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Organism Survival cont.

Organism Survival cont. Growth, maintenance & reproduction III. Basic sexual life cycle revised. Interphase, Mitosis and Cytokinesis. Zygote. ?. Gametes and Fertilization. 2n. 4 haploid cells. n. Adult. Meiosis and Cytokinesis. What is the fate of a haploid cell?.

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Organism Survival cont.

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  1. Organism Survival cont. Growth, maintenance & reproduction III

  2. Basic sexual life cycle revised Interphase, Mitosis and Cytokinesis Zygote ? Gametes and Fertilization 2n 4 haploid cells n Adult Meiosis and Cytokinesis

  3. What is the fate of a haploid cell? Recall that meiosis and cytokinesis result in 4 genetically variable, haploid cells being produced from 1 diploid germ (reproductive) cell Differentiated haploid cell = Gamete (recall: differentiation is a change in structure for a particular function) Not all haploid (n) cells will mature (differentiate) to form gametes Variation in gamete maturation: • between genders of a species (male & female) Sperm – flagella for motility, +++ mitochondria for energy Egg – increased volume for biochemical support (e.g. nutrients)

  4. Spermatogenesis spermatids (haploid) secondary spermatocytes (haploid) spermato-gonium (diploid ) primary spermatocyte (diploid) Meiosis I, Cytoplasmic Division Meiosis II, Cytoplasmic Division Growth differentiation sperm (mature, haploid male gametes)

  5. three polar bodies (haploid) Oogenesis first polar body (haploid) oogonium (diploid) primary oocyte (diploid) differentiation secondary oocyte (haploid) ovum (haploid) Meiosis I, Cytoplasmic Division Meiosis II, Cytoplasmic Division Growth

  6. What is the fate of a haploid cell? Recall that meiosis and cytokinesis result in 4 genetically variable, haploid cells being produced from 1 diploid germ (reproductive) cell Differentiated haploid cell = Gamete (recall: differentiation is a change in structure for a particular function) Not all haploid (n) cells will mature (differentiate) to form gametes Variation in gamete maturation: • between genders of a species (male & female) • between species

  7. What is the fate of a haploid cell? Recall that meiosis and cytokinesis result in 4 genetically variable, haploid cells being produced from 1 diploid germ (reproductive) cell Differentiated haploid cell = Gamete (recall: differentiation is a change in structure for a particular function) Not all haploid (n) cells will mature (differentiate) to form gametes Variation in maturation: • between genders of a species (male & female) • between species • between plants and animals

  8. mitosis adult zygote Diploid meiosis fertilization Haploid gametes Ovules and pollen Plant Sexual Life Cycle BIOL 102 Animal Sexual Life Cycle mitosis adult zygote Diploid fertilization meiosis Haploid gametes Egg (ovum) and sperm fertilization meiosis

  9. What is the fate of a gamete? Male and female gametes unite The 2 haploid nuclei fuse, producing a diploid nucleus (recall homologous chromosome pairs) in the zygote (new cell) = Fertilization Fertilization: >> restores chromosome number (n 23 + n 23 = 2n 46) >> introduces further genetic variation as gametes combine randomly Meiosis, the differentiation of gametes and fertilization, define sexual reproduction

  10. Sexual Reproduction Offspring are genetically variable as they inherit new combinations of alleles (versions of the same gene) (which drives the process of evolution) >> Crossing Over (Recombination) of non-sister chromatids in Prophase I >> Random Alignment (Independent Assortment) of chromosomes in Metaphase I (Anaphase I) >> Random combination of gametes at fertilization Dominates the life cycles of multicellular Eukaryotes

  11. Sexual life cycle completed Fertilization zygote 2n gametes n Mitosis and cytokinesis n new cycle 2n Differentiation n 2n Meiosis and cytokinesis Growth and maintenance n n female adult n n male germ cell n 2n n 2n n n female germ cell n n

  12. Asexual Reproduction Reproduction in the absence of meiosis, gamete formation and fertilization >> offspring are identical (genetic clones) to each other and to the single parent By what process do you think the cells of the offspring are produced? Apart from growth and maintenance, Mitosis also functions in asexual reproduction Dominates the unicellular eukaryotes (protistans – Why?) Common in plants and fungi, and rare in animals

  13. Functions Asexual reproduction (clones) Growth, repair Occurs in somatic cells Produces genetically identical cells Process One nuclear division Chromosome number maintained 2 diploid daughter cells Prophase – homologous pairs do not interact Metaphase – chromosomes align Anaphase – separates sister chromatids Function Sexual reproduction Occurs in germ cells Produces genetically variable cells Process 2 nuclear divisions Chromosome number halved (reduction division) 4 haploid daughter cells Prophase I – crossing over occurs Metaphase I – homologous pairs align for random assortment Anaphase I – separates homologous pairs Anaphase II – separates sister chromatids Mitosis Vs. Meiosis

  14. Starr and Taggart: The Unity and Diversity of Life Chapter 9 (Cell Division and Mitosis) Chapter 10 (Meiosis) www.ukzn.ac.za/biology/BIOL101SmallerSideofLife256.aspx

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