1 / 29

Chapter 46: Animal Reproduction

Chapter 46: Animal Reproduction. Asexual reproduction Offspring from one parent; growth by mitosis Types Fission- equal division of cytoplasm (ex. Bacteria, paramecia) Budding- unequal division of cytoplasm (ex. Cnidarians, yeast colonies, gemmule production in Porifera)

bianca-mccray
Download Presentation

Chapter 46: Animal Reproduction

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 46: Animal Reproduction Asexual reproduction Offspring from one parent; growth by mitosis Types Fission- equal division of cytoplasm (ex. Bacteria, paramecia) Budding- unequal division of cytoplasm (ex. Cnidarians, yeast colonies, gemmule production in Porifera) Fragmentation- body broken into pieces Regeneration of lost parts Found in sponges, cnidarians, annelids, tunicates, & enchinoderms Advantages Isolated individuals can reproduce without a mate Less time between generations Successful genotypes perpetuate

  2. Sexual reproduction • 2n offspring (zygote) produced by the fusion of egg & sperm • Gametes formed by meiosis • Female gamete=ovum • Male gamete=sperm • Offspring have characteristics of both parents resulting in species variation • Reproductive cycles & patterns vary among animals • Often seasonally based & controlled by hormones • Parthenogenesis • Development of an unfertilized egg into new individuals • Ex. Aphids, bees, daphnia • Hermaphrodites • Individuals have functioning ovaries & testes • Self fertilization is rare • Found in slow moving, energy conserving organisms • Sequential hermaphrodites • Individual reverses its sex • Ex. Some fish & oysters

  3. Mechanisms of sexual reproduction • External fertilization • Occurs in moist habitats to prevent desiccation & heat stress • Environmental cues & pheromones trigger release of gametes • Vertebrates (fish, amphibians) exhibit courtship behavior to ensure fertilization • Large numbers of zygotes result • few reach sexual maturity • Gelatinous coat covers the egg to permit gas & H2O exchange

  4. Internal fertilization • Fewer zygotes produced but more parental protection • Requires • Cooperative behavior • Copulatory organ for sperm delivery & a sperm receptacle for storage/transport • Mating behaviors to signal copulatory receptivity • Adaptations include • Shelled egg (“pond away from the pond”) in egg laying animals • Reptiles & monotremes- amniotic egg with protein shell • Birds- amniotic egg with calcium shell • Mammals have internal embryonic development • Marsupials- embryo in uterus for short time; completes development in maternal pouch • Eutherians (placental)- embryo in uterus until development complete

  5. Reproductive system complexity is not necessarily an indicator of phylogenetic relationship • Parasitic flatworms reproductive system is one of the most complex • Polycheates have separate sexes without distinct gonads • Insects have separate sexes & complex reproductive tracts; females can store sperm for years after a single mating in the spermatheca • Vertebrates have similar reproductive systems with some differences • Mammals have separate openings for digestion, excretion, & reproduction • Non-mammals have single opening=cloaca • Some mammals, birds, & snakes have a single branched uterus; most mammals have a divided uterus • Non-mammalian vertebrates do not have well developed penises & use other means to transfer spermatozoa

  6. Mammalian Reproduction • Human male • Testes develop & descend from the abdomen into the scrotum • Sperm production requires a lower temperature • Penis is copulatory organ; ejaculatory duct joins urethra • Human female • More complicated than the male • Produces female gamete • Houses embryo & developing fetus for gestation period

  7. Human Sexual Response Cycle • Coitus= sexual intercourse • Excitement • Vasocongestion of penis & clitoris (increased arterial blood flow) • Myotonia- muscle tension • Plateau • Stimulation of autonomic nervous system • Orgasm • Rhythmic involuntary contractions of reproductive structures in both sexes • Resolution • Reverses early responses

  8. Meiosis • Spermatogenesis • All 4 cell products become mature spermatozoa • Continuous process; 100 million +sperm/day • Oogenesis • Unequal cytokinesis results in one ovum & 3 polar bodies • All potential ova present at birth as primary oocytes in the ovaries

  9. Males • Androgens (testosterone) produce primary & secondary sex characteristics • GnRH from hypothalamus stimulates anterior pituitary to release LH & FSH • LH- stimulates testosterone production • FSH- stimulates sperm production in seminiferous tubules • Females • Estrogen produces primary & secondary sex characteristics • Estrous cycle occurs in non-primate mammals • “heat”; period of sexual activity surrounding ovulation • Ovulation occurs after thickening of endometrium • Menstrual cycle in primates & humans • Menstruation- shedding of endometrium • Proliferative phase- regeneration of endometrium • Secretive phase- endometrium thickens & vascularizes • Follicle phase- egg matures in follicle • Ovulation- egg is released • Corpus luteum phase- follicle fills with yellow tissue mass; secretes progesterone • Menopause- female stops menstruation & ovulation; ovaries no longer respond to LH & FSH • Gestation period (conception to birth) • Humans 266 days (38 weeks) • Rodents 21 days • Cows 270 days • Elephants 600 days • Dogs 60 days

  10. Development • 1st trimester • Conception in oviduct • Cleavage- 24 hours after conception • Implantation of blastocyst (sphere of cells) • HcG secreted by corpus luteum to maintain progesterone • Placenta formation • Organogenesis • 8 weeks= fetus • 2nd trimester • Fetus grows longer- up to 30 cm • Movement detected • Placenta takes over progesterone production so HcG declines as corpus luteum disintegrates • 3rd trimester • Fetus grows to 50 cm • Mass increases rapidly • Maternal organs compressed • Labor • Induced by interplay of hormones estrogen, oxytocin, & prostaglandins • Parturition (birth) • Dilation of cervix • Strong uterine contractions through positive feedback • expulsion

  11. Contraception • Abstinence • Rhythm method • Physical barriers… condoms, diaphragms, cervical caps, sponges • Implants… IUD- spiral shaped device implanted into uterine entrance to prevent sperm entry • Withdrawal • Chemical contraception…prevents release of gametes (pill) • Tubal ligation… closing oviducts • Vasectomy… cutting of vas deferens • Miscarriage…. Spontaneous abortion (1/3 of all pregnancies) • Abortions… 1.5 million/year in US • RU-484… blocks progesterone receptors on uterus so pregnancy is not maintained

  12. Modern technology • Ultrasound • Non-invasive • High frequency sound waves to “picture” fetus • Sampling maternal blood • Used to detect fetal metabolic waste • Amniocentesis • Invasive extraction of amniotic fluid to examine fetal cells • Chorionic villus sampling • Invasive biopsy of placental tissue to detect genetic disorders • In vitro fertilization • “test tube baby” • Mother egg & father sperm fuse in vitro (in glass) after several cleavages embryo is implanted into mother

More Related