Cell+Division+II

= Describe meiosis in animal and plant cells giving special attention to the following:= =a. The stages of meiosis.= =b. The function of meiotic daughter cells and the organs where meiosis takes place.= =c. Contributions to genetic variation.=  There are 8 stages of meiosis: prophase I, metaphase I, anaphase I, telephase I, prophase II, metaphase II, anaphase II, and telephase II. In animals, meiosis occurs in the production of gametes, and in plants, when spores are produced. In prophase I, chromosomes condense, the spindles extend form the centriole pairs, and the nuclear membrane disappears. During prophase the centrioles move to opposite ends of the cell, and the spindles lengthen and extend toward the middle of the cell. The chromosomes align on the metaphase plate and the spindle fibers attach to the centromere in metaphase I. During anaphase I, the cell lengthens and homologs of each chromosome pair move to opposite poles. After the chromosomes reach the poles, eahc has a complete haploid set of chromosomes. During telephase I, a cleavage furrow appears, which eventually splits the cell in a process known as cytokinesis. (Danyelle S.) During prophase II DNA does not replicate, the centrioles duplicate. This occurs during the separation of the two members of the pair and then the daughter centrioles are perpendicular to each original centriole. The two pairs separate into two centrosomes. Then the nuclear envelope breaks down and the spindle apparatus forms. In metaphase II the chromosomes are aligned along a single plain of each cell. This stage ends when the centromeres connecting the pairs to each other break. Then in anaphase II the centromers separate, and the two chromatids of each chromosome moves to opposite poles on the spindle. Finally during telephase II the nuclear envelopes forms around each set of DNA and the cytoplasm divides. So, then the four haploid cells have formed one diploid cell. (Anna R.).