Pair of homologous 5 µm chromosomes Centromere Sister chromatids Key DESCRIPTION OF CHROMOSOMES Maternal set of chromosomes (n = 3) 2n = 6 Paternal set of chromosomes (n = 3) Two sister chromatids of one replicated chromosomes Centromere Two nonsister Pair of homologous chromatids in chromosomes a homologous pair (one from each set) Key Haploid gametes (n = 23) Haploid (n) Ovum (n) Diploid (2n) Sperm cell (n) MEIOSIS FERTILIZATION Ovary Testis Diploid zygote (2n = 46) Mitosis and development Multicellular diploid adults (2n = 46) HUMAN LIFE CYCLE Interphase Homologous pair of chromosomes in diploid parent cell MEIOSIS Chromosomes replicate Homologous pair of replicated chromosomes Sister chromatids Diploid cell with replicated chromosomes Meiosis I Homologous chromosomes separate Haploid cells with replicated chromosomes Meiosis II Sister chromatids separate Haploid cells with unreplicated chromosomes INTERPHASE MEIOSIS I: Separates homologous chromosomes PROPHASE I METAPHASE I ANAPHASE I Centrosomes Centromere Sister chromatids (with centriole pairs) (with kinetochore) remain attached Sister Chiasmata chromatids Metaphase Spindle plate Nuclear envelope Chromatin Tetrad Microtubule Homologous attached to chromosomes kinetochore separate Chromosomes duplicate Homologous chromosomes Tetrads line up Pairs of homologous (red and blue) pair and chromosomes split up exchange segments; 2n = 6 in this example MEIOSIS II: Separates sister chromatids TELOPHASE I AND TELOPHASE II AND PROPHASE II METAPHASE II ANAPHASE II CYTOKINESIS CYTOKINESIS Cleavage Haploid daughter cells furrow Sister chromatids forming separate Two haploid cells form; chromosomes During another round of cell division, the sister chromatids finally separate; are still double four haploid daughter cells result, containing single chromosomes MITOSIS MEIOSIS Parent cell Chiasma (site of MEIOSIS I (before chromosome replication) crossing over) Propase Prophase I Chromosome Chromosome replication replication Tetrad formed by Duplicated chromosome synapsis of homologous 2n = 6 (two sister chromatids) chromosomes Chromosomes Tetrads Metaphase positioned at the positioned at the Metaphase I metaphase plate metaphase plate Anaphase Sister chromatids Homologues Anaphase I Telophase separate during separate Telophase I anaphase during Haploid anaphase I; n = 3 sister chromatids Daughter remain together cells of meiosis I 2n 2n MEIOSIS II Daughter cells of mitosis n n n n Daughter cells of meiosis II Sister chromatids separate during anaphase II Key Maternal set of chromosomes Possibility 1 Possibility 2 Paternal set of chromosomes Two equally probable arrangements of chromosomes at metaphase I Metaphase II Daughter cells Combination 1 Combination 2 Combination 3 Combination 4 Meiosis: independent distribution chromosomes Prophase I Nonsister of meiosis chromatids Tetrad Chiasma, site of crossing over Metaphase I Metaphase II Daughter cells Recombinant chromosomes Meiosis: crossing over.