Sense organs mitosis and meiosis reproduction

1. Sense organsmitosis and meiosisreproduction BIOL240.002 Zoology 15 September 2014

2. Sense Organs • Receptor cells • Neurons or specialized epithelial cells that connect to neurons • All-or-none electrical impulse based on depolarization of membrane from stimulus • Aggregations (sense organs) create differences in stimulus magnitude via variation in • …frequency of impulse transmission • …number of neurons transmitting • …which neurons transmit and which do not

3. Sense Organs • Mechanoreceptors • Stimulated by kinetic/mechanical energy • Ex: Insect tactile hairs • Ex: Statocyst • Comb jelly • Crayfish • Sphere of ciliated cells with statoliths to register gravity • Iron filings and a magnet can cause a crayfish to orient upside down • Vertebrate (vestibular organ with three semicircular canals in inner ear) Fig. 13.40 p. 270 Fig. 7.32 p. 150

4. HANDOUT—Crayfish Statocyst

5. HANDOUT—Vertebrate Inner Ear

6. Sense Organs Fig. 13.44 p. 272 • Chemoreceptors • Stimulated by odors or tastes • Ex: Insect taste hairs • Ex: Vertebrate tongue receptors • Ex: Vertebrate nasal epithelium Fig. 18.18 p. 379

7. Sense Organs • Thermoreceptors • Sense heat • Ex: Pit organs of some snakes • Electroreceptors • Receive electrical stimuli • Ex: Many fish emit a weak electrical field and sense it as a way of detecting potential danger Fig. 18.19 p. 379 Fig. 16.9 p. 334

8. Sense Organs • Photoreceptors • Stimulated by light wavelengths • May occur diffusely on epidermis • Ex: Earthworms • Ocelli • Simple organs that detect light’s intensity/direction, but do not form images • Ex: Jellyfish • Ex: Flatworm Fig. 8.5 p. 158

9. Sense Organs • Camera Eyes • Retina, lens, and iris • Ex: Cephalopod mollusks • Ex: Vertebrates • Compound Eyes • Ex: Arthropods • Unit: Ommatidium, with seven receptors Fig. 10.34 p. 207 Fig. 13.23 p. 261 HANDOUT

10. Scenes from The Fly (1958)

11. Mitosis • Cell cloning • Nutshell version: Replicate each and every chromosome, make two identical cells, each with its own set of the original • Animalia: In most cases, 2N cells • Cells have homologous pairs, derived from two parents • N is a species-specific characteristic • N = 1 in the Australian bulldog ant • N = 2 in a roundworm used in lab studies • N = 4 in Drosophila fruit flies • N = 7 in the Tasmanian devil • N = 17 in the North American porcupine • N = 23 in humans • N = 25 in Graptemys (map turtles and sawbacks) • N = 37 in the American black bear • N = 134 in a butterfly

12. Mitosis • Interphase • DNA replication Lytle and Meyer Fig. 3.5 p. 37

13. Meiosis • 2N cell divides twice • Meiosis I and Meiosis II • 4 resulting cells are each 1N • Synapsis: Pairing of homologues in Prophase I • Crossing over: Exchange of chromosome tips during Prophase I • Highly variable results, genetically • Within set of four daughter cells • Each 1N cell gets one or the other of each homologous pair • Among different identical cells of a gonad that undergo meiosis • Independent assortment • Randomness of crossing over

14. Meiosis I Lytle and Meyer Fig. 3.9a p. 40

15. Synapsis and Crossing Over Lytle and Meyer Fig. 3.10 p. 43

16. Meiosis II Lytle and Meyer Fig. 3.9b p. 41

17. Asexual Reproduction • Single parent • Mitosis only • Offspring are typically clones of parent • Ex: Paramecium protozoans reproduce by mitosis for many generations • Ex: Sponge gemmules • Ex: Hydra buds • Ex: Bryozoan statoblasts Fig. 6.11 p. 125 Fig. 7.8 p. 138 Fig. 9.6 p. 180

18. Sexual Reproduction • Involves meiosis and fertilization • Meiosis: 2N cell  1N gametes • Fertilization: 1N sperm + 1N ovum  2N zygote • Genetically variable offspring • Ex: Paramecium periodically engage in sexual conjugation Fig. 5.18 p. 108

19. Parthenogenesis • Asexual mode of reproduction derived from sexual reproduction • Female’s ova develop into female offspring without fertilization • Ex: Gall midges produce sexual winged stage only when mushroom food source diminishes • Ex: Aphids feeding on leaves; a female’s granddaughters begin development in her embryonic daughters’ reproductive tracts • Ex: All-female species of whiptail lizards

20. Occasional Sex • Ex: Mesozoan parasites • Generally asexual • Switch to sexual production of gametes when crowding occurs • Ex: Some rotifers • Parthenogenic for several generations • Produce meiotic, 1N gametes • Fertilized by a sperm: 2N female (parthenogenic) • Unfertilized: 1N male, with 1N sperm HANDOUT Fig. 8.22 p. 170

21. Gender • Ovum: large, nonmotile♀ gamete, produced in an ovary • Sperm: small, motile ♂ gamete, produced in a testis • Monoecious: both gonads in the same individual • At least some species of ~½ of all animal phyla • 1) Simultaneous Hermaphrodites • Ex: Comb jellies, gastrotrichs, gnathostomulids, arrow worms (all spp. of these phyla) • Ex: Tapeworms • Ex: Earthworms • Ex: Slugs • Ex: Barnacles Fig. 8.20 p. 168 Fig. 18.16 p. 166 Fig. 11.18 p. 225

22. Gender • 2) Sequential hermaphrodites: An individual develops one type of gonad early in adulthood, then the other replaces it later • Protandry: testes first, ovaries later • Ex: Slipper shells • Ex: Clownfish • Protogyny: ovaries first, testes later • Ex: Most sequentially hermaphroditic fish

23. Gender • Dioecious: females have ovaries, males have testes • Ex: Almost all arthropods • Ex: Almost all vertebrates

24. External Fertilization • Release of gametes that meet in water is the ancestral characteristic in Animalia • Ex: Spawning palolo worms • Ex: Salmon • Ex: Frogs in amplexus Fig. 16.28 p. 345 Fig. 17.15 p. 362

25. Internal Fertilization • Sperm are delivered to ova in the female’s reproductive tract via… • …water currents (sponges) • …spermatophores • Ex: Velvet worms • Ex: Cephalopod hectocotylus • Ex: Spider pedipalp • Ex: Most salamanders Fig. 12.14 p. 241 Fig. 10.35 p. 208 Fig. 13.7 p. 251 Fig. 17.5 p. 357

26. Internal Fertilization • Sperm are delivered to ova in the female’s reproductive tract via … • …genital apposition • aka “the cloacal kiss” • Ex: Leeches and earthworms • Ex: A few frogs, toads, and salamanders • Ex: Tuatara • Ex: Most birds Fig. 11.18 p. 225 Fig. 18.23 p. 382 Fig. 19.20 p. 400

27. Internal Fertilization • Sperm are delivered to ova in the female’s reproductive tract via … • …male copulatory organ(s) • Ex: Flatworm penis • Hypodermic impregnation • Aka “penis fencing” • Ex: Shark claspers • Ex: Caecilian phallodeum • Ex: Snake and lizard hemipenes • Ex: Penis in most insects, slugs, barnacles, crocodilians, turtles, a few birds, mammals Fig. 16.6 p. 333 Fig. 18.8 p. 374

28. HANDOUT-An insect with female penis and male vagina