Cell Cycle, Mitosis, Meiosis, Karyotypes

G1 Phase (Gap 1)

Cell grows, carries out normal functions, and prepares for DNA replication.

S Phase (Synthesis)

DNA replication occurs. Each chromosome is copied, forming sister chromatids.

G2 Phase (Gap 2)

Cell continues to grow and prepares for mitosis. Proteins and enzymes needed for cell division are produced.

M Phase (Mitosis + Cytokinesis)

Division of the nucleus (mitosis) and cytoplasm (cytokinesis).

Relative Length of Each Phase

G1: Longest, S: Moderate, G2: Short, M: Very short.

Prophase

Chromatin condenses into chromosomes. Nuclear membrane breaks down. Spindle fibers form.

Metaphase

Chromosomes line up at the cell's equator. Spindle fibers attach to centromeres.

Anaphase

Sister chromatids separate and move to opposite poles.

Telophase

Nuclear membranes reform around each set of chromosomes. Chromosomes uncoil back into chromatin.

Cytokinesis

Division of cytoplasm into two daughter cells.

Products of Mitosis

2 diploid (2n) cells, genetically identical to parent cell.

Animal Cytokinesis

Cleavage furrow forms and pinches cell in two.

Plant Cytokinesis

Cell plate forms between nuclei, developing into a new cell wall.

Meiosis

Occurs in germ cells (cells that produce gametes). Produces haploid (n) gametes.

Prophase I

Chromosomes condense. Synapsis: homologous chromosomes pair up. Crossing over occurs.

Metaphase I

Homologous pairs line up at the equator. Independent assortment occurs.

Anaphase I

Homologous chromosomes separate to opposite poles.

Telophase I and Cytokinesis

Two haploid cells form (chromosomes still duplicated).

Products of Meiosis

4 haploid (n) cells, genetically unique due to crossing over and independent assortment.

Karyotypes

Display of all chromosomes in a cell arranged by size and shape.

Sex Chromosomes

Determine biological sex. XX = female, XY = male.

Monosomy

Missing one chromosome (e.g., Turner syndrome, XO).

Trisomy

Extra chromosome (e.g., Down syndrome, Trisomy 21).

Haploid (n)

Cell with one set of chromosomes (gametes).

Diploid (2n)

Cell with two sets of chromosomes (somatic cells).

Crossing Over

Exchange of genetic material between homologous chromosomes during Prophase I.

Synapsis

Pairing of homologous chromosomes during Prophase I.

Gamete

Sex cell (sperm or egg).

Zygote

Fertilized egg formed from fusion of gametes.

Somatic Cell

Body cell that undergoes mitosis.

Chromatin

Uncoiled DNA and proteins in the nucleus.

Chromatid

One half of a duplicated chromosome.

Chromosome

Condensed DNA molecule containing genetic information.

Mitosis vs. Meiosis

Mitosis: Somatic (body) cells, 1 division, 2 daughter cells, diploid. Meiosis: Germ cells, 2 divisions, 4 daughter cells, haploid.