Meiosis Oh, and a little bit of mitosis
Haploid Cells- The sex cells (egg and sperm) only contain half of the genetic diversity that diploid cells do. For humans this would mean 23 single chromosomes. The actual process of cell division is known as mitosis, this results in the production of two identical offspring cells from one original parent cell. The cell cycle which is a larger view of a cells life cycle only includes mitosis as a small part The portion of time when a cell is preparing for but not actually dividing is known as interphase. Interphase itself is broken into three subsections.
The G1 Phase is the first phase after mitosis is complete in which the newly formed daughter cells grow to a mature size. The S Phase is the middle phase of interphase, after G1 the DNA is replicated doubling its volume but causing no change in its diversity. G2 Phase This is the last phase of interphase when the cell grows and prepares for division. Mitosis then occurs and interphase may start over in both newly formed daughter cells.
G0 Phase is a phase in a cells life when it has stopped dividing or preparing for division and instead exists in a stable state carrying out its particular functions as part of a tissue. Mitosis in single celled organisms is known as binary fission and leads to the production of a new organism (one splits into two identical daughter cells. Meiosis differs from mitosis in that it produces sex cells. One diploid parent cell divides twice to form four offspring cells that have half of the genetic diversity of the parent (haploid) and are not identical
Interphase I- Genetic material is duplicated resulting in two identical chromatids bound together as chromosomes Prophase I- the longest phase, chromosomes condense as pairs then cross over (literally) with their homologous partner. This happens at numerous places and the two chromosomes swap material. Centrosomes push away from each other via nonkinetochore fibers, and the cells nucleus disperses. Kinetochore fibers bind to kinetochores and begin to pull crossed-over chromosomes toward the metaphase plate. Each chromosome pair is attached to each pole causing the PAIR to be held at the metaphase plate. Metaphase I-chromosomes are aligned on the metaphase plate but this time the centromere does not split. One chromosome of each homologous pair is attached to one centrosome.
Meiosis 1
This shows prophase 1 after crossing over has occurred. How would this increase diversity?
Anaphase I- Chromosome pairs separate from each other resulting in one chromosome from each homologous pair traveling to opposite poles (we are dividing both genetic diversity and volume in two, the result is haploid.) Telophase I and cytokinesis- Chromosomes are at opposite poles and a cleavage furrow or cell plate separate the two. Fibers break down and the cells are separated. An interphase may or may not follow. Prophase II- Any nucleus present breaks down and non-kinetochore fibers start to push centrosomes to opposite sides of the cell
Metaphase II- chromosomes line up along the metaphase plate with a kinetochore on each chromatid bound to a kinetochore fiber from each centrosome. Anaphase II- Chromatids of a chromosome replicate their centromere and are pulled to separate poles. Telophase II and cytokinesis- The chromatids move to opposite poles and a membrane forms around them to create the haploid nuclei. Cell plate or cleavage furrow forms to complete the separation.
Meiosis Definitions Synapsis- The process in which homologous chromosomes pair up with one another Tetrad- A pair of homologous chromosomes which are bound together in synapsis Crossing-over- the exchange of sections of genetic material (which carry the same characteristics) between two homologous chromosomes. Chiasmata- areas where crossed over chromosomes are actually laying across each other and get cut to be swapped
A Closer Look During Prophase
Genetic recombination- the increased genetic variation in offspring which results from crossing over and independent assortment. Why? Independent assortment (of chromosomes). Mom, and dad s chromosomes are passed along individually and randomly Gametes- This is a fancy word for sex cells..sperm and Egg in animals, Pollen and ovary in plants.
Crossing Over
Independent Assortment
Gametes
Pollen Grains
Plant Ovary
Spermatogenesis- The process of producing four healthy haploid spermatozoa from one diploid male sex cell Spermatid- snooty, means sperm Oogenesis- Process of producing one healthy haploid egg cell and three polar bodies from one diploid female sex cell. Fertilization- The act of combining two haploid sex cells (one male and one female sex cell) to create a single diploid cell which can develop into a new individual similar to its mother and father.
Oogenesis
Internal Fertilization- Fertilization that occurs when sperm is deposited inside of the female Benefits include: Drawbacks include: More developed offspring Higher survival rates Fewer chances for success A whole bunch of energy invested per baby
External Fertilization- Fertilization that occurs outside of the females body Benefits: More Babies (protection of numbers.) Less energy invested per baby. Drawbacks: Less chance of survival per baby Less developed babies
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