BIOL10004 Lecture Notes - Lecture 19: Placenta, Viviparity, Cloaca
28 Jun 2018
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MODULE 4
LECTURE 19 – REPRODUCTION
Asexual reproduction
• Mitotic cell division
• Offspring = genetically identical to parents
o No exchange of genetic materials
• Allows single individual to produce a colony
o Corals, hydra, sea star
• Common strategies among invertebrates but also some vertebrates
o Stream fish, geckos, snakes
• Can be considered as an evolutionary mechanism to extend life to find a partner
• Parthenogenesis – bees, wasps, ants
o Egg develops without being fertilised (i.e. don’t require sperm)
o Advantageous for animals living in a constant, stable environment
o Good in environment whereby it’s hard to find a mate & limited resources
§ Reproduce asexually à saves energy of finding a mate
o Can occur in vertebrates à lizards
• Facultative parthenogenesis
o Can do either sexual or asexual reproduction depending on environment, food sources and mate
availability
o Asexual = no genetic variation which is bad for the population
o Hence, usually do asexual in winter and sexual in summer
Sexual reproduction
• Exchange of genetic material
• Needs two sexes:
o Female
§ few large gametes (eggs)
§ non-motile
§ DNA and cytoplasm
o Male
§ Many small gametes (sperm)
§ Motile
§ DNA only
• Female is usually choosy about who they recombine gametes with
• Red queen hypothesis:
o Sex and recombination = necessary variation that keeps evolution going
o Without constant evolution, pathogens/competitors/environment change = extinction
Hermaphrodite – banana slug etc
• Same individual produces both sperm and eggs
• Able to self-fertilised BUT sperm & eggs usually made at diff times (prevent self-fertilisation)
• May involve sex-change
• Protandry – produces sperm when young, transform and produce eggs later
• Protogyny – eggs when young, sperm later
Budding: buds break off, begin life
independently
hydra, corals, polyps
Regeneration: differentiation of new tissues
Fragmentation
hydras, flatworms, echinoderms
Document Summary
Asexual reproduction: mitotic cell division, offspring = genetically identical to parents, no exchange of genetic materials, allows single individual to produce a colony, corals, hydra, sea star. Budding: buds break off, begin life independently hydra, corals, polyps. Sexual reproduction: exchange of genetic material, needs two sexes, female few large gametes (eggs) Dna only: female is usually choosy about who they recombine gametes with, red queen hypothesis, sex and recombination = necessary variation that keeps evolution going, without constant evolution, pathogens/competitors/environment change = extinction. External fertilisation: eggs shed by the female are fertilised by sperm in the external environment, staghorn, corals, fish, amphibians, timing of release = crucial no point releasing if there"s no sperm around. Internal fertilisation: requires important interactions environmental cues, pheromones, courtship behaviour, specialisation of external genitals compatibility to allow sperm transfer (lock & key model, usually has intromittent organ to increase efficiency of sperm transfer.
