Reproduction Valentine’s Day Perfect time to introduce the next subject in class

Biology, 9th ed,Sylvia Mader Chapter 09 Asexual Reproduction One parent The prokaryotic chromosome is a ring of DNA Binary fission Cell splits in two Produces two genetically identical daughter cells, exactly like the original– asexual reproduction The Cell Cycle

Binary Fission The Cell Cycle Biology, 9th ed,Sylvia Mader Chapter 09 Slide #3 Binary Fission The Cell Cycle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. chromosome 1. Attachment of chromosome to a special plasma membrane site indicates that this bacterium is about to divide. cell wall plasma membrane cytoplasm 2. The cell is preparing for binary fission by enlarging its cell wall, plasma membrane, and overall volume. 3. DNA replication has produced two identical chromosomes. Cell wall and plasma membrane begin to grow inward. 4. As the cell elongates, the chromosomes are pulled apart. Cytoplasm is being distributed evenly. 5. New cell wall and plasma membrane has divided the daughter cells. © Dennis Kunkel Microscopy, Inc./Visuals Unlimited SEM 2,345X

Sexual Reproduction Two parents Sexual Reproduction Cell splits twice Produces four daughter cells, genetically different from the parent and each other –meiosis Increases genetic variation

Haploid vs. Diploid HAPLOID 1n One copy of each chromosome DIPLOID 2n Two copies of each chromosome Homologous chromosomes

Chromosome Structure

Homologous Chromosomes Biology, 9th ed,Sylvia Mader Chapter 10 Homologous Chromosomes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. Sister chromatids nonsister chromatids duplication duplication kinetochore centromere chromosome homologous pair chromosome paternal chromosome maternal chromosome b. a: © L. Willatt/Photo Researchers, Inc. Meiosis & Sexual Reproduction

Biology, 9th ed,Sylvia Mader Overview of Meiosis Chapter 10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Diploid parent cell 2n = 4 Meiosis & Sexual Reproduction

Meiosis & Sexual Reproduction synapse and then separate. Biology, 9th ed,Sylvia Mader Overview of Meiosis Chapter 10 Slide #9 Meiosis & Sexual Reproduction Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. centrioles nucleolus centromere chromosome duplication 2n = 4 2n = 4 MEIOSISI Homologous pairs synapse and then separate. 9

Overview of Meiosis Meiosis & Sexual Reproduction 10 Biology, 9th ed,Sylvia Mader Overview of Meiosis Chapter 10 Slide #10 Meiosis & Sexual Reproduction Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. First division Second division Four haploid daughter cells centrioles nucleolus sister chromatids centromere synapsis chromosome duplication 2n = 4 2n = 4 n = 2 n = 2 MEIOSISI Homologous pairs synapse and then separate. MEIOSISII Sister chromatids separate, becoming daughter chromosomes. 10

Genetic Variation For humans - 23 pairs of chromosomes: Independent Assortment Crossing Over Random Fertilization (8 million)(8 million) = 64 trillion possible offspring

Independent Assortment Biology, 9th ed,Sylvia Mader Chapter 10 Independent Assortment Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Combination 7 Combination 3 Combination 5 Combination 1 Combination 2 Combination 4 Combination 6 Combination 8 There is a 50/50 chance that gamete gets maternal/ paternal homologous chromosome # of possible gametes = 223 >8 million possible gamete combinations Meiosis & Sexual Reproduction

Crossing Over Occurs During Meiosis I Biology, 9th ed,Sylvia Mader Chapter 10 Crossing Over Occurs During Meiosis I Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. sister chromatids of a chromosome sister chromatids of its homologue Homologous chromosomes swap genes during prophase I Crossing over increases genetic variation even more A A a a A a B B b b B b chiasmata of nonsister chromatids 1 and 3 c C C c C c D D d d D d 1 2 3 4 1 2 3 4 1 2 3 4 Bivalent forms Crossing-over has occurred Daughter chromosomes a. b. c. d. Meiosis & Sexual Reproduction