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Genetics Wk 1 Notes

by: Anna Ballard

Genetics Wk 1 Notes Bisc 336

Anna Ballard
GPA 3.33
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About this Document

These notes cover what we went over in class the first week.
Ryan Garrick
Class Notes




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This 6 page Class Notes was uploaded by Anna Ballard on Monday October 17, 2016. The Class Notes belongs to Bisc 336 at University of Mississippi taught by Ryan Garrick in Fall 2016. Since its upload, it has received 5 views. For similar materials see Genetics in Biology at University of Mississippi.


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Date Created: 10/17/16
*** For Weds: read first ½ of Ch. 2 and for Fri: read second ½ **** Lecture 2 8/24 Mitosis occurs when organisms are constantly reproducing  Which of the following best describes what a genotype actually is?  ­ it is the combination of alleles at a gene (other options:)   ­ it can either be dominant or recessive ­ makes up chromosomes and genomes – loose view ­ what is passed form parents to offspring – fundamental unit of inheritance is the chromosome Hierarchical Terms (largest –> smallest) Genome – all the genetic info in an organism* Karyotype – number of chromosomes; 2n=46 or n=23 Chromosomes – basic genetic units passed to offspring via gametes Gene – DNA region that codes fora  particular protein**/trait Allele – variant of a gene Genotype – particular combo of 2 alleles of a gene, in an individual ** rRNA and tRNA aren’t proteins, but are products of genes  * we only need a complete haploid (n) set of chromosomes to have every gene represented  Cell Structure and Genetic Function  Nucleus (=eukaryote) – houses DNA  Organelles  – mitochondria, ER, centriole, chloroplast Cytoplasm – colloidal matrix  Cytoskeleton – lattice of tubules and filaments In the Nucleus…. Chromatin • loosely/uncoiled DNA that is unattached from histone  • can see when cells are not dividing  Chromosomes • super condensed DNA that you can only see right before mitosis and meiosis start; otherwise  they are more loosely packed  Nucleolus • rRNA is made here • subunits of ribosomes are initially built here  In the Cytoplasm… • Know Rough and Smooth Endoplasmic Reticulum (SER and RER) • Mitochondria – Powerhouse of cell – cellular respiration • Variable amounts  • Maternally inherited; contains their own haploid chromosomes • their chromosomes live outside of the nucleus  • no heterozygous or homozygous copies of genes because they are haploid • Chloroplasts – (plants, algae, protozoa) involved in photosynthesis • Not in all cells  • Also have their own haploid chromosomes, maternally (flowering plants) or paternally  inherited (angiosperms) • Centrioles – organize the spindle fibers ­ involved in stretching the spindle fibers during mitosis and meiosis  spindle fibers move chromosomes when needed  Chromosome Lengths and Shapes • Centromeres are involved in constriction  •  constricti n • arms of Chromsomes (DNA that may or may not be transcribed or translated)  • metacentric – centromere in middle  • sub­metacentric – long arm when centromere is off center • acrocenttric   • telocentric – when centromere is all the way at top    • FIG 2­3 (2.2) Homologous Chromosomes  • Individuals in a species all contain the same number of chromosomes  ­ except some types of cockroaches  • Occur in pairs • Maternal and paternal parent donate one  • All have same size, morphology, and gene arrays • Sex similar may not look alike or act alike but they do act as homologs • The total number of chromsomes equals the diploid karyotype (2n) Karyotype • Humans: ­ diploid (2n) = 46 ­ haploid (n) = 23    • X and Y are not homologous, but they are paired together Transfer of genetic Material  MITOSIS • Genetically similar across generations of cells • Start with diploid cells and end with diploid cells  • replacing skin cells, growing, replacing hair cells • Point of mitosis = GROWTH Mitosis and the Cell Cycle  …from the end of cell division, to beginning of the next… Regular Function:  • G1, Gap • Cell performing normal function  • Blood cells carrying O2, etc.  • GO  • on path towards dividing via mitosis; not all cells enter • non dividing cells; withdrawn from the cycle heading towards duplication  • S, Synthesis  • where DNA replication takes place • G2, Gap • similar to G1 – cell is still performing normally BUT form in which chromosomes exist has  been altered Mitotic Division:  • Prophase, Metaphase, Anaphase, Telophase • PMAT DNA Molecules, Chromosomes, and Chromatids •  Homologous chromosomes   • centromere in same place and genes in same place on each chromatid • one inherited from ma the other from pa  • big A allele and little a allele – same gene but two different alleles – heterozygous  individual  • here, chromosome = chromatid (1 molecule) •  Homologous Chromosomes after S­phase duplication    • identical copy of each chromosome attached at the chromosome’s centromere  • Now a chromosome is composed of sister chromatids (2 molecules) Mitosis: Prophase • Centrioles migrate to opposite ends (poles) and lay down/organize the microtubules and  spindle fibers • Nuclear envelope breaks  • Chromosomes are now visible sister chromatids • Genetically identical  Mitosis: Metaphase • chromosomes move to the middle and align How to pull apart sisters?  