Organism Survival cont. Growth, maintenance & reproduction III

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

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) What is the fate of a haploid cell?

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

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

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

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

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

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

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

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

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

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 Mitosis Vs. Meiosis 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

Starr and Taggart: The Unity and Diversity of Life Chapter 9 (Cell Division and Mitosis) Chapter 10 (Meiosis)