Chromosomes and Cell Reproduction The Cell Cycle The

Chromosomes and Cell Reproduction

The Cell Cycle The cell cycle is a repeating sequence of cellular growth and division during the life of an organism. A cell spends 90 percent of its time in the first three phases of the cycle.

G 0 PHASE DNA SYNTHESIS CELL GROWTH & PREP. FOR MITOSIS M PASE

A cell will enter the last two phases of the cell cycle only if it is about to divide. key checkpoints at which feedback signals from the cell can trigger the next phase of the cell cycle (green light). Overview of the cell cycle Cell Cycle Movie/ Game

Bacterial cells divide to reproduce Binary fission is a form of asexual reproduction that produces identical offspring: Mitosis

Chromosome Structure Chromosomes are the coiled up version of DNA. They consist of DNA and proteins: histones and nonhistones How Chromosomes Coil

Each half of a chromosome is an exact copy called a chromatid.

Chromatids are attached at the center called a centromere.

A gene is a segment of DNA that codes for a protein or RNA molecule.

Cell Types Somatic Cells Gametes

Chromosome Numbers Types: Autosomes and Sex Chromosomes (XX or XY). Humans: 22 pair of homologous chromosomes and 1 pair of sex chromosomes.

Chromosome Numbers All of the cells in the body, other than gametes are Diploid (2 n=46 in humans). Gametes contain only one set of chromosomes: Haploid (n=23 in humans).

Different species have different numbers of chromosomes.

Change in chromosome number Humans who are missing even one of the 46 chromosomes usually do not survive. Humans with more than two copies of a chromosome, result in a condition called trisomy.

Abnormalities in chromosome number can be detected by analyzing a karyotype. Nondisjunction during the production of gametes results in gametes having more or less chromosomes than normal. Pictures called karyotypes can detect problems after conception. Karyotypes Explained

When control is lost: cancer Cancer is the uncontrolled growth of cells. Mutations in genes that control cell division may result in cancer. Cancer Biology All the Details

The Phases of Mitosis Interphase Prophase Metaphase Anaphase Telophase The Jazzy Version of Mitosis MITOSIS Cytokinesis I Prefer My Awesome Teacher…Cool!

Prophase 1. Chromosomes coil and become visible. CENTRIOLES MITOTIC SPINDLE NUCLEAR ENVELOPE 2. Nuclear envelope & nucleolus breaks down. 3. Mitotic Spindle fibers begin to form. CENTROMERE HOMOLOGUES

Metaphase 1. Chromosomes line up along the equator of the cell. 2. Spindle fibers attach to kinetochore. 3. Centrioles migrate to the poles of the cell.

Anaphase 1. Spindle fibers begin to shorten. 2. Chromatids separate. 3. Chromatids begin moving toward the poles of the cell.

1. Nuclear envelope reforms. 2. Cleavage furrow forms pinching the cytoplasm. 3. Chromosomes uncoil. 4. Cytokinesis begins. Telophase

Cytokinesis During telophase, cytokinesis occurs. During cytokinesis, the cytoplasm of the cell is divided in half, and the cell membrane grows to enclose each cell.

Cleavage In Action

Meiosis USA 300, 000 strong and growing Meiosis produces gametes and reduces the number in chromosomes in half. The following presents mitosis on the left and the corresponding meiosis phase on the right…. notice the differences. First Link First

Prophase I GENTEIC RECOMBINATION INDEPENDENT ASSORTMENT SYNAPSIS

Metaphase I

Anaphase I

Telophase & Cytokinesis Telophase I & Cytokinesis I

None Prophase II

None Metaphase II

None Anaphase II

None Telophase II & Cytokinesis II

Formation of Gametes Spermatogenesis spermatids

Oogenesis OVUM Third Link Comparison of OOGENESIS & SPERMATOGENISIS

So How Do Mitosis and Meiosis Compare? . Comparison of Mitosis and Meiosis

Types of Reproduction Sexual and Asexual