Lec 8 Bio 308
Lec 8 Bio 308 Bio 308
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This 5 page Class Notes was uploaded by Kiara Reyes on Tuesday October 4, 2016. The Class Notes belongs to Bio 308 at Northern Illinois University taught by M. Johns in Summer 2016. Since its upload, it has received 11 views. For similar materials see Genetics in Biology at Northern Illinois University.
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Date Created: 10/04/16
Lecture 8: Mitosis and Meiosis Chromosomes Key features of a Chromosomes -Centromere (spindle attaches) -Telomeres (special structures at ends) -Arms ( bulk of DNA) Chromosomes come in 2 forms, depending on the stages of cells cycle -Monad (form consists of a single chromatid) a single piece of DNA containing a centromere and telomeres at ends -Dyad (form consists of 2 identical chromatids “sister chromatids”) attached together at the centromere Chromosomes are in the dyad from before mitosis and in the monad form after mitosis Dyad form is the result of DNA replication: a single piece of DNA (monad chromosome) replicated to form 2 identical DNA molecules (2 chromatids of the dyad chromosome) Homologues: two members of a pair of chromosome; Diploid organisms have 2 copies of each chromosome from each parents Haploid number (n): each species has characteristics number of chromosomes Ex] Humans have n=23 (pairs of chromosomes) Drosophila has n=4 (pairs of chromosomes) Cell Cycle Cell Cycle: theoretical concept that defines the state of all relative to cell division 4 stages: G1, S, G2, M -(M) Mitosis where cells divides into 2 daughter cells. Chromosomes go from dyad (2 chromatid) form to monad (1 chromatid) form -S=DNA synthesis. Chromosomes monad to dyad -G1= Gap. Cells spends most time; Monad chromosomes -G2= Gap. Dyad chromosomes, cell getting ready for mitosis G1, S, and G2 are collectively called Interphase, time between mitoses Mitosis Mitosis: ordinary cell division among the cells of body -During mitosis the chromosomes are divided evenly, each of the two daughters cells end up with 1 copy of each chromosomes Stages: Prophase, Metaphase, Anaphase, Telophase “Prophase” -chromosomes condense -nuclear envelope disappears -centrioles move to opposite ends of cells -Spindle forms “Metaphase” -chromosomes lined up on cell equator, attached to spindle at centromeres “Anaphase” -centromeres divided where chromosomes are monads -monad chromosomes are pulled to opposite poles by spindles “Telophase” -cytokines: cytoplasm divided into 2 separates cells -chromosomes de-condense -nuclear envelopes re-form -spindle vanishes Meiosis Meiosis: special cell division that converts diploid body cells into haploid gametes (only occurs in specialized cells) Takes 2 cells division, M1 and M2 with no DNA synthesis between “First Meiotic Division (M1)” Main event in prophase of M1 is crossing over (also called recombination) In cross over, homologous chromosomes pair up (synapsis) and exchange segments by breaking and rejoining at identical locations Several cross over per chromosome with random positons and pairs of homologous chromosomes line up together “Second Meiotic Division (M2)” Prophase, the chromosomes condense and spindles forms Gametogenesis in Mammals Gametogenesis: creation of sperm and egg cells from the products of meiosis, through changes in cytoplasm Sperm production is continuous from puberty until death. All 4 meiotic products remodel their cytoplasm and grow long flag to become spermatozoans or sperm cells Gametogenesis in Female Mammals -Meiosis resumes after puberty, under hormonal control -After ovulation, the oocyte finishes meiosis 1 -Meiosis 2 only occurs after fertilization Angiosperm Life Cycle Angiosperm are flowering plants All eukaryotes alternate between a diploid phase and haploid phase Plant Diploid Phase= Sporophyte: large visible plant body Plant Haploid Phase=Gametophyte: lower plants, stage is quite short and small “Angiosperm Gametophytes” Male gametophytes (pollen grain) consists of 3 haploid nuclei. Nuclei are derived from one haploid meiotic product, by mitosis. Two nuclei are “sperm nuclei” and other control the metabolism of pollen gain Female gametophytes (ovule) consists of 8 haploid nuclei. These 8 nuclei are derived from one of the meiotic products “Double Fertilization” All angiosperm undergo double fertilization: major defining characteristic of angiosperms Pollen grain land on stigma of flower. Germinate a long “pollen tube”, which containing the ovule. The 2 sperm nuclei migrate down the pollen tube into the ovule Each ovule has a cell at one that is pollinated by one of the sperm nuclei. Fertilized cell is diploid, and it grows into the embryo and ultimately into sporophyte plant body Pollen gains lands on stigma of flowers, germinates a long “pollen tube”, which contains the ovules. The 2 sperm nuclei migrate down the pollen tube into ovule. “Seed Development” After fertilization, both embryos and endosperm grow and develop into seed. Resting stage containing multicellular embryo and multicellular endosperm surrounded by protective coat
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