Embryology Winter 2011

1. EmbryologyWinter 2011

2. Sexual Vs. Asexual Reproduction • The creation of new individuals from existing ones is called reproduction • Two types of reproduction: • Asexual (reproduction without sex) • Sexual

3. Asexual Reproduction • Three types of asexual reproduction • 1) Budding • 2) Fission • 3) Fragmentation • Budding – • Splitting off new individuals from existing ones • Seen in many invertebrates (i.e. – hydra)

4. Asexual Reproduction - Fission • Fission – • The separation of a parent into two or more individuals of equal size

5. Asexual Reproduction – Fragmentation • Fragmentation – • The breaking of the parent into several pieces, some or all of which develop into complete adults • Must be accompanied by regeneration the re-growth of lost body parts • An entirely new individual can develop from a fragmented part (i.e. – star fish)

6. Asexual Reproduction – Advantages & Disadvantages • Advantages- • Organisms who live in isolation can reproduce • Organisms can reproduce many offspring quickly • Disadvantages – • No genetic variation • If the environment changes, the entire population may die out

7. Sexual Reproduction • Sexual Reproduction – the creation of offspring by the fusion of two haploid sex cells (gametes)  forms a diploidzygote(fertilized egg) • Gametes: • Sperm – moves via flagellum, small cell • Egg – not mobile, large cell

8. Alternative Reproduction • Some organisms can reproduce via both asexual and sexual reproduction • i.e. – rotifer • Hermaphrodite – an individual with both female and male reproductive organs • Can fertilize their own eggs (tapeworms) • Usually reproduce with another hermaphroditic organism (earthworms)

9. Fertilization Methods • External fertilization – • Parents “discharge” their gametes into the water  fertilization occurs here • Often, male and female never even touch • i.e. - most fish, amphibians • Internal fertilization – • When sperm are deposited in or close to the female reproductive tract • i.e. – females & males