PHL243H1 Chapter Notes -Parthenogenesis, Asexuality, Zygote
Document Summary
Individual starts from a single cell (zygote) formed by two sex cells coming together (gametes) Gametes usually only have one set of chromosomes and the zygote contains two sets of chromosomes so the baby will contain genes from both parents. In reproduction, one cell divides into two, while in sex, two cells fuse to form one. Sex is unnecessary for reproduction since organism can reproduce asexually. Some species consist just of females reproducing daughters genetically identical to themselves, particularly plants but also some animals, although there are no mammals or birds that produce parthenogenetically in this way. It thus can"t be said that without sex reproduction is impossible. In animals and humans, we associate sex with sexual difference males have sperm and females eggs, but in hermaphrodite species like some snails, the same animal produces eggs and sperm. There is a twofold advantage of parthenogenesis, and thus a twofold cost of sex.
