Chapter 7 Lesson 2 “Production of Reproductive Cells”

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

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

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

n n 2n (zygote) ½ female info½ male info

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

III. Meiosis I (In males) (pg ) A. Interphase I -chromosomes are duplicated B. Prophase I -nuclear membrane dissolves -centrioles move apart -spindle forms -tetrads form (group of 4)

C. Metaphase I -tetrads line up at the equator -centrioles are found at the poles

D. Anaphase I -centromeres do not break -sister chromatids stay connected -separation of the homologous pair

E. Telophase I -cell begins to pinch -2 cells formed

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

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

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.