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The Process ESLR: To become critical thinkers STANDARD: Students know meiosis is an early step in sexual reproduction in which the pairs of chromosomes separate and segregate randomly during cell division to produce gametes containing one chromosome of each type. Review MEIOSIS – the process of cell division in which the number of chromosomes are reduced to half through a process of separating homologous pairs. Review MEIOSIS – the process of cell division in which the number of chromosomes are reduced to half through a process of separating homologous pairs. Diploid – Haploid - Review MEIOSIS – the process of cell division in which the number of chromosomes are reduced to half through a process of separating homologous pairs. Diploid – 2 copies of each chromosome Haploid - 1 copies of each chromosome Meiosis A cell division forming haploid cells Goal: reduce genetic material by half Why? from mom from dad child too much! meiosis reduces genetic content Phase: Interphase Cells grow and undergo a round of DNA replication forming duplicate chromosomes Nucleus MEIOSIS 1 Phase: Prophase 1 Each chromosome pairs with its corresponding homologous chromosome – (homolog) to form a tetrad (4 chromatids) MEIOSIS 1 Phase: Prophase 1 A A B C a b c D D d B C E F E F e f a b c d e f They exchange parts of chromosomes – Crossing Over MEIOSIS 1 A a B C C c D D E F b c d E F e f Phase: Prophase 1 Crossing over d e f MEIOSIS 1 a A B b C C B c D D E F a A d E F e f b c Phase: Prophase 1 Crossing over •Generates diversity d e f MEIOSIS 1 Phase: Metaphase 1 Spindle fibers attach to the chromosomes Spindle fibers MEIOSIS 1 Phase: Anaphase 1 Fibers pull the homologous chromosomes toward the opposite ends of the cell MEIOSIS 1 Phase: Telophase 1 & Cytokinesis Nuclear envelope Nuclear membrane forms and the cell separates into two cells MEIOSIS II Phase: Prophase II MEIOSIS II Phase: Metaphase II Chromosomes line up across the center of the cell similar to mitosis MEIOSIS II Phase: Anaphase II Sister chromatids separate and move toward the opposite ends of the cell MEIOSIS II Phase: Telophase II Nuclear membranes Chromosomes uncoil Spindles disappear MEIOSIS II Phase: Cytokinesis Four haploid cells One copy of each chromosome