Bio 2.1.1

All cells come from pre-existing cells.
New cells are created through cell division.
Prokaryotic cells divide via binary fission.
Eukaryotic cells divide through mitosis and cytokinesis.
Mitosis: division of the nucleus (prophase, prometaphase, metaphase, anaphase, telophase).
Cytokinesis: division of the remaining cell contents.
Gamete production involves meiosis and cytokinesis, resulting in genetically unique nuclei.

Eukaryotic cell division is more complex due to larger amounts of DNA.
DNA replication is essential to provide a complete copy of genetic material to new cells.
Chromatin: DNA stored as chromatin, composed of DNA and proteins (histones).
Chromosomes: condensed chromatin visible during cell division; each species has a characteristic number of chromosomes (e.g., humans: $46$ ).

The cell cycle includes interphase, mitosis, and cytokinesis.
Interphase: includes G1, S, and G2 phases; DNA replication occurs during the S phase, resulting in chromosomes composed of two identical halves (sister chromatids).

Prophase: Chromosomes condense, become visible, consist of sister chromatids held at the centromeres; the spindle forms from microtubules extending from centrosomes, which move to opposite poles.
Prometaphase: Nucleolus disappears, nuclear envelope breaks down; spindle fibers attach to chromosomes, moving them to the cell's mid-region.
Metaphase: Chromosomes align along the mid-region; sister chromatids connect to opposite poles via spindle fibers.
Anaphase: Sister chromatids separate and move to opposite poles, now referred to as chromosomes; anaphase ends when chromosomes reach the poles.
Telophase: Chromosomes decondense, new nuclear envelopes form around each set of chromosomes, and spindle microtubules disappear.
Mitosis yields two genetically identical daughter nuclei.

Cytokinesis: division of cytoplasm to form two cells.
In animal cells, microfilaments constrict, dividing the cell.
Mitosis & Cytokinesis: one division of the nucleus and cytoplasm produces two genetically identical cells, each with a complete set of chromosomes.

Checkpoints ensure proper cell division.
G1 checkpoint: determines if the cell divides, enters G0 (non-dividing), or undergoes apoptosis if DNA damage cannot be repaired.
G2 checkpoint: Checks for correct DNA replication; mitosis will not proceed if errors exist.
M checkpoint: Between metaphase and anaphase, verifies chromosome attachment to the spindle for separation.

Asexual Reproduction: a single parent produces genetically identical offspring via mitosis and cytokinesis.
Sexual Reproduction: union of gametes (sex cells) to form a zygote; offspring are not identical to parents.

Homologous Chromosomes: partner chromosomes in a body cell, similar in shape, size, and centromere position; Carry information for same genetic traits.
Karyotype: display of chromosomes in a cell.
Diploid (2n): two sets of chromosomes (somatic cells).
Haploid (n): single set of chromosomes (gametes).

Prophase I: Chromatin condenses; homologous chromosomes pair up (synapsis) forming a tetrad; crossing over occurs.
Metaphase I: Tetrads align on the equator.
Anaphase I: Homologous chromosomes separate and move to opposite poles (random distribution).
Telophase I: Chromosomes decondense; nuclear envelope may reorganize; cytokinesis occurs.

Prophase II: Chromosomes appear; nuclear envelope breaks down.
Metaphase II: Chromosomes line up along the cell equator.
Anaphase II: Sister chromatids separate and move to opposite poles (now chromosomes).
Telophase II: Nuclear envelope reforms, chromosomes elongate; cytokinesis occurs.
Meiosis results in four cells, each with different genetic combinations.
Genetic recombination occurs due to crossing over in prophase I and random distribution in anaphase I.
Meiosis involves two divisions but chromosomes are only duplicated once, resulting in four haploid cells with unique gene combinations.