Reproductive systems and Animal Development

Asexual Reproduction Binary fission Budding, fragmentation Sponges, cnidarians, flatworms, annelids, echinoderms Parthenogenesis – unfertilized egg develops into a complete individual, pg731

Sexual reproduction Egg of one parent is fertilized by the sperm of another. Dioecious – 2 sexes Monoecious – hermaphrodites, few undergo self-fertilization, most cross fertilization Oviparous – Ovoviviparous – Viviparous -

Advantages of Asexual vs Sexual More offspring identical to parent Sexual Beneficial gene combinations that arise through recombination that speed up adaptation in a changing environment Can rid a population of harmful genes more easily.

Hermaphroditism – each individual has both male and female reproductive systems – donates and receives sperm Example: earthworms, sea slugs Internal fertilization – sperm deposited in or near female reproductive tract, fewer gametes and zygotes produced External fertilization – females release eggs into environment, male then fertilizes them, release of gametes by environmental cues, pheremones

Male Reproductive System Testes – produce sperm and sex hormones Epididymis – maturation of sperm Vas deferens – store sperm Seminal vesicles – contribute most fluid to sperm Prostate gland – contribute fluid Urethra – conduct sperm and urine Bulbourethral gland – little fluid to sperm penis

Sperm: hundreds of millions produced each day Spermatogenesis –production of sperm 3 parts Head – nucleus covered by a cap (acrosome) Middle piece – mitochondria (energy) and microtubules Tail – microtubules Takes 7 weeks for 1 sperm to develop Testosterone – main male sex hormone

Female Reproductive System Ovaries – produce ovum and hormones Oviduct (fallopian tubes) – conduct egg, fertilization Uterus – houses embryo during development Vagina Oogenesis – development of mature eggs Immature eggs form in embryo, do not complete development until fertilization

Fertilization

Cellular stages of development Cleavage – cell division without growth Cells get smaller with each division Morula – ball of cells (16) Blastula forms a hollow ball of cells, fluid filled cavity – blastocoel when sodium leaves morula

Tissue stages of development Early Gastrula – cells invaginate into the blastocoel forming the blastopore (protostomes – mouth, deuterstomes – anus) Early gastula has 2 layers of cells, Ectoderm – outer layer Endoderm – primitive gut Late gastrula – mesoderm forms Gastrulation complete

Embryonic Germ Layers Ectoderm – nervous system, epidermis of skin Mesoderm – musculoskeletal system, dermis of skin, cardiovascular system, urinary system, lymphatic system, reproductive system, outer layers of respiratory and digestive systems Endoderm – lining of digestive tract and resp. tract, glands, thyroid/parathyroid glands

Developmental processes Development requires Growth Cellular differentiate – cells become specialized Morphogenesis- shape and form of body