The phases of Meiosis start with-
Interphase: Growth 1- Initail period of intense cytoplasmic growth, synthesis- DNA synthesis or replication occurs, Growth 2- Prophase: Chromosomes condense, envelope disapears. Metaphase: Chromosomes line up on the midline of the dividing cell. Anaphase: Chromosomes begin to separate. Spindle fibers attach to centrioles. Telophase: Chromosomes drift to opposite poles nuclear envelopes form, chromosomes uncoil. Cytokinesis: Cleavage furrows and weakens- cytoplasm divide. A period of interkinesis- period between meiosis 1 and 2. Prophase 2: Chromosomes condense, envelope disapears. Metaphase 2: Chromosomes line up on the midline of the dividing cell. Anaphase 2: Chromosomes beigin to separate. Spindle fibers fibers attach to centrioles. Telophase 2: Chromosomes drift to opposite poles, nuclear envelopes forms, chromosomes uncoil. Cytokinesis 2: Cleavage furrows and weakends- cytoplasm. |
Spermatogenis
Begins with a diploid stem cell called a spermatogonium. the cell divides mitotically, yeiling two daughter cells. Only one becomes a matue sperm.
Spermatogonia become the primary spermatocytes. In meiosis 1 the primary spermatocyte divides into two haploid cells called secondary spermatocytes. In meiosis 2 dach secondary spermatocyte divides making two spermatids. For a quizlet on key vocab terms I learned in this chapter click the learn more button. |
Oogenis
The cellls in the ovary called oogonis, divide by mitosis and form primary oocytes. Those oocytes undergo meiosis . One oocyte recieves 95% of the cytoplasm, that cell becomes the secondary oocyte. The other recieves 5% those cells are called polar bodies. As the sceondary oocyte undergoes meiosis 2 the same cytoplasmic disportion takes place. The cell that receives 95% of the cyoplasm becomes the ootid.
|
Factors that contribute to genetic variation:In meiosis 1 each homologous pair of chromosomes is positioned indepently from the other pairs.
The number of combinations possible when chromosomes assort independenltly into gametes is represented by the equation 2^n. Exchage of genetic material between homologous chromosomes is known as crossing over(i.e. recombination). Random fertilization takes place in the uterin wall, one sperm fertilzes one egg. |