Unit 7: Animal Reproduction and Development Chapter 39

Multiples Multiple births are becoming more common – Incidence increased almost _________ in the past two decades – Fertility drugs and assisted reproduction technologies are partly responsible Multiple births concern doctors – Greater risk of : – Multiple newborns usually have lower birth weights and higher mortality rates

Modes of Reproduction 1. Sexual reproduction –Meiosis (gamete formation) followed by fertilization –Offspring ______________________ 2. Asexual reproduction –Mitosis –Single parent produces offspring –Offspring are ____________________

Asexual Reproduction Budding (example: ____________) Fission (example: _____________) Useful strategy in stable environments All offspring are clones

Cost of Sexual Reproduction Specialized cells and structures must be formed (to deliver/receive sperm) –Reproductive timing; pheromones Visual signals, special courtship, and parental behaviors can be costly Nurturing developing offspring, either in egg or body, requires resources from mother

Costs of Sexual Reproduction

Energy used to nourish offspring – _______________: thick fluid containing proteins and lipids to nourish the embryo until it can feed – Eggs with little yolk must develop larval stages quickly – Others have adequate food reserves for a more lengthy development within the shell – Some eggs have no yolk; energy must come from ______________

Developmental Processes Cell Growth Cell differentiation Morphogenesis

Stages of Development Gamete formation Fertilization Cleavage (resulting blastula) Gastrulation Organ formation Growth, tissue specialization Each stage _________________________

Development Overview Fig. 39.4, p.654

1. Gamete Formation

Sex Differences: Gamete Formation Male ____ sperm formed Sperm much small Human males produce sperm throughout life Meiosis completed during spermatogenesis Female ____ egg formed Egg larger: Why? Human females have all their eggs at birth Meiosis completed after fertilization

2. Fertilization Sperm fuses with ovum (egg) Complete when sperm nucleus fuses with egg nucleus Internal (i.e. humans, primates, dragonflies; land animals) External (i.e. fish, frogs, primarily aquatic) What are the advantages to internal vs. external fertilization?

3. Cleavage Cell division (mitosis) during early development Increase in ____________, but not volume Fig. 39.5b, p.655

Cleavage Patterns Vary Complete or incomplete (division limited to 1 part of egg) Examples of types of cleavage: Radial cleavage: _______________ Rotational cleavage: _______________

3. Cleavage Cleavage results in blastomeres (each new cell) Each species has a characteristic cleavage pattern Pattern dictates what types and proportions of materials a blastomere will get, as well as its size Fig. 39.5c, p.655

Frog Reproduction Fig. 39.5a, p.655

Maternal Instructions Sperm contributes little more than the paternal DNA The egg cytoplasm contains enzymes, RNA transcripts, microtubules, etc. These materials are not ______________ throughout the egg –________________________: certain materials are located in a particular region The egg also contains yolk, which will influence cleavage patterns

Cortex of Frog Egg gray crescent sperm penetrating frog egg yolk-rich cytoplasm pigmented cortex Fig. 39.6a, p.656

Experimental Evidence of Localized Differences Blastomeres separated after normal cleavage Blastomeres separated so one cell gets all of gray crescent Fig. 39.6b, p.656

Maternal Instructions Penetration of egg by sperm triggers a structural reorganization in the egg cytoplasm Frog egg: microtubules move granules from the animal pole to form a ____________________ Experiment done by Spemann demonstrates importance of gray crescent Near the crescent, the body axis of the frog embryo will become established and gastrulation will begin

4. Morula Produced by embryonic cleavage Rapid cell division of the zygote with virtually no growth Includes 16-cell, 32-cell, and 64-cell phases Solid ball After the 64-cell phase, develops into hollow ball, the blastula.

5. Blastula Spherical layer of cells (called ____________) Surrounding a fluid filled cavity (called ____________)

6. Gastrulation Structural reorganization Some cells move inward Produces a _____________ embryo Beginning of differentiation: ____________________ ____________________

Gastrula 3 germ layers formed: Endoderm Mesoderm Ectoderm

Late Gastrula Mesoderm Endoderm Ectoderm

Gastrulation Results in three ________ layers, or tissues: Ectoderm: _____________ – Gives rise to the nervous system and the outer layers of the integument Endoderm: _____________ – Gives rise to the gut and organs derived from it Mesoderm: ______________ – Muscle organs of circulation, reproduction, excretion, and skeleton are derived from it