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Lecture 30

BIO 201 Lecture 30: Meiosis

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Biological Sciences
BIO 201
Lara Hutson

BIO 201 Dr. Lara Hutson Lecture 30 Notes 4/19/17 Asexual vs. Sexual Reproduction ● Asexual ○ Fission and mitosis (budding) ■ Yeast, protists, some multicellular organisms ○ Duplication of one genome followed by cell division or budding → 2nd generation cells are genetically identical* to parents and each other ■ *assuming DNA replication is perfect ■ Very little change from generation to generation ● Sexual ○ Combine genetic material from two parents → next generation is genetically distinct from parents and from each other ○ Advantage: diversity!!! ○ Problem: how to maintain appropriate chromosome numbers from one generation to the next ○ Solution: halves genomes before combining → MEIOSIS Life Cycles of a Sexually-Reproducing Diploid ● Multicellular diploid adults (2n = 46) ● Form haploid germ cells (egg and sperm) via meiosis (n = 23) ● Coming together of egg (n) and sperm (n) (fertilization) → formation of diploid zygote (2n) → mitosis (2n) → multicellular diploid organism (2n) Meiosis I 1. A. Metaphase I: Chromosome align on Metaphase I plate. Homologs adjacent to each other (synapsis) B. Homologs exchange DNA (chiasma) 2. Anaphase I: Homologous chromosomes segregate (sister chromatids remain together!) 3. Cytokinesis I Meiosis II 4. Metaphase II: Chromosomes align on metaphase plate 5. Anaphase II: Sister chromatids separate 6. Cytokinesis II ● Independent Assortment of Chromosomes Example: ○ Diploid (2n) ○ 3 chromosomes ● Number of different combinations: (# of chromosomes) ○ (# of homologs) ○ 2 = 8 ○ All distinct gametes! ● Diploid organism, 23 chromosomes: ○ Meiosis → 2 possible genetically distinct haploid gametes (8,388,608) ○ Fertilization → (2 )(2 )
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