Chapter 15 - Eukaryotic chromosomes, Mitosis and Meiosis

Chapter 15 - Eukaryotic chromosomes, Mitosis and Meiosis -...

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Click to edit Master subtitle style 4/30/11 EUKARYOTIC CHROMOSOMES, MITOSIS, AND MEIOSIS CHAPTER 15
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4/30/11 Chromosomes contain the genetic material Genes are physically located within the chromosomes Chromosomes are composed of DNA and proteins Eukaryotic chromosomes n Typical chromosome contains a single, linear, double-stranded DNA molecule n DNA must be folded and packaged n Chromatin is the DNA-protein complex
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4/30/11 Compaction DNA wraps itself around histone proteins Nucleosome is a repeating unit of DNA wrapped around an octamer of histone proteins Negative charges of DNA attracted to positive charges of histones Amino terminal tails of histone proteins protrude
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4/30/11 30-nm fiber Nucleosome units are organized into a more compact structure that is 30 nm in diameter Shortens the nucleosome structure another sevenfold Structure has proven difficult to determine because n 30-nm fibers interact with the nuclear matrix n Compacts 30-nm fiber by participating in the formation of radial loop domains n Anchored to nuclear matrix
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4/30/11 Each chromosome - located in discrete non-overlapping chromosome territory Different chromosomes are not substantially intertwined n Compaction is not uniform n Heterochromatin n Highly compacted and transcriptionally inactive n Some localized regions in non- dividing cells n Euchromatin n Less condensed and capable of gene transcription n Most chromosomal regions in non- dividing cells n Chromosomes compact further when the cell is preparing to divide n All euchromatin converted to
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4/30/11 In metaphase chromosomes, highly compacted radial loops remain
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4/30/11 Mitotic cell division A cell divides to produce 2 new cells genetically identical to the original Original called mother, new cells called daughters Involves mitosis and cytokinesis Can be for asexual reproduction or for
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4/30/11 Cytogenetics Field of genetics involving microscopic examination of chromosomes Tightly compacted chromosomes have distinctive shapes and number of chromosomes visible with light microscope
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4/30/11 Eukaryotic chromosomes occur in sets Humans have 23 different types Sex chromosomes are designated X and Y in humans In many species, individual has 2 sets of chromosomes Humans- 23 pairs for 46 total chromosomes n When a species is diploid, members of a pair of chromosomes are called homologues n One of each of the these pairs comes from the mother, the other from the father n Very similar, nearly identical in size and genetic composition n Slight differences provide variation in gene function
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4/30/11 MITOSIS Cell division in eukaryotes requires a replication and sorting process that is more complicated than simple binary fission Eukaryotic cells that are destined to divide progress through a series of 5 phases ( G1, S, G2, M and C) known as n In actively dividing cells, G1, S, and G2, are collectively know as interphase n A cell may remain for long periods of time in the G0
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Chapter 15 - Eukaryotic chromosomes, Mitosis and Meiosis -...

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