What is the function of the reproductive system?
propagation of the species, so that generations after generations can be in existence
Types of reproduction:
Which occur in animals?
Which one is used?
- asexual and sexual
- both, one or none
Asexual reproduction: __
- propagation of a new offspring by mitosis; one parent (monotonous reproduction
- Result: produces a genetically identical copy of itself, a clone; no genetic variation
What are the kinds of asexual reproduction?
- 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]
Advantages of asexual reproduction.
- 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
Disadvantages of asexual reproduction.
- If there is a bad gene, it is transferred
- lack of diversity
- unfavorable genes perpetuate (deleterious)
What is sexual reproduction?
- 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
Gametes form by __--> fertilization--> zygote--> grows by __.
Advantages of sexual reproducion?
- 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
Disadvantages of sexual reproduction.
- 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)
Some species undergo __. Explain it.
- sex reversal
- female can change into a male and vice versa via environmental cues
What does all fertilization require?
- critical timing
- mediated by environmental cues (pheromones and chemical attractants (maybe))
- courtship and mating behaviors
What are the two types of fertilization in sexual reproduction?
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
What are phermones 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
Why are courtship behavior and mating behaviors 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
What is special about internal fertilization?
- development can be outside or inside body
- There are three types of organisms depending on whether development is inside or outside the body.
Internal fertilization and the modes of development.
- 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
Explain reproductive cycles.
- 1) most animals exhibit reproductive cycles related to changing seasons
- 2) Reproductive cycles are controlled by hormones and environmental cues.
- 3) Estrous vs. Menstrual
Explain the estrous reproductive cycle.
- 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
Any organism that reproduces sexually must have:
- gonads (gametes/ sex hormones)
- accessory structures (ducts/ glands)
- external genitalia
pair of primary reproductive organs
play role in nourishment, transport, protection of fertilized egg and developing embryo
necessary for union of male and female