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Biology 120: Genetic and Molecular Biology

by: Jamisha Evans

Biology 120: Genetic and Molecular Biology BIO 120

Marketplace > Western Kentucky University > Biology > BIO 120 > Biology 120 Genetic and Molecular Biology
Jamisha Evans
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These notes consist of lectures for section 4. This the full study guide but the full study guide
Sahi, Shivendra
Study Guide
Bio, 120, genetic, and, Molecular, Biology
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This 8 page Study Guide was uploaded by Jamisha Evans on Saturday April 30, 2016. The Study Guide belongs to BIO 120 at Western Kentucky University taught by Sahi, Shivendra in Winter 2016. Since its upload, it has received 28 views. For similar materials see BIOL CONC CELLS METAB GENETICS in Biology at Western Kentucky University.


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Date Created: 04/30/16
Biology 120 Study Guide (Genetic and Molecular Biology) Chapter 11 (Sexual reproduction and meiosis)  An overview of meiosis  Meiosis reduces chromosome number by half which is why it is called reduction division  Just before meiosis begins, each chromosome in the diploid (2n) parent cell is replicated  After replication, each chromosome consists of identical sister chromatids attached at the centromere.  Meiosis consists of two cell divisions (meiosis I and meiosis II)  Meiosis I • Diploid parent cell produces two haploid daughter cells ♦ Homologs in each chromosome pair separate and go to different daughter cells • Although the daughter cells are haploid (n) each chromosome still consist of two identical sister chromatids • No replication (S phase) after meiosis I (between meiosis I and II)  Meiosis II • The sister chromatid of each chromosome separate and go to different daughter cells • Meiosis II is similar to meiosis II ♦ The four haploid daughter cells produced by meiosis II also have one of each type of chromosome, but now the chromosomes are replicated • Remember: there is no replication between meiosis I and meiosis II. Replication only occurs before meiosis I during Interphase.  In meiosis chromosomes are reduced from 2n to n (diploid to haploid)  In animals, the diploid daughter cells that comes from the haploid original cell, becomes gametes through a process called gametogenesis.  Fertilization  Fertilization results in a diploid zygote  When two haploid gametes fuse during fertilization, a full complement of chromosomes is restored. • The cell that results from fertilization is diploid (zygote 2n)  Each diploid individual receives a haploid chromosome set from both its mother (maternal chromosomes) and its father (paternal chromosomes)  Phases of meiosis  Interphase- DNA replication/synthesis  Meiosis I: separation of homologous chromosomes • Prophase I • Metaphase I • Anaphase I • Telophase I  Meiosis II: separation of sister chromatids (like mitosis) • Prophase II • Metaphase II • Anaphase II • Telophase II ***Same names just different roman murals (I and II) ***  Phases of Meiosis in detail  Interphase: Chromosomes in parent cell at an expanded (non-visible) state and from sister chromatids.  Meiosis 1 • Early Prophase I: Chromosomes become visible, nuclear envelope disappears and spindle apparatus forms. The two homologous chromosomes pair (synapsis). • Late Prophase I: Sister chromatids cross over and exchange genetic information. Spindle apparatus attaches to the centromere. • Metaphase I: Chromosome are aligned at equatorial plate by the spindle apparatus • Anaphase I: homologs separate and move to opposite side of cell • Telophase and cytokinesis: spindle apparatus disappears and nuclear envelope reappears. Chromosomes move to opposite sides of the cell and then the cell divides. ** Begins with one 2n; Diploid (parent cell) and Ends with two n; Haploid (daughter cells)  Meiosis II • During Meiosis II, practically the same processes occurs as the process in Meiosis I except, that there are two cells and each cell has only one set of chromosomes. ** Begins with two n; Haploid (daughter cells) and Ends with four n; Haploid (daughter cells)  Crossing over  Occurs only during Prophase I and contact is maintained until Anaphase I.  At each point where crossing over occurs, sister chromatids get physically broken at the same point ad attached to each other.  Results in exchange of genetic information between homologous chromosomes which results in recombinant chromosomes (combination of traits that differ from those found in parents.)  Can occur at many locations of the synapsed homologs  Clarification: during crossing over, non-sister chromatids of the homologues chromosomes cross over and attach to each other.  Remember that sister chromatids are either of the two chromatids formedby replication of a single chromosome. Notice that the sister chromatids are crossing over each other and produce gametes with a different genetic makeup than their parents.  Chiasmata: site of crossing over  Crossing over allows the offspring produced to be genetically different from parents instead of a clone. This is we may greatly resemble our parents but we don’t look exactly like them.  