Cytogenetics: Cell Cycle and Division

Vocabulary flashcards covering key terms from the cell cycle, mitosis, and meiosis as described in the lecture notes.

Cell cycle

Series of events that lead to a cell's division and DNA duplication to produce daughter cells; two parts: Interphase (growth and DNA replication) and cell division (mitosis or meiosis).

Interphase

Stage of the cell cycle where the cell grows and its DNA is replicated in preparation for division.

G1 (Gap 1)

First growth phase; the cell recovers from division and grows.

S (Synthesis)

Phase in which DNA replication occurs.

G2 (Gap 2)

Second growth/preparation phase; organelles are replicated and more growth occurs before mitosis.

Cytokinesis

Actual division of the cytoplasm resulting in two separate daughter cells.

Mitosis

Nuclear division that results in two genetically identical nuclei; typically followed by cytokinesis to form two cells.

Prophase (mitosis)

Nuclear membrane breaks down; chromosomes condense; nucleolus disappears; spindle fibers form.

Metaphase (mitosis)

Chromosomes align at the cell's equatorial plane (metaphase plate) for separation.

Anaphase (mitosis)

Centromeres split and sister chromatids are pulled toward opposite poles by spindle fibers.

Telophase (mitosis)

Nuclei reform and the cytoplasm divides (cytokinesis) to form two separate cells.

Meiosis

Nuclear division that reduces chromosome number by half; essential for sexual reproduction and genetic variation.

Diploid (2n)

Two sets of chromosomes (e.g., humans have 46 total); typical somatic cell content.

Haploid (n)

One set of chromosomes (gametes); human gametes have 23 chromosomes.

Homologous chromosomes

Pairs of chromosomes carrying the same genes at the same loci, one inherited from each parent.

Tetrad

Structure formed during prophase I when paired homologous chromosomes (each with two sister chromatids) align, consisting of four chromatids.

Chiasmata

Points where non-sister chromatids of homologous chromosomes exchange genetic material (crossing over) during meiosis.

Crossing over

Exchange of genetic material between homologous chromosomes during meiosis I, increasing genetic variation.

Synapsis

Pairing of homologous chromosomes during prophase I to form a synaptonemal complex (forming tetrads).

Leptotene

Early prophase I stage where chromosomes become visible and homologous chromosomes begin to search for each other.

Zygotene

Prophase I stage where homologous chromosomes pair (synapsis) to form bivalents.

Pachytene

Prophase I stage where synapsis is complete and crossing over can occur between homologous chromosomes.

Diplotene

Prophase I stage where homologous chromosomes separate but remain held at chiasmata.

Diakinesis

Prophase I stage where chromosomes condense further and chiasmata become apparent; tetrads are visible.

Metaphase I

Tetrads/homologous chromosome pairs move to the center of the cell for separation.

Anaphase I

Homologous chromosomes are pulled to opposite poles; sister chromatids stay together.

Telophase I

Nuclei form around each haploid set; cytokinesis may occur to form two haploid cells.

Prophase II

Spindle fibers form again in each haploid daughter cell prior to the second division.

Metaphase II

Sister chromatids align at the center of the cell (metaphase plate) in each haploid cell.

Anaphase II

Centromeres split; individual chromosomes are pulled to opposite poles.

Telophase II

Nuclei reform and the cytoplasm divides, resulting in four haploid daughter cells.

Meiosis II

Second meiotic division after meiosis I; no additional DNA replication occurs; yields four haploid gametes.

Mitosis vs Meiosis differences

Meiosis produces cells with half the chromosome number (2n to 1n), each genetically different; meiosis involves two divisions with one replication; mitosis yields identical diploid cells after one division.

Random assortment of homologous

Random orientation of paternal and maternal homologs at metaphase I, contributing to genetic variation in gametes.

Fertilization

Union of gametes that restores diploid chromosome number and creates genetic variation in offspring.

Variation

Differences among individuals in a population; meiosis and fertilization contribute to genetic diversity.