Animal Reproduction

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Animal Reproduction and Development
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Reproductive Modes
A) Asexual Reproduction

• Examples Binary Fission, Budding, Mitosis

B) Sexual Reproduction

• But, Sexual reproduction is more costly
• 1. Specialized structures for gametes
• 2. Behavioral challenges (courtship)
• 3. Investment in offspring (nourishment)
  

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Stages of Reproduction/ Development
1) Gamete Formation
MEIOSIS
Egg (n)
Sperm (n)
Gametes start out as (diploid) germ cells)
2n
2n
n
n
n
n
n
n
n
n
ovum
4 sperm cells
3 polar bodies
Males produce 4 sperm per germ cell
Females produce 1 egg per germ cell
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2) Fertilization
Zygote (2n)
Fertilization may occur

• a) Externally
• aquatic habitats
• gametes released into the environment
• large numbers of gametes produced

• b) Internally
• land-dwellers
• specialized structures for housing gametes
• embryo more protected during development

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3) Cleavage

• A cleavage furrow is formed as the egg
  dividesinto
• numerous smaller cells called blastomeres

• cleavage increases the number of cells but not
  the
• overall volume of the egg

Early cleavage (2-16 cells)
Late cleavage (more than 16 cells)
4) Blastula hollow ball of cells
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5) Gastrulation

• cellular organization, invagination

• cells become arranged into different germ layers

a) Ectoderm

• outermost layer

b) Mesoderm

• middle layer

c) Endoderm

• innermost layer

• Cell differentiation

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5) Organogenesis
6) Morphogenesis

• cell division, migration
• tissue growth, folding
• programmed cell death sculpts body parts

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Embryos may develop in several ways
A) Oviparous

• young develop outside of the mother
• feed off of egg yolk
• hatch from egg

(true egg-layers)
- Amniotic eggs have a fluid-filled sac to
protect embryo - Some eggs encased in hard outer
shell (birds)
B) Ovoviviparous

• egg contained inside female
• young feed off of yolk
• hatch from egg within uterus

C) Viviparous

• young develop inside mother
• nourished directly by mothers
• tissues (placenta)
• born live
• mammals

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Study Objectives 1. Define asexual reproduction
and give 3 examples. 2. Define sexual
reproduction. What are some costs of reproducing
sexually? 3. List the 7 stages of
reproduction/development. 4. Contrast external
and internal fertilization. In general, which
type of organisms carry out each of these
processes? 5. Define meiosis and fertilization.
Contrast sperm and egg production. 6. Define
cleavage. How does cleavage occur and what does
it accomplish? 7. Define blastomere, blastula,
and blastocoel. 8. Explain what happens during
gastrulation. 9. What are the three germ
layers? To what do these give rise in the
mature organism? 10. Define invagination.
Define differentiation. 11. Define
organogenesis. 12. Compare and contrast
oviparous, ovoviviparous, and viviparous
development.