YOUTUBE: Cell division

Prokaryotes typically reproduce asexually, resulting in clones without genetic recombination.
- This process is known as binary fission.
- Steps involved in binary fission:
- DNA Replication: The chromosome of the prokaryotic cell is copied.
- Cell Division: Following DNA replication, the cell divides.
Specialized structures, known as the divisome, play a crucial role in this process.
- The ftsZ ring forms at the division site between the two cells, contributing to the formation of the septum.
The process completes when the septum has formed, resulting in two new cells.

Eukaryotes can reproduce either asexually or sexually, depending on the species.
Regardless of the mode of reproduction, eukaryotes undergo the cell cycle, which includes:
- G1 Phase: Initiates growth; the cell grows in size and synthesizes mRNA and proteins necessary for DNA synthesis.
- S Phase: DNA synthesis phase where the cell replicates its DNA, resulting in two copies of each chromosome.
- G2 Phase: Second growth phase where the cell continues to grow and prepares for division.
The stages G1, S, and G2 are collectively referred to as interphase, during which the cell prepares for division but is not yet dividing.
Mitotic Phase: The actual cell division occurs in two principal processes:
- Mitosis: Chromosomes are separated and distributed to the daughter cells.
- The nucleus must disintegrate, chromosomes separated, and a new nucleus assembled.
- Cytokinesis: The cytoplasm divides, resulting in two distinct daughter cells.
During asexual reproduction in eukaryotes, the process mirrors that of mitosis with DNA replication followed by cell division.
- Outcome: Each daughter cell is genetically identical to the parent cell.

Sexual reproduction is more complex and typically involves meiosis.
Steps in meiosis:
- Starts similarly with DNA replication.
- Divisions occur differently with the separation of homologous chromosomes instead of sister chromatids, resulting in:
- Formation of haploid cells from a diploid parent cell.
- This is followed by a second round of cell division, ultimately yielding four haploid cells.
The haploid cells can develop into:
- Gametes: Involved in fertilization with another individual, leading to genetic recombination to form a diploid individual.
- Spores: Can result from a zygote formed after sexual reproduction, allowing growth back into haploid mycelia or entering asexual reproduction.

Diatom Life Cycle:
- Mitosis occurs during the vegetative phase.
- In the sexual phase, meiosis produces gametes (egg and sperm) that fuse during syngamy, creating a genetically distinct individual.
Zygomycete Life Cycle:
- Begins with haploid filamentous hyphae forming special structures called gametangia.
- These structures fuse through plasmogamy and karyogamy to create a diploid zygote, which is short-lived.
- The zygomycete primarily exists in haploid form and undergoes meiosis to produce sporangia, which release haploid spores.
- These spores can develop into mycelia or undergo asexual reproduction through mitosis to form more haploid cells.

Prokaryotes reproduce asexually through binary fission, with potential genetic recombination via horizontal transfer.
Eukaryotes can reproduce asexually through mitosis or sexually through meiosis, leading to genetic recombination and diversity in offspring.