Sexual reproduction

Lore & Background

Sexual reproduction involves a life cycle where diploid precursor cells undergo meiosis to produce haploid gametes. During meiosis, homologous chromosomes pair and exchange genetic information through recombination, increasing genetic diversity. Two haploid gametes then fuse during fertilization to form a diploid zygote, which develops via mitosis. In plants, alternation of generations occurs between a haploid gametophyte and a diploid sporophyte.

Reader's Guide

The evolution of sexual reproduction is considered paradoxical because asexual reproduction allows faster population growth, with a 50% cost in fitness. However, sexual reproduction provides advantages such as increased genetic diversity, reduced accumulation of deleterious mutations, and faster adaptation to changing environments. Larger populations appear to benefit more from these advantages. Sexual selection, a mode of natural selection, drives the evolution of traits like peacock tails and lion manes, as individuals compete for mates. Sexual reproduction is widespread across animals, including insects, mammals, and fish, with diverse strategies such as internal fertilization, egg-laying, and live birth.

Did You Know?

• The first fossilized evidence of sexual reproduction in eukaryotes is from the Stenian period, about 1.05 billion years old.
• Sexual reproduction does not occur in prokaryotes, but bacterial conjugation, transformation, and transduction are considered analogous.
• In placental mammals, sperm exit through the male urethra and enter the vagina during copulation, while egg cells enter the uterus through the oviduct.
• Some fish species are hermaphrodites, where a single fish can produce both eggs and sperm.