Sexual Reproduction

Sexual reproduction involves the fusion of two compatible gametes (sex cells), one contributed by each parent, and every organism must first reach reproductive maturity before it can reproduce this way. In plants, the transition out of the purely vegetative or juvenile phase and into the reproductive phase is most visibly marked, in higher plants, by the onset of flowering.

The flower is the specialised reproductive organ of a flowering plant, built specifically to produce haploid gametes and to give those gametes the best possible chance of fertilizing successfully. A typical, complete flower is organised into four concentric whorls: the calyx (sepals), the corolla (petals), the androecium (the male whorl of stamens), and the gynoecium (the female whorl of carpels).

Unlike asexual reproduction, sexual reproduction is built around two pivotal events: meiosis, which halves the chromosome number to produce haploid gametes, and the subsequent fusion of a male and a female gamete to reconstitute a diploid zygote. Because the two parental gamete genomes combine and recombine, the resulting offspring are genetically dissimilar both from each other and from their parents, a source of variation that is essential raw material for natural selection and the long-term evolution of a species. …