The Meiosis Animation Meiosis is the division of germ cells Germ cells are diploid cells that will divide to form gametes Male gametes Sperm cells = male gametes Created by meiosis in male testes Female gametes Egg cells (ova) = female gametes Created by meiosis in female testes Importance: Meiosis reduces the chromosome number by half If meiosis did not occur, egg and sperm would each be diploid 46 chromosomes in the sperm would combine with 46 chromosomes in the egg to create a zygote with 92 chromosomes
Here is a diploid cell. 46 strands of chromatin. Orange = from father; Green = from mother During the S stage of interphase, the chromatin strands are duplicated. There are now 92 strands of chromatin.
During prophase I, the nucleus dissolves
During prophase I, the chromatin coils into chromosomes Notice there are two of every chromosome number…one you inherited from your mother and one from your father. 1 5 12 9 8 22 13 15 6 11 11 17 18 19 13 14 18 2 6 1 7 21 9 17 15 10 4 23 16 7 22 10 3 19 3 21 16 4 5 20 14 2 20 23 8 12
This creates 23 tetrads. Tetrads have 4 chromatids each. During prophase I, synapsis occurs. Spindle fibers pull the pairing of homologous chromosomes to each other. 1 5 12 9 8 22 13 15 6 11 11 17 18 19 13 14 18 2 6 1 7 21 9 17 15 10 4 23 16 7 22 10 3 19 3 21 16 4 5 20 14 2 tetrad 20 23 8 12 tetrad This creates 23 tetrads. Tetrads have 4 chromatids each. Crossing over would also occur here.
During metaphase I, the spindle fibers pull the tetrads to the cell equator 8 8 15 15 11 11 17 17 18 18 19 19 13 13 6 1 1 6 7 7 9 9 10 10 16 16 22 22 3 3 21 21 4 4 5 5 14 14 2 2 20 20 23 23 12 12
During anaphase I, the homologous chromosomes are separated. 8 8 15 15 1 1 11 11 During anaphase I, the homologous chromosomes are separated. 18 18 After telophase I, cytokinesis divides the cell into two 13 13 19 19 10 10 17 17 6 6 7 7 16 16 22 22 3 3 5 5 14 14 9 9 4 4 21 21 20 20 23 23 2 2 12 12
Jump to metaphase II During anaphase II, the sister chromatids are pulled apart During telophase II and cytokinesis, the cytoplasm divides The chromatids unwind back into strands of chromatin You now have 4 haploid cells