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1 Reproduction and Meiosis. 2 Reproduction Reproductionthe process of producing offspring –Asexualone parent, offspring are genetically identical to parent.

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Presentation on theme: "1 Reproduction and Meiosis. 2 Reproduction Reproductionthe process of producing offspring –Asexualone parent, offspring are genetically identical to parent."— Presentation transcript:

1 1 Reproduction and Meiosis

2 2 Reproduction Reproductionthe process of producing offspring –Asexualone parent, offspring are genetically identical to parent Budding, fission, fragmentation, parthenogenesis –Sexualtwo parents, offspring genetically different from parents Parents produce gametes –Females=egg –Males=sperm Two gametes combine=fertilization; produces first cell called the zygote Offspring will have traits of both parents

3 3 Homologous Chromosomes Each species has a characteristic number of chromosomes –Humans=46; dogs=78; fruit flies=8 Chromosomes come in pairshomologous chromosomes –Chromosomes with the same size, shape, and carry the codes for the same genes –Each chromosome in a homologous pair comes from one of the parents In humans, 23 chromosomes come from mom and 23 from dad

4 4 Meiosis Form of cell division that produces 4 daughter cells with half the number of chromosomes as the parent cell 2 distinct stages –Meiosis I Prophase I, Metaphase I, Anaphase I, Telophase I –Meiosis II Prophase II, Metaphase II, Anaphase II, Telophase II

5 5 Meiosis I Prophase I –Chromosomes condense –Homologous chromosomes pair up –Crossing over Chromatids exchange genetic material Increases genetic variability

6 6 Meiosis I Metaphase I –Homologous chromosomes line up along equator of cell Anaphase I –Homologous chromosomes move apart, pulled by spindle fibers Telophase I –Cytoplasm divides, resulting in two cells with the same number of chromosomes as parent

7 7 Meiosis II Prophase II Metaphase II Anaphase II Telophase II 4 different haploid cells

8 8 Results of Meiosis Gametes (egg & sperm) form Four haploid cells with one copy of each chromosome One allele of each gene Different combinations of alleles for different genes along the chromosome

9 9 MitosisMeiosis Number of divisions 12 Number of daughter cells 24 Genetically identical? YesNo Chromosome # Same as parent Half of parent Where Body cells Sex cells When Throughout life At sexual maturity Role Growth and Repair Sexual Reproduction Mitosis vs Meiosis

10 10 Gamete Production Gametes have half the number of chromosomes of the organism –Sperm (23 chromosomes) + Egg (23 chromosomes) = Human (46 chromosomes) Diploid (2n) –A cell with two of each chromosome, which are in pairs {FULL set} Haploid (n) –A cell with only one of each chromosome {half set}

11 11 Gamete Production: Sperm Occurs in the testesOccurs in the testes Two divisions produce 4 spermatidsTwo divisions produce 4 spermatids Spermatids mature into spermSpermatids mature into sperm Men produce about 250,000,000 sperm per dayMen produce about 250,000,000 sperm per day

12 12 Gamete Production: Egg Occurs in the ovariesOccurs in the ovaries Two divisions produce 3 polar bodies that die and 1 eggTwo divisions produce 3 polar bodies that die and 1 egg Polar bodies die because of unequal division of cytoplasmPolar bodies die because of unequal division of cytoplasm Immature egg called oocyteImmature egg called oocyte Starting at puberty, one oocyte matures into an ovum (egg) every 28 daysStarting at puberty, one oocyte matures into an ovum (egg) every 28 days


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