Asexual Reproduction

• Reproduction is the process by which an organism creates more of itself.
• Reproduction happens asexually or sexually.

Asexual Reproduction

• A single individual contributes 100% of the genetic code to its offspring.
• It leads to clones of the parent organism.
• Unicellular organisms often reproduce asexually.
• During mitosis, a yeast cell replicates all its genetic material which is followed by cytokinesis where one cell divides into two daughter cells, each with an exact copy of its DNA.
• Bacteria, yeast, and archaebacteria reproduce asexually.
• Some plants and animals also utilize asexual reproduction.
• Some bacteria share DNA through the exchange of plasmids.
• Only one organism is needed to reproduce asexually.
• Less resources and time are needed for asexual reproduction.
• Sponges reproduce by budding, where a piece of the organism pinches off and grows into a full-sized organism.
• Some plants, like citrus trees, can produce fruit with seeds without fertilization.
• Genetic diversity is sacrificed for speed.
• A single blight or virus can wipe out an entire population.
• The potato famine in Ireland occurred because potatoes, planted from pieces of other potatoes, were genetically similar and susceptible to the same diseases.
• Types of asexual reproduction include budding (sea sponges), binary fission (bacteria), sporogenesis (molds, bacteria, and fungi), fragmentation, and vegetative propagation (strawberries).
• Fragmentation is when the parent organism splits into roughly the same size "offspring."
• Vegetative propagation: strawberries shoot out runners that grow into new strawberry plants.

Sexual Reproduction

• Two individuals contribute genetic information to the offspring.
• Creates a hybrid of the two parent organisms.
• Offspring have genetic and physical traits from both parent organisms.
• Multicellular organisms use sexual reproduction.
• These organisms make sex cells (with half the DNA of the parent) combine with the sex cell of another individual, giving rise to the offspring.
• The process of making sex cells for reproduction is called meiosis.
• It allows for individuals that are a little different from the parent generation, creating a species better suited for a changing environment.
• Allows for a species to be better equipped to handle disease and changing ecological conditions.
• Mutations caused by mitosis can be passed along to offspring.
• Mutations are discarded before they reach the offspring with sexual reproduction and meiosis.
• Plants and animals both have male and female genders.
• Organisms that have both genders are hermaphrodites.
• In hermaphroditic organism reproduction, the genetic information comes together in unique combinations.
• Two sex cells from different individuals come together to form a zygote, then multiplies to create an individual.
• Fertilization is the point when the two cells share their genetic information and form the zygote.
• Fertilization happens internally (mammals) or externally (frogs, fish, and flowering plants).

Asexual Cells vs. Sex Cells

• Asexual cells are any somatic cell for a single-celled organism.
• Mitosis is the splitting of a somatic cell into two identical cells.
• These can either be new organisms or spores.
• Meiosis is the splitting of a cell with all the genetic information to two cells that have half the genetic information as the parent cell.
• A cell with half of the DNA is haploid.
• A cell with all DNA is a diploid cell.
• A somatic cell will double its genetic material before mitosis.
• A sex cell starts with two sets of DNA and goes through two sets of division to end with haploid gametes.
• Gametes are sex cells (egg for the female, sperm for the male).
• For plants, male gametes are released as pollen and carried by wind or pollinators.
• Mammals: the ovum is held in the female's body, and the male sperm is motile.
• Aquatic animals: the female lays eggs, and the male releases sperm in the water over the eggs.

Gametogenesis

• Gametogenesis is the process of making sex cells.
• In oogenesis (making eggs) and spermatogenesis (making sperm) a diploid parent cell goes through mitosis and meiosis to make up to four haploid daughter cells.
• In female humans, eggs are made in the ovaries while the fetus is still developing.
• In male humans, spermatogenesis takes place in the reproductive system and happens through the male's reproductive lifespan.
• Oogenesis starts in the pre-natal stage.
• Primary oocytes stop in the middle of meiosis I.
• In the antral stage, primary oocytes are surrounded by a follicle and a fluid-filled space called an antrum.
• The primary daughter cell retains most of the cytoplasm, and the other cell, the polar body, is much smaller.
• The polar body will eventually degenerate.
• The antral stage is triggered by puberty and the release of luteinizing hormone (LH) and follicle stimulating hormone (FSH).
• In the pre-ovulation stage, LH triggers the release of the follicle from the ovary.
• As the secondary oocyte goes through the fallopian tube, it will continue through meiosis II metaphase, where it will halt.
• Not until fertilization will it complete meiosis II and become a true ovum.
• Spermatogenesis starts the same way ova do, as undifferentiated germ cells.
• Spermatogenesis is broken into three main stages: spermatocytogenesis, spermatidogenesis, and spermiogenesis.
• Spermatocytogenesis: diploid stem cells divide into haploid spermatocytes.
• In spermatidogenesis, the secondary spermatocytes undergo meiosis II to form haploid spermatids.
• Spermiogenesis: the spermatids undergo a physiological change to become fully functional sperm cells.

Mitosis and Meiosis

• Mitosis can be classified as asexual.
• The goal of reproduction is the perpetuation of the species.
• Mitosis is a cellular division process, with diploid cells as a result.
• Most cells in the human body go through mitosis at some point.
• Meiosis is just for the purpose of reproduction.
• Meiosis will never be used for asexual reproduction.
• Each gamete will be haploid at the end.
• Sometimes, an ova will grow without being fertilized.

Asexual vs. Sexual Reproduction

Asexual Reproduction:

• A parent cell splits using mitosis to produce 2 identical daughter cells.
• Parent and daughter cells have identical, 2n or diploid DNA.
• Mitosis has prophase, metaphase, anaphase, telophase and cytokinesis.
• Mitosis can occur in any somatic cell that needs to replicate.
• Single-celled organisms use mitosis to reproduce quickly.
• Creates a population of identical individuals.
• No fertilization or incubation required.
• Occurs through budding, fission, and vegetative propagation.
• Vulnerable to changes in the environment.

Sexual Reproduction:

• An undifferentiated cell goes through meiosis to produce 4 gametes.
• Gametes are haploid, n, and have half the DNA as the parent cell.
• Meiosis has two sets of prophase, metaphase, anaphase, telophase and cytokinesis.
• Meiosis is only for the production of gametes.
• Complex organisms use meiosis .
• Creates a population of genetically diverse individuals.
• Fertilization of female gamete with male gamete to create zygote which then must incubate to maturity.
• Only meiosis makes gametes.
• Much more likely to survive drastic ecological changes.

Plant vs. Animal Reproduction

• Humans reproduce sexually.
• Females make ovum, which are then fertilized by the male sperm.
• Females incubate or gestate the zygote, then embryo, then fetus for 40 weeks.
• Most mammals, amphibians, fish, and birds reproduce sexually as well.
• Plants can generate offspring both sexually and asexually.
• Strawberries send out shoots that grow into clones of the parent plant.
• Onions, tubers like potatoes and ginger reproduce asexually.
• Most citrus trees can also reproduce asexually.
• Plants that reproduce sexually make seeds and pollen.
• Bees, butterflies, and birds aid in plant sexual reproduction by being pollinators.
• The flower of a plant houses the sexual organs of the plant, pistils and ovaries.
• The dandelion seeds are modified in a way that the lightest brush of wind can release hundreds of seeds all at once.

Asexual reproduction involves a single organism creating a copy of itself. Offspring are clones of the parent, inheriting 100% of the genetic code. Bacteria, yeast, some plants, and animals reproduce asexually through methods like mitosis and budding.