Mitosis Produces two identical daughter cells

Mitosis • Produces two identical daughter cells. • Each daughter cell has the same kind and number of chromosomes as the original parent cell.

The Stages of Mitosis § Prophase § The cell’s chromatin tightens. § The chromosome consist of two sister chromatids, which are attached at the centromere. § Two centrioles move to opposite poles of cell, and start to form spindle fibers (consist of microtubules).

Cellular Reproduction § The nuclear envelope seems to disappear. § Spindle fibers attach to the sister chromatids at the kinetochore (region in centromere).

Prophase Animal cell Plant cell

Cellular Reproduction Metaphase § Sister chromatids are pulled along the spindle apparatus toward the center of the cell. § They line up in the middle of the cell. (equatorial plate)

Metaphase Animal cell Plant cell

Cellular Reproduction Anaphase § The microtubules of the spindle apparatus begin to shorten. § The sister chromatids separate. § The chromosomes move toward the poles of the cell.

Anaphase Animal cell Plant cell

Cellular Reproduction Telophase § The chromosomes arrive at the poles and begin to relax. § Two new nuclear membranes begin to form and the nucleoli reappear. § The spindle apparatus disassembles.

Telophase Animal cell Plant cell

Cellular Reproduction Cytokinesis § In animal cells, microfilaments constrict, or pinch, the cytoplasm. § In plant cells, a new structure, called a cell plate, forms.

MEIOSIS

Meiosis § The sexual life cycle in animals involves meiosis. § Meiosis produces gametes in which the number of chromosomes is reduced by half. § When gametes combine in fertilization, the number of chromosomes is restored.

Stages of Meiosis § Involves two consecutive cell divisions called meiosis I and meiosis II Meiosis I § Interphase § Chromosomes replicate. § Chromatin condenses. Interphase

Meiosis I § Prophase I § Pairing of homologous chromosomes occurs. § Each chromosome consists of two chromatids. § The nuclear envelope breaks down. § Spindles form. Prophase I

Meiosis I § Metaphase I § Chromosome centromeres attach Metaphase I to spindle fibers. § Homologous chromosomes line up at the equator.

Meiosis I § Anaphase I § Homologous chromosomes separate and move to opposite poles of the cell. Anaphase I

Meiosis I § Telophase I § The spindles break down. § Chromosomes form two nuclei. § The cell divides. Telophase I

Meiosis II § Prophase II § A second set of Prophase II phases begins as the spindle apparatus forms and the chromosomes condense.

Meiosis II § Metaphase II § A haploid number of chromosomes line up at the equator. Metaphase II

Meiosis II § Anaphase II § The sister Anaphase II chromatids are pulled apart at the centromere by spindle fibers and move toward the opposite poles of the cell.

Meiosis II § Telophase II § The chromosomes Telophase II reach the poles, and the nuclear membrane and nuclei reform.

Meiosis II § Cytokinesis results in four haploid cells, each with n number of chromosomes. Cytokinesis

The Importance of Meiosis § Meiosis consists of two sets of divisions § Produces four haploid daughter cells that are not identical § Results in genetic variation