Biology 1101 Week 5 Notes
Biology 1101 Week 5 Notes BIOLOGY 1101 - 0100
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BIOLOGY 1101 - 0100
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This 5 page Class Notes was uploaded by Alexa Notetaker on Tuesday February 9, 2016. The Class Notes belongs to BIOLOGY 1101 - 0100 at Ohio State University taught by Dr. Kristin Smock in Spring 2016. Since its upload, it has received 242 views. For similar materials see Biology in Biology at Ohio State University.
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Date Created: 02/09/16
Biology 1101 Week 5 Notes Human cells: • Sex cells (gametes) have one set of chromosomes o Haploid (n) o 23 total chromosomes o produced by meiosis • Gametes combine their chromosomes during fertilization to make a zygote o Becomes a diploid cell Meiosis have the chromosome #: • Solution: produce gametes by meiosis o Halves the chromosome number o Creates haploid cells (1 set of chromosomes) • Fertilization restores the __ number o Egg (n) + Sperm (n) = zygote (2n) Meiosis overview: • Requires 2 nuclear divisions o Meiosis I halves number of chromosomes and shuffles genetic information o Meiosis II produces 4 haploid cells § Must divide nucleus TWICE to get haploid cells § Sex cells (gametes) • Germs cells are the diploid cells in body t o go under meiosis • Germ cells are located in the ovaries and the testes Meiosis overview: • Homologous chromosomes- chromosomes that were inherited from different parents (not genetically identical because one comes from egg one comes from sperm) • Sister chromatids- results from DNA replication; each chromosome is genetically identical Meiosis I: • Replicated chromosomes condense and line up o Diploid cell- cell contains a homologous pair (2 sets of chromosomes) • Crossing over occurs o Genetic information gets “shuffled up” o “crossing over”- 40% of the time, in a homologous pair, a chunk of the maternal chromosome will switch places with the paternal chromosomes § Enormous variation • Paired up chromosomes move to equator of cell • Random and independent assortment of homologous chromosomes o Think of each pair as “flipping a coin” • Homologous chromosomes separate • Diploid cellà 2 Haploid cells (NOT genetically identical) • Each chromosome still has 2 sister chromatids • Cytoplasm divides • Result: o 2 haploid cells, genetically different cells § 2 chromatids/chromosomes Meiosis II: • Goal is to separate the sister chromatids • Result: 4 non-identical haploid daughter cells (genetically different gamete cells) Example: If a parent cell has 16 chromosomes (8 homo pairs) and undergoes meiosis, each resulting cell will have how many chromosomes? • Each parent cell has 16 chromosomes • Genetic material is copied (32) • Then genetic material is split into two (16) • Then split again into haploids (8 chromosomes) Meiosis generates enormous variation: • Chromosome pairs align randomly and separate independently • 2^24 (8,388,608) combinations are possible • 8,388,608 possible egg cells * 8,288,608 possible sperm cells o yielding more than 70 trillion genetically unique individuals for one couple (theoretically!) Genetic variation: • crossing over • assortment of homologues • alleles come from two parents Purpose of sexual reproduction: • Variation in genetic makeup of a population o Natural selection acts on this variation Diversity in sexual reproduction is important: • Asexual: all cells are alike but once an ecological disaster happens, it can not adapt and the cells are killed off • Sexual reproduction: through time, these differences accumulate. This way, if the ecological disaster hits this population, there are individuals who are resistant to this disease and survive, so this population continues to live. Haploid gametes (n = 23) Egg cell n n Sperm cell FERTILIZATION 2n Key Haploid (n) Diploid (2n) Fertilizationà Mitosisà Meiosis: fertilization: egg & sperm are put together to become a zygote Diploid zygote divides in the process of mitosis Production of gametes (sex cells) in a multicellular adult- meiosis Differences of Mitosis and Meiosis:
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