Animal Reproduction Flashcards

Asexual Reproduction

• Produces genetically identical clones.
• No need to find a mate.
• Can produce large numbers of offspring quickly.
• Includes fission, budding, fragmentation, and parthenogenesis.

Fission

• Binary fission divides an organism in two.
• Occurs after a period of growth.
• Examples: Some bacteria and single-celled eukaryotes like amoebas.

Budding

• A smaller organism emerges from the parent.
• Examples: Hydras, corals, yeast.

Fragmentation

• Generates new flatworms.

Parthenogenesis

• Reproduction without male fertilization.
• Egg develops without fertilization.
• Occurs in invertebrates like bees and wasps, and vertebrates like some reptiles, amphibians, and fish.
• Example: Cnemidophorus lizards.

Disadvantages of Asexual Reproduction

• Lack of genetic diversity.
• May be problematic if environmental conditions change.
• Homogenous populations may struggle with changing conditions.
• Example: Amazon molly.

Sexual Reproduction

• Involves the exchange of genetic material.
• Requires searching for a mate.
• Increases genetic diversity.
• Offspring potentially more resilient to changing environments.

Gametes

• Genetic material is delivered by gametes.
• Gonads produce gametes through meiosis.
• Gametes are sperm/eggs.
• In vertebrates, sperm or egg production occurs in one animal based on sex determination.
• Hermaphrodites produce both gamete types; common in invertebrates like earthworms, flatworms, snails, etc.

Gametogenesis and Fertilization

Gametogenesis

• Produces gametes.
  • Spermatogenesis: produces sperm.
  • Oogenesis: produces eggs.
• Eggs are usually much larger than sperm.
  • Require more energy to produce.
  • Have greater value.
  • Females often have mate choice.

Fertilization

• Joins sperm and egg.
• Produces the diploid zygote.
  • Joins haploid sperm and egg.
• Occurs externally or internally.
• One sperm cell needs to fertilize one egg, and the species needs to match up

External Fertilization

• Typically occurs in aquatic environments.
• Common in sea urchins, corals, and fish.
• Sperm have to find the egg of the appropriate species.
• Sea urchins release billions of sperm that locate the egg by swimming towards chemical signals released by the egg.

Internal Fertilization

• Occurs in mammals.
• Sperm delivered to the vagina where they swim towards the egg.
• Aided by chemical and mechanical signals.
• In human ejaculate, 200-300 million sperm, but only ~200 get near egg.
• Only one sperm cell fertilizes the egg.

Sexual Selection

• Female gamete is larger and more energetically expensive to produce.
• Leads to female mate choice in many species.
• Females are less likely to mate with males of low quality.
• Males must then prove themselves.
• Males produce showy displays to prove their quality; to attract females, increasing mating success.
• Potential negative consequences.