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Reproduction. Asexual vs. Sexual. Asexual Reproduction. Asexual reproduction is the formation of new individuals from the cells of a single parent. It is very common in plants; less so in animals.
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Reproduction Asexual vs. Sexual
Asexual Reproduction • Asexual reproduction is the formation of new individuals from the cells of a single parent. It is very common in plants; less so in animals. • Or in the case of cells, asexual reproduction is making a new cell that is the same as the parent cell.
Asexual Reproduction in Plants—Stems!!! • All plant organs have been used for asexual reproduction, but stems are the most common. • In some species, stems arch over and take root at their tips, forming new plants. • The horizontal above-ground stems of the strawberry produce new daughter plants.
Asexual Reproduction in Plants—Leaves!! • This photo shows the leaves of the plant Bryophyllum. Mitosis along the leaf margins produces tiny plantlets that fall off and form new plants.
Asexual Reproduction in Plants—Roots! • Some plants use their roots for asexual reproduction. • The dandelion is a common example. • Trees, such as the poplar or aspen, send up new stems from their roots. In time, an entire grove of trees may form — all part of a clone of the original tree.
Asexual Reproduction in Plants—Plant propagation by people • Commercially-important plants are often deliberately propagated by asexual means in order to keep particularly desirable traits (e.g., flower color, flavor, resistance to disease). • Cuttings may be taken from the parent and rooted. • Grafting is widely used to propagate a desired variety of shrub or tree. All apple varieties, for example, are propagated this way.
Asexual Reproduction in Animals--Budding • In budding, offspring develop as a growth on the body of the parent. • In some species, e.g., jellyfishes and many echinoderms, the buds break away and take up an independent existence. • In others, like corals, the buds remain attached to the parent and the process results in colonies of animals. • Budding is also common among parasitic animals, e.g., tapeworms.
Asexual Reproduction in Animals--Parthenogenesis • In parthenogenesis ("virgin birth"), the females produce eggs, but these develop into young without ever being fertilized. • Parthenogenesis occurs in some fishes, several kinds of insects, and a few species of frogs and lizards.
So why don’t all organisms reproduce asexually? • You don’t have to waste all that time finding a mate. And you get to pass on all of your own genes!!!
The advantages of Sexual reproduction • Sexual reproduction allows for greater diversity. • “Bad genes” can get covered up by good ones from the other parent. • Combinations of genes make it so organisms can better deal with changing environments.
So, now for cells and asexual reproduction. • The cell cycle asexually produces new body cells for: • Repair • Replacement • Growth
The Cell Cycle • The cell cycle consists of three main parts. • Interphase • Mitosis • Cytokinesis
Interphase • During interphase, the cell is preparing to divide by making more organelles and copying its DNA.
Mitosis • Mitosis is when the cell is actually making the new cells. It consists of 4 steps or phases. • Prophase • Metaphase • Anaphase • Telophase
Prophase • During prophase, the chromatin condenses into chromosomes.
Metaphase • During metaphase, chromosomes line up in the middle of the cell
Anaphase • Anaphase is when the chromosomes move to the opposite ends.
Telophase • In telophase, the chromosomes reach the opposite ends and the cell gets ready to actually split.
Cytokinesis • During cytokinesis, the cell divides into two cells.
Results of Mitosis • Produces new body cells • Cell copies DNA once • Cell splits once • 2 new (daughter) cells • Daughter cells the same as the parent cells • Daughter cells have the same number of chromosomes as the parent cells
Cells and Sexual Reproduction • A different type of cells must be produced for sexual reproduction. • These different cell are called sex cells, or gametes • Egg = female gamete • Sperm = male gamete
Gametes!!! • Since the gametes are going to unite to make a new organism, each gamete only needs to have half the genetic information as its parent cell. • In mitosis, the cell copied its DNA once and split once. • In making sex cells, the cell has to copy it’s DNA once and then split twice.
Meiosis • The process of making gametes by copying the DNA once, and splitting twice is called meiosis.
Results of Meiosis • Produces gametes (Sex cells) • Cell copies DNA once • Cell splits twice • 4 new (daughter) cells • Daughter cells different from parent cells • Daughter cells have the half the number of chromosomes as the parent cells
Cell Division Comparison Mitosis Meiosis • Produces body cells • Cell copies DNA once • Cell splits once • 2 new (daughter) cells • New cells the same as the parent cells • Daughter cells have the same number of chromosomes as the parent cells • Produces gametes • Cell copies DNA once • Cell splits twice • 4 new (daughter) cells • New cells different from parent cells • Daughter cells have the half the number of chromosomes as the parent cells
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