I. Reproduction A) Asexual 1 I. Reproduction A) Asexual 1. Many single-celled organisms reproduce by binary fission, budding 2. Some multicellular organisms can reproduce asexually, produce clones (offspring genetically identical to parent).

Binary fission in Bacteria Budding in Hydra Binary fission in Bacteria https://www.google.com/search?q=budding+in+hydra&safe=strict&espv=2&biw=1024&bih=613&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjk3b_jyqjRAhUPfiYKHRvJBaYQ_AUIBigB#imgrc=y4p8DrcFCFgJ2M%3A

B) Sexual reproduction 1. Most advanced orgs 2 B) Sexual reproduction 1. Most advanced orgs 2. Benefit: greater genetic variation=more resilient 3. SOME can self fertilize but most offspring are recombinants of parents genes 4. Fertilization: Male & Female gametes unite to form diploid zygote

II. Overview of Meiosis Occurs in gonads (sex cell producing glands): germ cells create gametes (Sex cells) Eggs formed by oogenesis and sperm by spermatogenesis in animals Gametes are Ovule and pollen in plants REDUCES chromosome # by half so offspring has correct # of chromosomes Produces haploid cells: contain HALF the correct number of chromosomes Somatic cells are Diploid; Gametes are haploid

C) Increases genetic diversity by: 1 C) Increases genetic diversity by: 1. Allowing for sexual fertilization (mixes genes) 2. Crossing over and independent assortment D) Chromosome Basics (Using humans as an example…) 1. Normal humans have 46 TOTAL chromosomes in each somatic cell (23 pairs, 1set from each parent) 2. Thus 23 chromosomes must come from each parent = 46 E) Meiosis is similar to doubled mitosis

Meiosis I Prophase I 1. DNA coils into chromosomes, spindle forms, nucleus & nucleolus dissolve 2. Synapsis-Pairs of homologous chromosomes line up to form a tetrad. Where they cross = chiasmata

3. Crossing over: Arms of crossed over chromatids break and swap 3. Crossing over: Arms of crossed over chromatids break and swap. Create RECOMBINANT chromosomes a) Can be a SINGLE or b) DOUBLE cross over *INCREASES GENETIC VARIETY IN GAMETES!

Metaphase I – Similar to mitosis, 1. Tetrads line up on equator 2. Random assortment on equator Independent Assortment: also increases genetic variation!)

C) Anaphase I 1. Tetrads separate (into 2 homologous pairs) and move to opposite poles (2 SETS of chromatids held tog by centromeres) 2. Centromeres do NOT split-homologous pairs still together

D) Telophase I and Cytokinesis I 1. Similar to mitosis 2 D) Telophase I and Cytokinesis I 1. Similar to mitosis 2. Result is 2 diploid cells

http://images.tutorvista.com/cms/images/123/meiosis-2.jpeg

Meiosis II – Identical to mitosis A) Prophase II – spindle forms in opp direction as meiosis I B) Metaphase II – Line up on equator, random C) Anaphase II - centromeres split, chromatids move to opposite poles D) Result after cytokinesis II is 4 haploid cells

V. Spermatogeneisis (in testes). Cells are modified into sperm http://static.fastbleep.com/assets/notes/image/9883_1.jpg

VI. Oogenesis- in ovaries A) Starts before birth but arrests in prophase I. Starts back up in puberty B) All resources go into 1 cell, other 3 become polar bodies

Fertilization – egg & sperm meet Result is 1 diploid cell=zygote From this pt on divides by MITOSIS into embryo etc