Cell Division Mitosis and Meiosis Cell Division in

Cell Division: Mitosis and Meiosis

Cell Division in Eukaryotes • Cell Cycle – The cell cycle is the repeating set of events in the life of a cell. – The cell cycle consists of cell division and interphase. – Cell division in eukaryotes includes nuclear division, called mitosis, and the division of cytoplasm, called cytokinesis.

Cell Cycle

Cell Cycle and Mitosis • Interphase – Interphase consists of growth (G 1), DNA replication, and preparation for cell division (G 2). • Mitosis is divided into stages: prophase, metaphase, and telophase. • Mitosis results in two offspring cells that are genetically identical to the original cell.

Phases of Mitosis

Phases of Mitosis • Prophase – DNA coils into chromosomes – Nuclear envelope dissolves • Metaphase – Chromosomes line up along center of cell • Anaphase – Centromeres dissolve and chromatids separate • Telophase – Nuclear envelopes reform around separated chromatids • Cytokinesis

Control of Cell Division • Cell division in eukaryotes is controlled by many proteins. • Control occurs at three main checkpoints. – G 1: Does cell need to/ is it ready to divide? – G 2: Cell mature and DNA copied successfully? – Metaphase: Chromatids paired and lined up? • Cancer may result if cells do not respond to control mechanisms

Cell Division and Cancer • Mutations of proto-oncogenes, which regulate cell growth, or tumor-suppressor genes, which prevent cell division from occurring too often, may lead to cancer. – Proto-oncogenes are like the accelerator – Tumor-suppressor genes are like the brake pedal • Cancer is the uncontrolled growth of abnormal cells.

Cell Division and Cancer

Cell Division and Cancer • Gene Expression in Cancer – Unlike normal cells, cancer cells continue to divide indefinitely, even if they become densely packed. – Cancer cells will also continue dividing even if they are no longer attached to other cells. • Causes of Cancer – A carcinogen is any substance that can induce or promote cancer. – Most carcinogens are mutagens, substances that cause mutations.

Meiosis • Meiosis is a process of nuclear division that reduces the number of chromosomes in new cells to half the number in the original cell. • Meiosis leads to four haploid cells (gametes) rather than two diploid cells as in mitosis.

Stages of Meiosis

Stages of Meiosis

Development of Gametes • Spermatogenesis is the process by which sperm cells are produced. • Oogenesis is the process that produces mature egg cells.

Meiosis in Male and Female Animals

Sexual Reproduction • Sexual reproduction is the formation of offspring through meiosis and the union of a sperm and an egg. • Offspring produced by sexual reproduction are genetically different from the parents.

When Meiosis Goes Awry • Nondisjunction: the failure of homologous chromosomes to separate during Meiosis I, or the failure of sister chromatids to separate during Meiosis II • Results in gametes with an abnormal number of chromosomes – Aneuploidy—cell having an abnormal number of chromosomes – Trisomy— 3 copies of a chromosome – Monosomy— 1 copy of a chromosome • http: //www. biostudio. com/d_%20 Meiotic%20 Nondisjunction %20 Meiosis%20 I. htm

Disorders Caused by Nondisjunction • • Trisomy 21—Down Syndrome Trisomy 13 Syndrome (Patau Syndrome) XXY—Klinefelter’s Syndrome XYY—Jacobs Syndrome XXX—Triple X Syndrome X 0—Turner’s Syndrome XXXXX syndrome

Karyotypes • A micrograph taken of an organism’s chromosomes during metaphase; arranged in homologous pairs for analysis

Trisomy 21 Karyotype