Meiosis PDF

MEIOSIS Variety is the Spice of Life! SEXUAL REPRODUCTION The production of offspring from the fusion of two sex cells ◻ Usually from two different parents ◻ The genetic makeup of the offspring is different from that of either parent ◻ TERMS TO KNOW ◻ SOMATIC CELLS: cells that perform mitosis ■...

MEIOSIS Variety is the Spice of Life! SEXUAL REPRODUCTION The production of offspring from the fusion of two sex cells ◻ Usually from two different parents ◻ The genetic makeup of the offspring is different from that of either parent ◻ TERMS TO KNOW ◻ SOMATIC CELLS: cells that perform mitosis ■ EXAMPLE: ◻ GAMETE CELLS: cells that perform meiosis ■ EXAMPLE: ◻ ◻ skin cells sex cells FERTILIZATION: when two gamete cells combine to form a single zygote cell ZYGOTE: the first cell of a new individual HOMOLOGOUS CHROMOSOMES ◻ ◻ Pairs of chromosomes that are similar in structure and carry similar genetic information You get one chromosome from your mother and one chromosome from your father CHROMOSOMES ◻ ◻ DIPLOID NUMBER The number of chromosomes in somatic cells There are 46 chromosomes in a typical human somatic cell HAPLOID NUMBER ◻ ◻ ◻ The number of chromosome in gamete cells The number of chromosomes in gamete cells is half the number of somatic cells There are 23 chromosomes in a typical human gamete cell FERTILIZATION MEIOSIS ◻ ◻ ◻ ◻ A form of cell division in which the resulting daughter cells have half the number of chromosomes as the parent cell There are two stages: Meiosis I and Meiosis II Results in the formation of four gamete cells It takes place only in reproductive tissue of sexually reproducing organisms MITOSIS VS. MEIOSIS MITOSIS MEIOSIS STAGES OF MEIOSIS MEISOSIS I ◻ ◻ ◻ ◻ Prophase I Metaphase I Anaphase I Telophase I MEIOSIS II ◻ ◻ ◻ ◻ Prophase II Metaphase II Anaphase II Telophase II PROPHASE I ◻ ◻ ◻ Similar events occur in prophase I of meiosis as in prophase of mitosis Chromosomes come together in homologous pairs The homologous pairing forms a TETRAD GENETIC VARIATION ◻ During PROPHASE I there is an event that occurs to ensure that you have genetic variability: ■ RECOMBINATION: the exchanging of genetic information called CROSSING OVER METAPHASE I – Further Genetic Variation ◻ ◻ The tetrads migrate towards the centre of the cell and align across the middle of the cell randomly RANDOM ASSORTMENT: chromosomes that come from the father will not stay together nor will chromosomes that come from the mother (aka Independent Assortment) ANAPHASE I The homologous chromosomes move to opposite poles of the cell Only ONE chromosome from each homologous pair will be found in each new daughter cell TELOPHASE I ◻ ◻ The cells begin to divide Each daughter cell has only one member of each original pair MEIOSIS II ◻ ◻ ◻ ◻ Begins immediately after Telophase I There is NO duplication of DNA between Meiosis I and Meiosis II The chromosomes still consist of sister chromatids, however, the sister chromatids are no longer identical Meiosis II continues on like Mitosis ◻ PROPHASE II🡪 METAPHASE II🡪 ANAPHASE II🡪 TELOPHASE II GAMETOGENESIS SPERMATOGENESIS ◻ ◻ ◻ The production of sperm cells There is even division of the cytoplasm at each stage of meiosis The final product is four SPERM cells ◻ ◻ ◻ OOGENESIS The production of egg cells The cytoplasm doesn’t divide equally at each stage of meiosis Final product is a single OVUM NON-DISJUNCTION ◻ ◻ ◻ ◻ The separation of chromosomes occurs incorrectly It can happen during Meiosis I or Meiosis II It results in a cell that can contain too many or too few chromosomes If that cell is involved in fertilization, the zygote will have an abnormal number of chromosomes NON-DISJUNCTION TRISOMY ◻ A chromosomal abnormality in which there are three homologous chromosomes MONOSOMY ◻ A chromosomal abnormality in which there is a single chromosome DOWN SYNDROME ◻ ◻ An individual that has three copies of chromosome number 21 These individuals experience physical and mental challenges TURNER SYNDROME ◻ ◻ An individual that has only one X chromosome These individuals are female in appearance but do not mature sexually and are sterile KLINEFELTER SYNDROME ◻ ◻ An individual with two X chromosomes and one Y chromosome These individuals are male in appearance with feminine body characteristics and are usually sterile