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Chapter 2 Notes

by: Christina Dawson

Chapter 2 Notes ZOL 141

Christina Dawson
GPA 3.5

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Everything about DNA, Cells and Cell Divison.
Introductory Human Genetics
t. mueller
Class Notes
25 ?




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This 7 page Class Notes was uploaded by Christina Dawson on Friday December 11, 2015. The Class Notes belongs to ZOL 141 at Michigan State University taught by t. mueller in Fall 2015. Since its upload, it has received 14 views. For similar materials see Introductory Human Genetics in Animal Science and Zoology at Michigan State University.


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Date Created: 12/11/15
Chapter 2: DNA, Cells and Cell Division  Trait: An observable property of an organism. (Blue eyes)  Gene: Fundamental unit of heredity.  Genome: Set of DNA sequences carried by an individual. Macromolecules  Carbohydrates  Lipids  Proteins  Nucleic Acids: Made of Nucleotides  Nucleotide: Basic building block of DNA and RNA  Consists of three components:  Phosphate  Sugar  Base  Polynucleotides: Linking the nucleotides together to form chains.  Polynucleotide Polarity:  Phosphate at the 5’ end  OH group at the 3’ end  DNA (Deoxyribonucleic Acid): Carrier of Genetic info, found in all living  organisms.  Composed of two strands and forms a double helix  Strands run in opposite directions  Antiparallel  Sugar and phosphate on the outside  Bases on the inside  Genetic info is stored in the sequence  Needs to be self­replicating  Needs to be able to mutate (by changing bases)  Four different nucleotides: A, C, G, T  Base pairing is specific  A and G: Purines  C, T, U: Pyrimidines   RNA (Ribonucleic Acid):  mRNA – messenger RNA  tRNA – transfer RNA  rRNA – ribosomal RNA Base Pairing  A pairs with T: two hydrogen bonds  C pairs with G: three hydrogen bonds  DNA sequence in the two strands is complementary  5’­ATCGGA­3’  3’­TAGCCT­5’  Chargaff Rules:  Amount of A = amount of T  Amount of G = amount of C  Amount of purines = amount of pyrimidines Chemical Interactions  Covalent Bond (Single and double bonds): Chemical bond in which electrons  are shared within a molecule.  Hydrogen Bond: Weak chemical bond between a hydrogen and an  electronegative atom. DNA Replication  Semiconservative  Each strand serves as a template to make a new strand  Each new DNA molecule contains one old and one newly synthesized strand  Replication depends on complementary base pairing  5’ to 3’  DNA replication works only in one direction  New nucleotides are always added to the 3’ end (OH group)  New strand: 5’  Template strand: 3’  3’ OH group binds to the 5’ phosphate of the incoming nucleotide  Two phosphates are removed  Phosphate ions are released  Leading Strand: Synthesized continuously  Lagging Strand: Synthesized discontinuously DNA replication enzymes  Helicase: Unwinds DNA double helix  DNA polymerase: Adds nucleotides to the 3’ end of new DNA strand Chromosomes  Threadlike structure in the nucleus  Linear end­to­end arrangement of DNA  Carry genetic info  Define structure and function of each cell  Humans have 46 chromosomes in a somatic cell (2n=46)  23 pairs (n=23)  44 autosomes (22 pairs)  2 sex chromosomes: Males XY, Females XX  Chromatin: DNA and protein components, visible as clumps or threads  Tightly packed into nucleus  One chromatid = one DNA molecule  Homologous Chromosomes: Pair of chromosomes carrying identical gene loci  One from mom, one from dad  Before replication  One chromosome = one chromatid  After Replication  One chromosome = two chromatids (sister chromatids) The Cell  Basic unit of structure and function in all organisms  Differ in size, shape, function and life cycle  Several different substructures  Function of a cell is under genetic control  Organelles: Cytoplasmic structures with a specialized function  Cell Cycle: Sequence from one cell division to the next  Interphase (G1, S and G2)  G1 (Gap 1): Growth, organelles, membranes and ribosomes are made,  cell increases in size.  Takes several hours  Chromosome: 1 chromatid  S (Synthesis): DNA is synthesized, chromosomes are duplicated  Takes several hours  Chromosome: Two sister chromatids  G2 (Gap 2): Preparation for cell division  Shorter than G1 and S  Chromosome: Two sister Chromatids   Mitosis: Produces two genetically identical daughter cells  Cell needs to divide to survive: growth development and repair  Interphase  Prophase  Cell: Diploid (4 chromosomes)  Metaphase  Chromosomes line up at equator  Anaphase  Chromosomes: consist of one chromatid  Telophase  Cytokinesis: Cytoplasmic cell division  Cells which constantly divide: Bone marrow and skin cells  Cells that do not normally divide: Cardiac muscle cells  Hayflick Limit: Cells can divide about 50 times  Adult cells: 10­30 times  Embryonic stem cells: unlimited  Progeria  1 in 4 million newborns  Mutation in gene LMNA, responsible for shape of nucleus  Affects cell division; cells die prematurely  Affected individuals die by age 13 from a heart attack or stroke  Werner Syndrome  1 in 200,000 live births  Mutation in WRN gene  Rapid aging, no growth spurt in puberty  Roberts Syndrome  Problem with splitting of centromeres, chromosomes don’t line up properly  Symptoms: Short arms and legs, facial abnormalities, deformations, mental  impairment  Very rare (150 individuals known) Meiosis  Cell division which will reduce the number of chromosomes by half  Takes place in germ cells to form gametes (sperm and egg)  Diploid cells will become haploid  Two successful cell divisions: One cell produces four cells  Male: One cell produces four gametes  Female: one functional oocyte and two or three polar bodies  Meiosis I: reduces chromosome number to haploid  Chromosomes replicate during interphase and consist of two sister  chromatids  Prophase I: Homologous chromosomes start to pair  Metaphase I: Pairs of homologous chromosome line up at the equator  Anaphase I: Paired homologous chromosomes separate and pulled to  opposite ends of the cell  Telophase I: Two cells: Haploid  Meiosis II: separates sister chromatids  Prophase II  Metaphase II  Anaphase II  Telophase II: Four gametes: Haploid  Each chromosome consists of one chromatid Diploid vs Haploid  Somatic (normal human cell)  46 chromosomes  Diploid, 2n   Two chromosome sets: one from dad and one from mom  Represents each chromosome twice as a member of a homologous pair  Gamete:   23 chromosomes (no pairs)  Haploid, n  One chromosome set  Represented only once Random Assortment  Random Assortment during Metaphase I homologous chromosome alignment  Allele: One variant of a gene  Different allele can result in a different phenotype  Genes may have many different alleles, but individuals can only have two  One allele is inherited from the father, one from the mother Crossing Over  Crossing over of non­sister chromatids  Physical exchange of chromosome segments  New combinations of mom’s and dad’s alleles Spermatogenesis: Begins at Puberty  Spermatogonia: Divide by mitosis to produce spermatocytes   Spermatocytes: Undergo meiosis to form spermatids (haploid)  Spermatids: Undergo structural changes to become functional sperm Oogenesis: Begins during Embryogenesis  Oogonia: Divide by mitosis to form primary oocytes  Primary oocytes: Undergo meiosis to form Secondary oocytes (haploid)  Secondary oocyte: Produced by the first meiotic division  Unequal division of the cytoplasm: One larger functional gamete (ovum), two or three smaller polar bodies  Ootid: Haploid cell formed by meiotic division of secondary oocyte  Ovum: The haploid cell produced by meiosis that becomes a  functional gamete (egg)


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