Errors in Meiosis  Failures during meiosis will produce games with the incorrect number of chromosomes. ♦ Nondisjunction: failure of chromosomes to move to opposite pols during meiosis I or II.  Produces gametes with less or more number or chromosomes.  Aneuploid gametes: Gametes with improper number of chromosomes. • Can lead to miscarriages, or offspring disabilities (Down syndrome, Turners syndrome, etc.) ____________________________________________________________________________________ Chapter 12 (Patterns of Inheritance) NMT= Non-Mendelian Trait  Gregor Mendel’s experiment system  19 century monk  Studied heredity  Heredity: transmission of traits from parents to their offspring.  Trait: a characteristic of an individual  Studied dichotomous traits and how they are passed on to their offspring.  2 possible alleles for each trait  The combination one has ( 1 from om, 1 from dad) is called genotype (genetic makeup)(ex: Aa.. etc)  Physical make-up is called phenotype (ex: Brown hair)  Homozygous: 2 matching alleles  Heterozygous: 2 different ales (non-matching) EXAMPLE: Homozygous: aa or AA Heterozygous: Aa  Gregor sought to answer specific questions  Why do offspring resemble their parents  How does transmission of traits occur  Two hypothesis were formulated to try to answer these questions • Blending inheritance : parental traits blend and offspring have intermediate traits • Inheritance of acquired characteristics: modified parental traits passed on to offspring  First model organism in genetics: Garden pea plants  Genetics: branch of biology that focusses on inheritance of traits  Mendel chose garden pea plant as model organism to study genetics because  Easy to grow  Short reproductive cycle  Produces large number of seeds  Mating’s are easy to control  Traits are easily recognizable  How did Mendel arrange mating  Self- fertilization: pollinate self (pea plants can do this)  Mendel prevented the peas from fertilizing themselves by removing the male reproductive organs (contains pollen) for each flower. He used the pollen to fertilize the female reproductive organs of flower on different plants. This process is called cross fertilization.  What traits did Mendel study?  Seven easily recognizable traits (he observed the phenotypes) • Pod shape • Pod color • Seed color • Seed shape • Flower and pod position • Stem length  Mendel worked with pure lines (homozygous )which produced identical offspring when self pollinated  Mendel’s experimental method  3 stages • Produce true breeding strains for each trait • Cross fertilize true breeding strains • Allow hybrid offspring to self-fertilize and count number of offspring showing each form of the trait.  Monohybrid crosses • Cross that studies only 2 variations of a single trait (EXAMPLE: seed shape; wrinkled or smooth • In every monohybrid cross he got a 3:1 ratio after the F2 generation. 3 dominant and 1 recessive  F1 generation (first filial generation) • Mendel crossed 2 homozygous breeding strains (RR and rr) (parent generation) • The results: Each offspring was heterozygous dominant (Rr and Rr) (F1 generation)  F2 generation ( Second filial generation) • Offspring from first filial generation were used to create the F2 generation (Rr and Rr) • The results: The phenotypic ratio: 3 round: 1 wrinkled The genotypic ratio: 1 homozygous dominant: 2 heterozygous dominant: 1 homozygous recessive (RR, Rr,Rr and rr)  Mendel’s conclusion from his experiment • The plants did not show intermediate traits. The traits were distinct.  Dihybrid crosses • Cross that studies two separate traits in a single cross • True breeding lines for two traits ♦ RRYY (round and yellow) x rryy (wrinkled and green) • F1 generation shows the dominant phenotypes for each trait (Seed shape; Round, Seed color; Yellow)  F1 generation • RRYY and RRYY were crossed (parent generation) • The results: RrYy and RrYy (F1 generation)  F2 generation • RrYy and RrYy from F1 generation crossed • The results: RRYY, Rryy, rrYy, rryy Phenotypic ratio: 9:3:3:1 Genotypic ratio: 1:1:1:1  Genes, alleles and genotypes  Hereditary determinates for a trait are now called genes  Each individual has two versions of each gene called alleles.  The different alleles are responsible for the variation in the traits that Mendel studied.  Alleles are an individual’s genotype (allelic makeup). The genotype majorly affects the phenotype (physical makeup)  Alleles don’t blend.  The presence of alleles do not mean guarantee expression • Rr: In this case little “r” is shown but not expressed this is a dominant genotype because the dominant trait is expressed. • In order for a genotype to be recessive both alleles have to be present ( little “r”; rr)  Principles of segregation  During gamete formation two alleles for a gene segregate and are rejoined at random. One from each parent.  Mendel developed the principle of segregation  Pedigree charts  Used to track the inheritance patterns in families.  Incomplete dominance: heterozygote intermediate between 2 homozygotes (EX: pink flowers(offspring) from white and red flowers(parents)) (NMT)  Codominance: heterozygote shows some aspect of the phenotypes of both homozygotes (EX: type AB blood; A and B are codominant) (NMT)  Epistasis: offspring doesn’t have an alleles from parents (R.A Emerson crossed 2 white variants of corn; result was 9 purple corn and 7 white corn (NMT)  Extensions to Mendel  Mendel’s model of inheritance assumes that each trait is controlled by a single gene  Each gene has only two alleles  There is a clear dominant recessive relationship between alleles.  