Cellular Reproduction Mitosis & Meiosis

Chromosome Structure Chromatin – Thin, uncoiled strands of DNA & proteins (histones) Chromosomes – Rod-shaped structures composed of coiled strands of DNA & proteins. Chromosomes are made up of two sister chromatids held together at a central point called a centromere.

Chromosomes

The Cell Cycle G1 Period – Cell growth S Period – DNA Replication G2 Period – Rapid cell growth Mitosis – Cell division Cytokinesis – Cytoplasmic division

The Cell Cycle

Interphase Comprised of the G1, S, & G2 periods. A period of preparation for mitosis.

The Phases of Mitosis Period of nuclear division Prophase Metaphase Anaphase Telophase

Prophase Chromatin coils to form chromosomes. Nucleolus & nuclear membrane disappear. Spindle fibers begin to develop. Kinetochore fibers (pole to chromosomes); Polar fibers (pole to pole) Formation of asters. Asters: Protein fibers that radiate from each pole.

Metaphase Chromosomes move to the equator/center of the cell. Metaphase plate formation

Anaphase Centromeres of each pair of chromatids divide. Chromatids separate & move to opposite poles.

Telophase Centrioles & spindle fibers disappear Chromatids unwind to form chromatin Nuclear membrane & nucleolus reappear

Cytokinesis The division of the cytoplasm ANIMAL CELL – cleavage furrow PLANT CELL – cell plate formation Cell Plate

Phases of Mitosis

Meiosis Process of nuclear division that reduces chromosome number in half. Used to create germ cells (gametes) Two divisions Meiosis I Meiosis II

Meiosis I Prophase I Nuclear membrane/nucleolus disappear Crossing Over Prophase I Nuclear membrane/nucleolus disappear Chromosomes form from chromatin Homologous chromosomes line up together in process called synapsis (form tetrads) Crossing over occurs (Genetic Recombination) Spindle fibers form. Metaphase I Homologous chromosomes move to equator. Anaphase I Homologous chromosomes separate & move to poles. Telophase I Cytoplasm divides (forms 2 daughter cells) Nuclear membrane & nucleolus reappear

MeiosisII Most like Mitosis Prophase II Metaphase II Anaphase II Click** Most like Mitosis Prophase II Nuclear Membrane & nucleolus disappear Metaphase II Chromosomes line up on equator Anaphase II Chromatids separate Telophase II Nuclear membrane & nucleolus reappear Chromosomes uncoil

Karyotype

Formation of Gametes – Result of Meiosis Spermatogenesis Occurs in males. Four sperm cells are formed. Oogenesis Occurs in females. I egg (ovum) formed. 3 polar bodies formed, but eventually disintegrate.

Chromosome Numbers Chromosomes appear in pairs in all sexually reproducing organisms. Called homologous chromosomes Same shape & same size Diploid number (2N) – A cell containing both chromosomes of a homologous pair. Haploid number (1N) – A cell containing one chromosome of a homologous pair.

Diploid vs. Haploid Cells

Mitosis Production vs Meiosis Somatic cells are body cells Formed via ________________ Somatic cells are (diploid/haploid) Germ cells are reproductive/sex cells (gametes) Germ cells are (diploid/haploid)

Mitosis vs. Meiosis