Like Mitosis, but half as good! 11-4 Meiosis Like Mitosis, but half as good! Interactive pgs. 275-278

Genes Genes are located on chromosomes in the nucleus 1) Organisms must inherit a single copy of every gene from each of its “parents” 2) In gamete formation, two sets of genes must be separated from each other Genes

Each organism has 2 sets of homologous chromosomes (1 set from each parent) Fruit flies have 8 chromosomes (4 from each parent) Diploid cells contain both sets (2N) Ex: fruit flies have 2N=8 Haploid cells have only one set (N) Gametes or sex cells Ex: fruit flies have N=4 Chromosome Number

Homologous Chromosomes: Paternal Maternal Homologous chromosomes sister chromatids Tetrad

Cell division in which the number of chromosomes in a cell is cut in half (diploid  haploid) Leads to the production of haploid gametes Two stages: Meiosis I Meiosis II Meiosis

Meiosis I Interphase I: chromosomes are duplicated Prophase I: corresponding homologous chromosomes form a tetrad Crossing over: chromosomes exchange portions of their chromatids Leads to new combinations of alleles During this stage, homologous chromosomes separate and 2 new haploid cells are formed Meiosis I

Meiosis II NO replication of chromosomes Chromatids separate and the 2 haploid cells divide to form 4 haploid daughter cells Meiosis II

Use pgs. 276-277 to label the stages (a-j) Interphase I Prophase I Metaphase I Anaphase I Telophase I & Cytokinesis Telophase II & Cytokinesis Prophase II Metaphase II Anaphase II 4 haploid cells

Crossing Over (during Prophase I)

Males: SPERMATOGENESIS results in 4 equal sized gametes called sperm Females: OOGENESIS results in 1 large egg and 3 other nonuseful cells called polar bodies Gamete Formation

Comparing Mitosis & Meiosis Production of 2 genetically IDENTICAL diploid cells Body cells Meiosis Production of 4 genetically DIFFERENT haploid cells Makes gametes (sex cells) Comparing Mitosis & Meiosis