BIOL 101 Lecture Notes - Lecture 9: Sister Chromatids, Homologous Chromosome, Mendelian Inheritance
Document Summary
They have one version of each chromosome-haploid. Egg (ovum)-23 chromosomes and sperm (23 chromosomes) makes a zygote (diploid)-fertilization to have 46 chromosomes and 23 pairs. Reduce amount of genetic material by half-2n to 1n. Meiosis: only in gonads (ovaries and testes) Mitosis steps happens once and meiosis steps happen twice. Meiosis starts with a diploid cell a homologues and then there is a s phase where dna replicated and then you get two sister chromatids. Two major parts: meiosis cells divide twice. Meiosis 1-homologues-separate diploid (2n) to haploid (1n). One version of a chromosome in each cell. Meiosis 1-where all sexual reproduction variation occurs. Prophase 1-homologous chromosome link as they condense, forming tetrads. (crossing over occurs; variation) Metaphase 1-microtubles move homologous chromosomes to metaphase plate. Spindles are attached to centromeres and line up at the metaphase plate. Anaphase 1-micotrubles separate homologous chromosome (sister chromatids remain together). Telophase 1-two haploid daughter cells result from cytokinesis.