BIOL 211 Lecture Notes - Lecture 3: Blastomere, Polyspermy, Blastula
Document Summary
Occurs primarily in unicellular or invertebrate animals (found in some vertebrates) 4 basic methods of assexual reproduction occur. Binary fission- animal splits apart (unicellular organisms) A hydra)- offspring are usually smaller and create a new organism off of themselves. Fragmentation (ex sponges)- a piece breaks off and creates a new. Gemmulation (in freshwater sponges, rare)- packets of cells form inside the parent animal and break out into a new animal. All genes get passed on (good and bad) Dioecious means separate sexes on separate animals. Monoecious means one animal is both sexes (hermaphrodite) Mutations get mixed up and do not spread as quickly. Simultaneous (is both sexes at the same time) v. sequential (changes from one sex to another) No male fertilization however there may be males around. Prevent polyspermy (multiple sperm fertilizing one egg)- there would be too much genetic dna. Fast block- a change in the membrane potential. Done by increasing calcium ions inside the egg.