BIOL 125 – BIOLOGY I Study Guide – Ch. 10 – Chromosomes, Mitosis, and Meiosis

DNA: Deoxyribonucleic acid, the molecule that carries the genetic instructions for life.
Gene: A segment of DNA that encodes a functional product, typically a protein.
Chromosome: A structure composed of DNA and protein that carries genetic information; humans have 46 chromosomes in somatic cells.
Chromatin: The complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells, existing in a less condensed form during interphase.
Histone: A family of basic proteins that associate with DNA in the nucleus to form chromatin.
Nucleosome: The structural unit of chromatin, consisting of a segment of DNA wound around a core of histone proteins.
Histone H1: A linker histone that helps in the compaction of chromatin, anchoring the nucleosome to the DNA.
Scaffolding Protein: Proteins that help organize the DNA and contribute to chromatin structure.
Condensin: A protein complex that plays a key role in the condensation of chromosomes during mitosis and meiosis.

Cell Cycle: The series of events that take place in a cell leading to its division and duplication.
Interphase: The phase of the cell cycle where the cell spends most of its life; includes G1, S, and G2 phases.
- G1 Phase (Gap 1): Cell grows and performs normal functions; checks for cell size, nutrients, and DNA integrity.
- S Phase (Synthesis): DNA replication occurs, resulting in duplicated chromosomes (sister chromatids).
- G2 Phase (Gap 2): Further cell growth; preparation for mitosis; checks for errors in DNA replication.
M Phase (Mitosis): The phase where the cell divides its copied DNA and cytoplasm to form two new cells.

Mitosis: The process of nuclear division where each daughter cell receives an identical set of chromosomes.
Cytokinesis: The division of the cytoplasm, occurring after mitosis, resulting in two separate daughter cells.

Prophase: Chromosomes become visible, centrioles move to opposite poles, and the mitotic spindle begins to form.
Prometaphase: Nuclear envelope breaks down, spindle fibers attach to kinetochores of chromosomes.
Metaphase: Chromosomes align at the cell's equatorial plane or metaphase plate.
Anaphase: Sister chromatids are pulled apart toward opposite poles of the cell.
Telophase: Chromatids reach the poles, nuclear envelopes reform, and chromosomes begin to de-condense.
- Cytokinesis (after Telophase): Animal cells form a cleavage furrow; plant cells form a cell plate.

Asexual Reproduction: Produces clones via mitotic division, resulting in offspring genetically identical to the parent.
Sexual Reproduction: Involves the fusion of gametes, resulting in genetic variability; produces a zygote.
- Gamete: A haploid reproductive cell (sperm or egg).
- Zygote: The diploid cell resulting from the fusion of two haploid gametes.
Homologous Chromosomes: Chromosomes that have the same sequence of genes and structure but may have different alleles.
- Diploid (2n): A cell that contains two complete sets of chromosomes, one from each parent.
- Haploid (n): A cell with a single set of chromosomes, characteristic of gametes.
- Polyploidy: A condition where a cell has more than two paired (homologous) sets of chromosomes.

Meiosis: A specialized form of cell division that reduces the chromosome number by half, resulting in four haploid cells.
Prophase I: Chromosomes condense; homologous chromosomes undergo synapsis to form tetrads; crossing-over occurs at chiasmata.
Metaphase I: Tetrads align at the metaphase plate; spindle fibers attach.
Anaphase I: Homologous chromosomes are separated and pulled toward opposite poles.
Telophase I: Chromosomal distribution to daughter cells; may be followed by interkinesis.
- Interkinesis: A short resting phase that occurs between meiosis I and meiosis II, where no DNA replication takes place.
Prophase II: Chromosomes condense again if they had de-condensed.
Metaphase II: Chromosomes align individually at the metaphase plate.
Anaphase II: Sister chromatids are pulled apart to opposite poles.
Telophase II: Nuclear envelopes reform; results in a total of four haploid daughter cells.

Ways Meiosis Generates Genetic Diversity:
1. Crossing-over: The exchange of genetic material between homologous chromosomes during prophase I, resulting in recombination of genetic information.
2. Independent Assortment: The random assortment of maternal and paternal chromosomes during metaphase I, leading to a variety of combinations in the gametes.

Meiosis: Results in four genetically diverse haploid cells; includes two rounds of division and involves crossing-over.
Mitosis: Results in two genetically identical diploid cells; one round of division only.
Differentiation of Phases:
- Metaphase I vs. Mitotic Metaphase: In metaphase I, tetrads align whereas in mitosis, individual chromosomes align.
- Anaphase I vs. Mitotic Anaphase: In anaphase I, homologous chromosomes are separated; in mitotic anaphase, sister chromatids are separated.
- Telophase I vs. Mitotic Telophase: Telophase I results in two cells with half the number of chromosomes, while mitotic telophase results in two cells with the same number of chromosomes as the original cell.
- Metaphase II vs. Metaphase I: In metaphase II, sister chromatids align individually; in metaphase I, homologous chromosomes align as tetrads, impacting genetic variability in daughter cells.