has very little variety.

0:27Sexual reproduction usually needs two parents.

0:31Each parent makes sex cells, called gametes, by a cell division called meiosis.

0:38Meiosis halves the number of chromosomes and shuffles the genes, so gametes carry different mixes.

0:45At fertilization, two gametes, one from each parent, join to make a fertilized egg.

0:52Each fertilized egg grows into an offspring with a new mix of genes.

0:57This is slower, so there are fewer offspring, but they are varied.

1:03Now a new disease arrives.

1:06All the clones share the same genes, so one disease could wipe them all out.

1:12With variety, some offspring may have genes that help them resist it, so they survive.

1:20So neither way is simply better: fast copies suit steady conditions, and variety helps when things change.

1:29Some species use both. Strawberry plants send out runners that grow into clones, and their flowers make seeds.

1:37Many aphids clone themselves in summer, then mate and lay eggs in the fall.

1:44Asexual reproduction makes fast copies, and sexual reproduction makes new variety.