Most genes do not follow this criteria  Polygenic inheritance: Multiple genes are involved in controlling the phenotype of a trait. These traits show a continuous variation (EX: Eye color, Human height) (NMT)  Pleiotropy: An allele that has more than one effect on the phenotype (EX: diseases like sickle cell; multiple symptoms can be traced back to one defective allele) (NMT)  Multiple alleles :May be more than 2 alleles for a gen in a population (EX: ABO types in humans (3 alleles) ) (NMT) ________________________________________________________________________ ______ Chapter 14: The genetic material (Review Nucleic acids Ch.3)  Fredrick Griffith  Studied streptococcus pneumonia, a pathogenic bacterium causing pneumonia  S strain: causes pneumonia  R strain: does not cause pneumonia  He injected live S strain, live R strain, heat killed S strain, and heat-killed S+R strain into a mouse. Only the live S strain, and heat-killed S+R strain killed the mouse. This concluded that DNA is genetic material and not protein.  Chargaff  Amount of Adenine=amount of thymine  Amount of cytosine=amount of guanine  Rosalind Franklin  Identified the 3D structure of DNA with X-ray diffraction studies.  Discovered DNA is helical  Watson and crick  Used evidence form Chargaff and Franklin  Created the helical structure of DNA  DNA double helix  Antiparallel  Complementarity of bases  A forms 2 hydrogen bonds to T  C forms 3 hydrogen bonds to G • To remember this, think of how C is the third letter in the alphabet (3 H bonds) , and remember it pairs with G. then remember that A to T has one bond less.  Semiconservative  Combination of daughter and parent genetic material on one DNA double helix.  Determined by Meselson and Stahl  DNA replication  Requires…  Something to copy (template)  Something to do copying (enzyme)  Building blocks to make the copy (deoxyribonucleotide subunits)  Steps in DNA replication  Initiation: replication begins  Elongation: new strands of DNA synthesized by DNA polymerase  Termination: replication stops  Key information about DNA replication  DNA polymerase (III) is the key replicating enzyme • Adds new bases to 3’ end of existing strands • Can only synthesize in 5’ to 3’ (limitation) • Requires help of RNA primer which is removed one replication is complete  Helicase: uses energy form ATP to unwind DNA  Topoisomerase: prevent supercoiling  DNA gyrase (type of Topoisomerase)  DNA replication is semidiscontinuous  This is because the leading strand is synthesized continuously while the lagging strand is synthesized discontinuously • Okazaki fragments on lagging strand which are connected by RNA primer and made by DNA polymerase III. The RNA primer later Removed by DNA polymerase I and replaced with DNA fragments • Okazaki fragments are complementary to the lagging strand template • DNA polymerase I is like the “proof reader” which makes sure there were no mistakes made.  Eukaryotic DNA replication  More complicated than prokaryotic replication because • There is a large amount of DNA in multiple chromosomes • Linear structure  Similar enzymology • Requires new enzymatic activity for dealing with ends only  Multiple origins of replication for each chromosome  Initiation requires more factors to assemble both helicase and primase complexes onto the template then load the DNA polymerase with its sliding clamp unit.  Telomeres • Specialized structures found on the ends of eukaryotic chromosomes (protects ends of chromosomes) • Limitation: unable to replicate lagging strand  DNA repair  2 types • Specific repair: targets single kind of lesion in DNA and repairs only that damage ♦ Photo repair: repair damage caused by UV light • Nonspecific: repairs multiple kinds of lesions in DNA ♦ Excision repair: damaged region is removed and replaced by DNA synthesis. Undamaged strand is used as template ________________________________________________________________________ ______ Chapter 15: Gens and how they work  Central dogma  DNA to RNA to protein  DNA: information storage  mRNA: information carrier  Proteins: active cell machinery  DNA to mRNA (transcription; which occurs in the nucleus)  mRNA to protein (translation ;which occurs in the cytoplasm)  Exceptions to central dogma  Sometimes info flows in the opposite direction- from RNA back to DNA  Reverse transcriptase is used  Francois Jacob and Jacques Monod  Proposed that RNA molecules act as a link between genes  Genetic code  Specifies relationship between sequence of nucleotide bases in mRNA and the corresponding sequence of amino acids in a protein  Transcription and translation in eukaryotes  Transcription and translation are separated. mRNA are synthesized in the nucleus and then transported to the cytoplasm for translation by ribosomes. *** To help you study, take the practices quizzes on McGraw Hill at the end of the chapters included in the study guide (Dr. Sahi class)***


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