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Definition: Diploid organisms have two copies of all chromosomes. This means they have pairs of chromosomes.
Chromosomal Count:
- Total chromosomes: 46 (23 from each parent).
- Notation: Diploid is represented as $2n$ where $n$ equals the number of chromosomes, so $2n = 46$ .

Mitosis:
- Purpose: Cell division for growth, repair, and asexual reproduction (cloning).
- Result: Two identical diploid cells, maintaining the same number of chromosomes as the original cell.
- Process: Involves doubling the genetic material, then separating it during cell division.
- Phases: Prophase, Metaphase, Anaphase, Telophase, and Cytokinesis.
- Examples: Skin cells, hair cells, and liver cells undergo mitosis.
Meiosis:
- Purpose: Sexual reproduction, producing haploid gametes (sperm and egg).
- Transformation:
  - Starting with 46 chromosomes (diploid) and reducing to 23 chromosomes (haploid).
  - Haploid is represented as $n = 23$ .
  - Important to note that haploid means 'half' the number of chromosomes.
- Process: Consists of two rounds of division, leading to four non-identical haploid gametes from one diploid cell.
- Phases: Similar to mitosis, but occurs twice with two rounds of Prophase, Metaphase, Anaphase, and Telophase.

DNA Replication: Happens in the S phase of interphase, producing double-armed chromosomes before cell division.
Chromosomal Pairing:
- After DNA replication, chromosomes appear as X-shaped structures due to the replication.
- Each pair is composed of two sister chromatids.

Introduction of Variation: Sexual reproduction through meiosis results in genetic diversity, allowing populations to adapt to environmental changes.
Siblings: They inherit half genetic material from each parent, leading to unique combinations of genetic traits, even when they may appear similar.
Importance of Genetic Variation: It enhances the population's ability to evolve and adapt over generations.

Karyotype Visualization: A karyotype is a visual representation of all the chromosomes in an organism, showing the homologous pairs.
Homologous Chromosomes:
- Definition: Chromosomes that are the same size and contain the same series of genes, though they can have different alleles.
- Example: Humans have 22 pairs of autosomal chromosomes (non-sex chromosomes) and 1 pair of sex chromosomes (XX for females, XY for males).
Sex Chromosomes:
- XX indicates a biological female.
- XY indicates a biological male.

Diploid: An organism or cell having two sets of chromosomes, typically one set from each parent (e.g., humans, 46 total chromosomes, 23 pairs).
Haploid: A cell with half the number of chromosomes; one set (e.g., gametes have 23 chromosomes).
Somatic Cells: All body cells excluding germ cells; undergo mitosis.
Germ Cells: Cells that produce gametes (sperms or eggs) through meiosis.
Gametes: Haploid cells that fuse during fertilization to form a diploid zygote.
Zygote: The initial cell formed when a sperm and egg cell merge, restoring the diploid number of chromosomes.

Gene Expression: Differences in appearance among cells from the same organism result from the expression of different genes; although they share the same genetic material, the turned-on or turned-off genes dictate their characteristics.

In Meiosis:
- DNA replication happens only once before the first division.
- Two rounds of division occur, leading to four unique haploid cells.
- Genetic material is shuffled to ensure variation in gametes.
In Mitosis:
- A single round of division is completed, resulting in two identical diploid cells.

It is crucial to understand these concepts before hands-on lab work to facilitate learning and comprehension during practical applications.