(but not the exciting bits) SEX (but not the exciting bits)

Definition of sexual reproduction A pattern of reproduction involving fusion of cells from two parents (fertilization). Fusing two cells results in twice as many chromosomes per cell. Therefore, sexual reproduction also includes a process to reduce chromosome number by half (meiosis).

Vocabulary Gametes: specialized cells that unite in fertilization (e.g. sperm, eggs) Zygote: the cell produced by fertilization Haploid: the number of chromosomes in a gamete (symbolized n) Diploid: the number of chromosomes in a zygote (symbolized 2n)

Species n 2n Mosquito 3 6 Rice plant 12 24 Alligator 16 32 Human 23 46 Every species has characteristic haploid and diploid chromosome numbers Species n 2n Mosquito 3 6 Rice plant 12 24 Alligator 16 32 Human 23 46 Potato 48 Dog 39 78 Carp 52 104

Diplontic life cycle Animals The mature organism is diploid. Mitosis allows these cells to divide so the organism can grow. Meiosis produces gametes. There is no mitosis in the haploid state.

Figure 9.12 Fertilization and Meiosis Alternate in Sexual Reproduction Gametes Male (n) Female (n) HAPLOID (n) Meiosis Fertilization DIPLOID (2n) Zygote Elephant (Loxodonta africana) Adult (2n)

Haplontic life cycle Fungi The mature organism is all haploid. Mitosis allows these haploid cells to divide so the organism can grow. Gametes are produced by mitosis. The zygote is the only diploid cell. There is no mitosis in the diploid state; the first thing the zygote does is go through meiosis, back to the haploid condition.

Figure 9.12 Fertilization and Meiosis Alternate in Sexual Reproduction Adult (n) Gametes (n) (n) Spore (n) HAPLOID (n) Meiosis Fertilization DIPLOID (2n) Fungus (Rhizopus oligosporus) Zygote (2n)

Alternation of Generations Plants Mitosis occurs in both haploid and diploid states. There is a multicellular body in both states. Sporophyte: a diploid body, developed by mitosis from a zygote, producing spores by meiosis. Gametophyte: a haploid body producing gametes (by mitosis)

Figure 9.12 Fertilization and Meiosis Alternate in Sexual Reproduction Gametophyte (n) Spore (n) Gametes Male (n) Female (n) HAPLOID (n) Fertilization Meiosis DIPLOID (2n) Sporangium Zygote Sporophyte (2n) Fern (Osmunda cinnamomcea)

Reading Assignment Chapter 9: pp. 165 – 171 Especially study the diagrams of meiosis on pp. 168-169 and 170-171, which are not discussed in this PowerPoint presentation.