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Chapter 7 Lesson 2 “Production of Reproductive Cells”
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I. Chromosome Numbers and Characteristics A. Chromosomes 1. Different amounts in every organism a. Human b. Fruit Fly c. Dog 23 pairs 4 pairs 39 pairs
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2. Same #’s are always passed on. B. Diploid 1. Having 2 of each chromosome 2. 2n (n = # of paired chromosomes) so… 2n or 2(23) = 46 chromosomes 3. Homologue – 1 chromosome a. How many homologues? b. Combinations of different homologues determine specific traits. 2
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II. Meiosis Where do animal and plant cells get their homologues from? A. Haploid Sex Cells 1. Def – cells that contain ½ of a parents genetic information. a. Haploid cells = sperm/egg represented by “n” 2. Sexual Reproduction – 2 haploid cells fuse together to form a diploid cell. (zygote) forms mature multicellular organism Male and female reproduction zygote (single fertilized egg) parents
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n n 2n (zygote) ½ female info½ male info
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B. Def of Meiosis – the process by which haploid cells are produced. or the formation of sperm and egg only occurs in reproductive tissues provides the right # of chromosomes 1. 2 parts a. Meiosis I and Meiosis II
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III. Meiosis I (In males) (pg. 184-185) A. Interphase I -chromosomes are duplicated B. Prophase I -nuclear membrane dissolves -centrioles move apart -spindle forms -tetrads form (group of 4)
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C. Metaphase I -tetrads line up at the equator -centrioles are found at the poles
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D. Anaphase I -centromeres do not break -sister chromatids stay connected -separation of the homologous pair
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E. Telophase I -cell begins to pinch -2 cells formed
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IV. Meiosis II *Similar to mitosis A. Interphase – no DNA replication; brief B. Metaphase II – chromosomes move to the equator C. Anaphase II – centromeres split and sister chromatids move to the poles. D. Telophase II – cell pinches; 4 haploid cells are produced -cells now contain “n” 4 sperm cells
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V. Meiosis in Females (pg. 187) *Similar process but a couple different twists* 1. Go through meiosis when in the womb (approx. 12 weeks) 2. 1 cell survives per cycle A. Meiosis I 1. Cell divides; unequal sizes a. Large cell continues to meiosis II b. Small cell usually dies B. Meiosis II 2. Cell divides; unequal sizes a. Large cell can become fertilized (n) b. Small cell usually dies 1 egg cell
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VI. Why Meiosis? A. Produce haploid cells B. Continues life cycle C. Genetic Variation… 1. mitosis replica cells 2. meiosis variation of cells a. Allows change b. Better chance of survival (natural selection) c. Genetic Recombination – reshuffling of chromosomes and genetic information.
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