BIO 123 Chapter 9 Notes (Part 1/2)
BIO 123 Chapter 9 Notes (Part 1/2) BIOL 123
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This 6 page Class Notes was uploaded by Amber Logan on Tuesday November 3, 2015. The Class Notes belongs to BIOL 123 at University of New Mexico taught by Dr. Dorothy C. Scholl in Fall 2015. Since its upload, it has received 74 views. For similar materials see Biology for Health Related Sciences and Non-Majors in Biology at University of New Mexico.
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Date Created: 11/03/15
Chapter 9 Notes Sexual Reproduction Genetic Diversity and Inheritance Eukaryotic cells can produce either 0 Asexually mitosis 9 produces genetically identical daughter cells 0 Sexually meiosis 9 produces genetically different offspring through fusion of gametes 0 Key terms 0 Trait any physical feature of an individual Often called phenotypic traits observable traits 0 Gene heritable feature located on chromosomes that are responsible for an organism s traits Alleles alternative forms of a gene 0 Le 2 common alleles for eye color are brown and blue 0 Mutation any random change in the sequence of DNA nucleotides 91 The Origins and Importance of Sexual Reproduction The evolution of sexual reproduction might have come from endosymbiosis and the evolution of mitochondria o Mitochondria are very efficient at producing ATP by oxidative phosphorylation 0 But this process produces freeradicals reactive oxygen species that can damage our cells and DNA 0 It would be detrimental is our cells only had 1 copy of a gene and got damaged by free radicals 9 eukaryotes evolved sexual reproduction a process that combines the genomes of 2 individuals resulting in 2 copies of each gene 0 Benefits of sexual reproduction 0 Having 2 copies of 1 gene explained above decreases chances of cells being permanently damaged by freeradicals 0 Improved evolution by natural selection because of the increased genetic diversity within populations Deleterious alleles alleles that are less fit than others 0 When these are combined within 1 individual natural selection will work against and remove them from the population Remember natural selection acts upon the traits of an individual but only populations can evolve over time 0 Meiosis 0 May have evolved through small changes in mitosis o Is basically 2 rounds of mitosis w a couple of small adjustments 0 Results in 4 haploid n 23 daughter cells called gametes Gametes from oppositesex parents can fuse to form a diploid n 46 2n 23 zygote which will eventually grow into an individual organism 92 The Steps of Meiosis lt n lt6 39 o 3993 Image 1 lnterphase 0 DNA is replicated during S phase Meiosis I o Prophase I Same as Prophase of Mitosis Chromatin condenses into chromosomes 0 Mitotic spindle begins to form 0 Nuclear membrane breaks down Homologous chromosomes join together to form a tetrad Homologous pairs get so close to one another that the sister chromatids touch and swap DNA crossing over 0 Metaphase I Homologous pairs line up along equator of cell 0 Anaphase I Homologous chromosome pairs are pulled apart 0 vs Mitosis sister chromatids are separated o Telophase I Similar to Telophase of Mitosis chromosomes are pulled to opposite ends of cell Result 2 haploid daughter cells 0 Are haploid because even though these cells technically have 46 chromosomes they only have 12 of the genetic material of the original cell because they either have the paternal or maternal chromosome pair one set of chromosomes homologous set of chromosomes homologous chromosomes crossing over PROPHASE I I METAPHASE I AIIAPHASE I TELOPHASE I Image 2 Meiosis II o Prophase ll Mitotic spindle begins to form 0 Metaphase ll Homologous chromosomes line up along equator of cell 0 Anaphase ll Sister chromatids are pulled apart 0 Telophase ll Same as Telophase l Result 4 genetically diverse haploid gametes IEIOSIS ll haploid numbertn of unduplicated chromosomes PROPHASE II METAPHASE II ANAPHASE ll TELOPHASE II Image 3 Gamete Formation in Humans Gametogenesis process of forming gametes in both males and females 0 Begins w diploid stem cell Precursor sex cell that gives rise to primary spermatocyteoocyte o Nondisjunction when the homologous chromosomessister chromatids fail to separate properly during disjunction Anaphase lll Result in chromosomal defects many of which are fatal 0 Eg trisomy 21 3 copies of chromosome 21 9 Down Syndrome Spermatogenesis process of forming male gametes o Takes place in testes o Begins during puberty and continues throughout a male s life about 100 million sperm are produced daily 0 Process 1 Mitosis produces 1 primary spermatocyte 2 Meiosis l produces 2 secondary spermatocytes 3 Meiosis ll produces 4 daughter cell each w 23 chromosomes 4 Daughter cells continue to develop eventually separating themselves and growing their flagella Oogenesis process of forming female gametesdevelopment of eggs 0 Takes place in the ovaries n Benins at 7 months in tern develnnment 0 Process 1 Primary oocyte begins Meiosis in ovary follicles process remains in Prophase un pubeny 0 A female may have 1 million primary oocytes at birth but this number will drop by puberty 2 Once a female reaches puberty 0 Every 28 days a primary oocyte will complete Meiosis I forming a secondary oocyte 0 Secondary oocyte will continue to Meiosis process stops at Metaphase unless it becomes fertilized 3 If egg is fertilized completes Meiosis II o 1 round of meiosis only produces 1 viable egg the other 3 daughter cells are called polar bodies and will eventually die Spermatogonium Oogonium GrowthMaturation Primary Primary 39 X spermatocyte oocyte Secondary 73 Secondary 39 lt spermatocytes 74 I oocyte First polar I I Meiosis II I bOd Spermatids 39 Ootid Second polar body Differentiation flt 39lt f lt Ovum Spermatozoa Image 4 Note First polar body in oogenesis goes on to become 2 smaller polar bodies which will eventually disintegrate 93 Meiosis and the Generation of Genetic Diversity 0 3 ways to enhance genetic diversity 1 Crossing over Occurs during Prophase What happens aees on homologous chromosomes can switch places to make new combinations I Is cnmnlefelv random IIIIIHIIIII Homologous Pair Crossing Over Gametes Image 5 2 Independent Assortment What happens chromosomes randomly orient themselves when they line up on metaphase plate during Metaphase Possibility 1 Possibility 2 Two equally probable I k i arrangements of chromosomes at 39 39 metaphase I 39 4 31 Metaphase II 6 J C x J Combination 1 Combirlration 2 Combination 3 Combination 4 Image 6 3 Random fertilization Humans have 84 million possible combinations of maternalpaternal chromosomes in our gametes 9 you never know what kind of new combinations you re going to get when an egg is fertilized by a sperm Picture Credits Image 1 My personal lecture notes Image 2 httpnewmajors naltumblrcom Image 3 httpbiologytutorvistacomceIImeiosishtml Image 4 httpwwwbiologyexams4ucom201306differencebetweenspermatogenesisandhtml Image 5 httpwwwvcebioninjacomauaos3heredityceIIreproductionmeiosishtml Image 6 httpswwwstudybluecomnotesnotengeneticsindependentassortmentdeck7893704
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