Human Reproduction

propagation of the species, so that generations after generations can be in existence

• asexual and sexual
• both
• both, one or none

• propagation of a new offspring by mitosis; one parent (monotonous reproduction
• Result: produces a genetically identical copy of itself, a clone; no genetic variation

• budding
• fission
• gemmules
• fragmentation
• parthenogenesis

• budding: outgrowths of existing individuals; a group of cells grow on the body and, through mitosis, grows to become a new individual, which then detaches
• ex: invertebrates

separation individuals of approximately the same size.

specialized diploid cells are partitioned (set aside) somewhere in the parent--> released into the environment--> divide mitotically to form a new individual

• breaking into pieces, where each piece regenerates its missing part by regeneration
• Example: earthworm

• a new haploid individual forms from an unfertilized egg
• Individuals are sterile; some remain haploid; others turn diploid
• Example: bees [worker]

• not finding mate; if species is scarce, they don't worry
• more offspring at a faster rate
• if the gene pool is favorable, it passes on, assuring persistence

• If there is a bad gene, it is transferred
• lack of diversity
• unfavorable genes perpetuate (deleterious)

• two parents each produce haploid gametes, fuse in fertilization, and form a diploid zygote
• - creation of an offspring by fusion of a male gamete (sperm) and female gamete (egg) to form a zygote

• meiosis
• mitosis

• genetic variation via recombination and independent assortment
• - every offspring can be genetically differetn from every other offspring
• - recombination does a good job hiding deleterious genes (recessive genes)
• Changing environments are accommodated through adaptations

• finding a mate
• takes a longer time

• individuals contain both male and female gonads and other reproductive structures
• They reproduce sexually, but do not self-fertilize [eggs can be fertilized by own sperm]
• Example: earthworm and sea slugs (sea slugs produce own sperm and eggs; in a few weeks, new individuals hatch from fertilized eggs)

• sex reversal
• female can change into a male and vice versa via environmental cues

• critical timing
• mediated by environmental cues (pheromones and chemical attractants (maybe))
• courtship and mating behaviors

external and internal

• 1) union of gametes outside body:- male and female release gametes into environment; has to be moist environment
• 2) accompanied by large #s of gametes being spread to ensure some gametes will be successful in finding other gametes: - the further the distance away the male is from the female, the more eggs the female sheds (only females; sperm is always in large #s)
• 3) Attraction to eggs: - pheromones and chemical attractants

• pheromones: hormones that are released that help lure/ affect behavior of opposite sex
• chemical attractants: materials released by the outer coats of eggs/ some are highly specias specific/ characteristic of external because internal isn't as important

important for proper union

• 1) The sperm are deposited inside female--> gametes fuse inside body
• 2) Requires some behavioral interactions- a copulatory organ--> male needs some way to place sperm inside body

• development can be outside or inside body
• There are three types of organisms depending on whether development is inside or outside the body.

• oviparous
• viviparous
• ovoviviparous

• 1) egg-laying animals
• 2) little/ no development occurs in mom
• 3) before egg is shed, its covered with protective casing (may be hard shell or leathery)
• Examples: most fish, amphibians, and reptiles; all birds; most insects; etc.

• 1) internal fertilization and internal development where the embryo and the mom are connected by a placenta formed between the mom and baby
• 2) Mom's blood vessels in close proximity to th ebaby's blood vessels, enabling nourishing of the baby, waste being taken away, etc. by the placenta
• Examples: all placental mammals, except marsupials.

•  1) internal fertilization, but the embryos are carried in body, either the male or female body
• 2) no interaction between the parent body and embryo
• 3) embryo grows in self-sufficient manner, not relying on parent for anything but a place during its growth
• 4) appears as live birth because the casing breaks open and allows release of offspring
• Examples: marsupials and frogs

• 1) most animals exhibit reproductive cycles related to changing seasons
• 2) Reproductive cycles are controlled by hormones and environmental cues.
• 3) Estrous vs. Menstrual

• Occurs in most female placental mammals, except humans.
• It is often referred to as "heat" where the female is reproductively receptive to the male; corresponds to ovulation cycle in female where she is receptive to intercourse with the male
• Humans and males are exceptions

• gonads (gametes/ sex hormones)
• accessory structures (ducts/ glands)
• external genitalia

gonads

play role in nourishment, transport, protection of fertilized egg and developing embryo

necessary for union of male and female