Asexual - based on mitotic cell division - offspring genetically similar to parent - advantageous in stable & favorable environment

Sexual - based on meiotic cell division -involves fusion of sperm & eggs - offspring genetically different from parents - advantageous in changing environment

Fission - separation of parent into 2 or more individuals of similar size - invertebrates

Budding - new individual splits off existing one - cnidarians & many other invertebrates

Fragmentation - body of parent fragments - new individuals develop from fragments - must be accompanied by regeneration - many invertebrates

Parthenogenesis - egg develops without fertilization - adult haploid - common in invertebrates, some vertebrates

Hermaphroditism - each individual has both male and female reproductive organs - invertebrates

Sequential hermaphroditism - sex changes during lifetime - certain fishes

Involves union of gametes - syngamy - to produce zygote

Gametes haploid - zygotes usually diploid

External fertilization - eggs shed by female prior to fertilization - usually in moist environment - usually many zygotes

Internal fertilization - requires complex cooperative behavior - fewer zygotes - parental protection

Spermatogenesis - occurs in males - production of sperm

Oogenesis - occurs in females - production of ova (eggs)

Both involve meiotic cell divisions

Primary spermatocytes produced throughout life of male

One primary spermatocyte produces four spermatids

Spermatogenesis occurs continuously

All primary oocytes present at birth of female

One primary oocyte produces one ovum

Characterized by long "resting" periods in which no production occurs