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Week 1 Genetics

by: Emma Notetaker

Week 1 Genetics CELL 2050

Marketplace > Tulane University > CELL > CELL 2050 > Week 1 Genetics
Emma Notetaker
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About this Document

Week 1 of notes
Dr. Meadows
Class Notes




Popular in Genetics

Popular in CELL

This 5 page Class Notes was uploaded by Emma Notetaker on Saturday September 3, 2016. The Class Notes belongs to CELL 2050 at Tulane University taught by Dr. Meadows in Fall 2016. Since its upload, it has received 19 views. For similar materials see Genetics in CELL at Tulane University.


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Date Created: 09/03/16
Tuesday, August 30, 2016 Week 1 Chapter 2 • prokaryote: • cell wall • unicellular domains: eubacteria abd archaebacteria • • no nucleus • 1-10 micrometers • one circular DNA molecule, loosely associated • DNA without histones in eubacteria • some histones in archaebacteria no organelles • • eukaryote • unicellular and multicellular • membrane-bound organelles • nucleus • DNA associated with histones to form tight chromosomes viruses • • neither prokaryotic or eukaryotic • outer viral protein coat surrounds nucleic acid - contains DNA and RNA • prokaryotic cell reproduction - binary fission • simple division - separation of replicated circular chromosome • origin of replication - signals replication high rate of replication • • prokaryotes have one chromosome, and as it replicates the origins move to opposite sides • origins anchored to opposite sides of cells that start to split • new cells (2) have identical copies of original chromosomes • eukaryotic cell replication • eukaryotic chromosomes: homologous pair (humans have 23 pairs of chromosomes, 46 total) • • diploids carry 2 sets of chromosomes - 2 sets of genetic info • haploids carry one set • alleles: sites containing genes • chromosome structure • centromere: attachment point for spindle microtubules kinetochores form - bind to microtubules and attach sister chromatids • • telomeres: tips of a linear chromosome, chromosomal stability • stable end • prevents ends from touching each other • 4 telomeres on pair of sister chromatids • origins of replication: where DNA synthesis begins sometimes chromosome is ONE chromatid - one DNA molecule • • sister chromatids stuck together at the centromere (still considered one chromosome as long as chromatids attached) • 2 DNA molecules • cell cycle: passage of genetic info from a parent cell to daughter cell 1 Tuesday, August 30, 2016 • mainly takes place in somatic cells (non-reproductive cells) • interphase: extended period between cell division DNA synthesis and replication • • nuclear membrane is PRESENT in interphase • chromosomes are relaxed • G1: growth • proteins for cell division are made • G0: non dividing phase G1/S checkpoint: regulated decision point • • after this, now committed to division • S: DNA synthesis/duplication • G2: biochemical preparation for cell division • G2/M checkpoint: only passed is DNA completely replicated and undamaged • M phase: mitosis: separation of sister chromatids • • cytokinesis: cytoplasm separates • phase check points are key transition points • important in cancer - cancer disrupts check points • centrosomes give way to spindles • spindles made up of tubulin subunits mitosis: • • prophase • chromosomes condense - can start to see individual chromosomes • 4 chromosomes (2 pairs of homologous) • 8 DNA molecules (8 chromatids) • each chromosome has 2 chromatids • mitotic spindle forms between centrosomes • prometaphase • nuclear membrane disintegrating • chromosomes vert apparent • spindle microtubules attached to chromatids • metaphase • chromosomes line up on metaphase plate • attached at the centromere to the centrosome • anaphase • sister chromatids separate and move toward opposite poles • 8 chromosomes (sisters separated) • 8 DNA molecules (8 chromatids) • telophase • chromosomes at spindle poles • nuclear membrane re-forms • chromosomes relax - can’t see as well • each new cell has 4 chromosomes and 4 DNA molecules • genetic consequences of mitosis • 2 cells that care genetical equal to each other and mother cell • new cells have full complement of chromosomes • each new cell has 1/2 the cytoplasm and organelle content of the original parent • sexual reproduction and genetic