Unit 6 - Bio

• Meiosis: The form of cell division where the number of chromosomes in a cell is reduced by half
• Haploid: one set of chromosomes (n)
• Meiosis is sexual reproduction
• Two divisions (meiosis 1 and Meiosis 2)
• Diploid: two sets of chromosomes (2n)
• Gametes are sex cells and aa form of Haploid
• Sex cells divide to produce gametes (sperm or egg)
• Male: Spermatogenesis - sperm
• Female: Oogenesis - egg or ova
• Homologous chromosomes line up in Metaphase I
• Nondisjunction: When gametes are forming, some chromosomes might get left behind, resulting in a gamete with one too many or too few chromosomes
• Nondisjunction in Anaphase I: Homologous chromosomes don't separate, resulting in all 4 daughter cells being affected
• Nondisjunction in Anaphase II: Sister chromatids don't separate, resulting in only 2 daughter cells being affected
• Trisomy-21 (Down Syndrome): nondisjunction when child gets an extra 21st chromosome
• Monosomy (Turner's Syndrome): Child has an absence of one sex chromosome = XO (karyotype), resulting in abnormally short, sterile females
• Trisomy (Klinefelter's Syndrome) - One extra sex chromosome = XXY (karyotype), resulting in sterile, mentally challenged males
• Tetrad - Formed when homologous chromosomes come together (two chromosomes and four chromatids
• Synapsis - pairing of homologous chromosomes forming a tetrad
• Crossing over - Chromatids of tetrad exchange parts, only occurs in Prophase I
• Independent assortment is when homologous pairs line up at the center randomly, and occurs during Metaphase I