Mitosis and Asexual Reproduction

Cell Cycle Mitosis Cytokinesis Period of time from one division to the next Unicellular division results in formation of new individuals of the species Cell Cycle Multicellular division results in replacement of old or damaged cells Process by which the nucleus divides while maintaining number of chromosomes Mitosis Cytokinesis Division of the cytoplasm Asexual Reproduction Reproduction that only involves one parent so therefore no special reproductive organs are needed

Interphase Prophase Metaphase Anaphase Telophase Nuclear DNA wound around proteins known as histones Chromatin Chromosomes Condensed rolls of chromatin that are able to be seen during mitosis (rod-like structures) There are 5 phases in MITOSIS Interphase Prophase Metaphase Anaphase Telophase

Draw Interphase Interphase Known as “resting phase” Cells grow in size by producing more nucleic acids, proteins, and cellular organelles Chromosomes make copies of themselves, but they can’t be seen Nucleus of the cell is contained within the nuclear envelope Centrioles are present and duplicate themselves Draw Interphase

Draw a Chromosome One Double Chromosome Prophase Double chromosomes become visible - Chromatid Chromosomes are 2 sister chromatids connected by a centromere Draw a Chromosome Centromere Sister Chromatids One Double Chromosome

Draw Prophase DON’T DRAW At the beginning, centrioles move to opposite poles Aster (star shaped fibers) extend = microtubules Spindle fibers attach (to centromere to pull away chromatids to opposite sides of the cell) By the end, the nuclear envelope and nucleus have disappeared Draw Prophase EARLY LATE DON’T DRAW

Draw Metaphase Metaphase Centromeres line up on the equator (middle= metaphase plate) By the end, the centromeres divide and pull the daughter chromosomes to opposite sides of the cell Half of each chromosome goes to the opposite side of the cell Draw Metaphase

Draw Anaphase Anaphase Daughter chromosomes move to opposite sides of cell (poles) Movement is accomplished by the microtubules Movement occurs by shortening of the microtubules Draw Anaphase

Draw Telophase Telophase Chromosomes uncoil and return to previous shape (threadlike) Nuclear membrane and nuclei reform Draw Telophase NOTE: Cytokinesis begins during late anaphase and finishes during telophase

Mitosis in Plants Same as mitosis in animals except: Plants have no centrioles – spindle fibers take their place Asters do not form Cell wall does not pinch because it is too rigid Cell plate divides the cell into two

Asexual Reproduction Occurs only through the process of mitosis Each offspring has the same genetic information Where can asexual reproduction be found? BACTERIA YEAST PLANTS

Meiosis Sexual Reproduction

SEXUAL REPRODUCTION Sex cells formed by meiosis Requires 2 parents Offspring not identical Meiosis The process that results in the formation of gametes Gametes Sex cells, egg or sperm, which have haploid chromosomes Haploid Haploid means HALF, as in the number of chromosomes, written as n

The union of an egg and a sperm Fertilization n 2n The union of an egg and a sperm Zygote The cell that is formed when the egg becomes fertilized by the sperm. This results in a full set of chromosomes. Somatic Cells All body cells except for sex cells that have diploid chromosomes Diploid Diploid means they have chromosome found in pairs, written as 2n

Homologous Chromosomes Similar chromosomes that are found in pairs. The paired chromosomes come from the mother and father. * Human body cells have 46 chromosomes each * Human body cells have 23 homologous pairs Meiosis and Fertilization Important for survival of many species, because these processes result in genetic variation of offspring. Meiosis A kind of cell division that results in gametes (sex cells) with half the number of chromosomes.

A. Gametes do not have homologous pairs, but instead they have only half the chromosomes from each pair. Gametes are referred to as haploid (n). B. When fertilization occurs, the zygote will have a normal number of chromosomes (2n). C. In meiosis, specialized cells divide 2 times producing 4 daughter cells.

Meiosis Parent cell – chromosome pair Chromosomes copied 1st division - pairs split 2nd division – produces 4 gamete cells with ½ the original no. of chromosomes

Mitosis vs. Meiosis