variation • meiosis: production of haploid gametes 2 Tuesday, August 30, 2016 • fertilization: fusion of haploid gametes • genetic variation: consequences of meiosis meiosis: • • interphase: DNA synthesis and chromosome replication • meiosis I: reduction division • start with 2n = 4 chromosomes • separation of homologous pairs • reduction of chromosome number by half phases: • • prophase I: • middle prophase I: chromosomes continue to condense and spindle forms • late prophase I: homologous chromosomes PAIR (unlike mitosis) • crossing over (aka chiasmata): segments of one sister go to another - generates variation in gametes (during late prophase I) synapsis: close pairing of homologous chromosomes • • tetrad: closely associated 4-sister chromatids of 2 homologous chromosomes • metaphase I: random alignment of homologous pairs of chromosomes on metaphase plate • in mitosis, no pairing • anaphase I: spindles connect to kinetochores of centromeres • • separation of homologous chromosome pairs to opposite poles • random distribution of chromosomes into 2 newly divided cells • generates variation • at end of anaphase, haploid system (because homologous chromosomes separated) • telophase I: • chromosomes arrive at spindle poles • cytoplasm divides • haploid cell • interkinesis • meiosis II: equational division - ends with 4 haploid cells • separation of sister chromatids • prophase II: chromosomes re-condense • spindles attach • metaphase II: individual chromosomes line up along plate • anaphase II: sister chromatids move to opposite poles • telophase II: chromosomes arrive at the spindle poles, cytoplasm divides • 4 single chromatids • consequences of meiosis: • 4 cells from original cell • chromosome number in each cell is reduced by 1/2 • new cells haploid • new cells are genetically different from each other and parents • crossing over • random separation of homologous chromosomes • genetic variation via crossing over • one chromosome possesses A and B alleles while other has a and b • DNA replication in the S phase produces identical sister chromatids 3 Tuesday, August 30, 2016 during crossing over in prophase I, segments of nonvoter chromatids are exchanged • • after meiosis I and II, each of the resulting cells carries unique combination of alleles • genetic variation via random separation of homologous chromosomes • cells have 3 homologous pairs of chromosomes • maternal: lm, llm, lllm paternal: lp, llp, lllp • • 4 possible ways for these to be combined in interphase I Event Mitosis Meiosis I Meiosis II Cell Division yes yes yes Chromosome no yes no reproduction genetic variation no yes no crossing over no yes no random dist. of no yes no maternal and paternal chromosomes metaphase individual chromosomes homologous pairs line individual chromosomes line up up line up anaphase chromatids separate homologous chromatids separate chromosomes separate separation of chromatids occurs in meiosis II, NOT meiosis I • • separation of sister chromatids and homologous chromosomes • cohesin: protein holding chromatids together • key to bx of chromosomes in mitosis and meiosis • shugoshin: protects cohesin at centromere from being broken down • mitosis: • sister kinetochores orient towards different poles and cohesin keeps sisters together • breakdown of cohesion all chromatids to separate • meiosis: cohesin along arms hold homologous pairs together at chiasmata • • cohesin along arm breaks form, allowing homologs to separate (need to keep sister chromatids intact) • shugoshin keeps kinetochores together while allowing homologs to be pulled apart • at anaphase II, shugoshin is degraded so sisters can come apart meiosis in animals • • spermatogenesis - male gamete production • spermatogonia in testes can undergo repeated mitosis to keep diploid • OR spermatogonium enters prophase I to become primary spermatocyte • each spermatocyte competes meiosis I to make 2 secondary spermatocytes • these go through meiosis II to make 2 haploid spermatids (become sperm) • oogenesis - female gamete production • oogonia enters prophase to become primary oocyte • oocytes go through meiosis I to make large secondary oocyte and smaller polar body 4 Tuesday, August 30, 2016 • secondary oocyte complete meiosis II to make ovum and second polar body (polar bodies disintegrate) • meiosis in plants s • • s • 5


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