up or out  Mitosis: Anaphase • sister chromatids are pulled apart at the centromere • the sister chromatids move to opposite poles • the separated sisters will now become the daughter cells’ chromosomes   ­ all daughter cells will have identical chromosomes  Mitosis: Telophase • cytoplasm begins to divide to separate the new daughter cells • Chromosomes de­condense and return to chromatin  • nuclear envelope appears • spindle fibers disappear  FIG. 2­7 Lecture 3 8/26 Mitosis: recap 1. Starts with a diploid cell (2n =4) ­ homologous chromosomes – same site, centromere placement, and genes 2. Prophase ­ main events: chromosomes condense, nuclear envelope degenerates, chromosomes move to  opposite sides and lay down spindle fibers 3. Metaphase –  ­ Move to middle 4. Anaphase and Telophase  ­ Cytokinesis  ­  2 new diploid daughter cells that are genetically identical Transfer of genetic Material  Meiosis:  • Genetically similar across generations of organisms  • Diploid –> haploid  ­ How to pass genetic material from one generation to next (from parent to offspring) ­ fusing ½ of each parent DNA allows them to reform to create that next generation’s genetic  makeup Meiosis and Sexual Reproduction •  one DNA replication  • 2 cell divisions  ­ PMAT I and PMAT II  ­ in P I, we have reciprocal genetic exchange between homolog chromosomes  ­ those that form pairs because same size, centromere placement, and genes ­ pair up in meiosis and exchange portions of chromosomes arms  ­ reciprocal exchange – both give each other parts of their DNA  • Genetic exchange aka Crossing over ­ “Gene swap” to create brand new set of genes • genetic variability – combinations of alleles on homologous chromosomes in each zygote  ­ Not every individual is the same – allows for slight advantages to continue being passed  through generations  Meiosis I: Prophase I • Chromosomes were replicated during interphase and are now pretty visible • Homologous chromosomes are now paired/synapsed together <— big difference in meiosis v.  mitosis  ­ physical contact between a chromatid of one chromosome with the chromatid of another  allows for arms to undergo reciprocal exchange (crossing over • 4 chromatids per pair of chromosomes (2X2) Meiosis I: Metaphase I ­ ALWAYS alignment  • Reductional division –> 1st division starts  • Chromosomes move to middle and align  ­ chromosomes still stuck tigether even though crossing over has already occurred   • positioning and placement is random Meiosis I: Anaphase I • Tetrads (sister chromatids) are pulled apart to each pole • these sister chromatids have previously been modified by crossing over  ­ random mix of maternal and paternal genetic material in each chromatid  • the chromatid that did not participate in crossing over is still unmodified  • no longer have chromosomes existing as homologs – on way to making haploid daughter  cells  Meiosis I: Telophase I • reductional division ends  • each chromosome set gets its own nuclear envelope ­ cytoplasm begins to pinch  • short interphase with no DNA replication Meiosis II: Prophase II • begins with the 2 daughter cells that Meiosis I created  ­ chromosomes condense, centrioles move to opposite pole, spindle fibers laid down  ­ no pairing of homologous chromosomes…. no homologs in haploid cells –> no crossing over  • Chromosomes in are already duplicated because they are a pair of sister chromatids Meiosis II: metaphase II • Equational division – 2nd division starts • chromosomes line up in middle ­ again, whichever chromatid ends up on top or bottom is completely random  Meiosis II: Anaphase II • Dyads pulled apart taking one chromatid to each pole ­ random mix of genetic material in each chromatid • each chromosome is a haploid set of the whole genome Meiosis II: Telophase II • Equational division ends • cytokinesis and reformation of the nuclear membrane • end product: 4 haploid gametes  ­ each gamete has a completely different genetic makeup due to the crossing over and  divisions  VIEW FIG 2­10 IN BOOK What is unique to prophase I of meiosis I?  ­ homologous chromosomes pair up ­ crossing over occurs Mitosis v. Meiosis  ­ ctd. next week :) 


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