UMass Amherst BIOLOGY 283 - Genetics Exam 3 Review (18 pages)

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Genetics Exam 3 Review



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Genetics Exam 3 Review

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Pages:
18
School:
University of Massachusetts Amherst
Course:
Biology 283 - General Genetics
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Genetics Exam 3 Review Ch 8 Centromeric locations on chromosomes P Short arm Q Long arm Metacentric Perfectly centered Submetacentric Slightly off center Acrocentric Q 2x longer than P Telocentric Centromere on top only see Q arm Alterations of chromosome structure 1 The total amount of genetic infor in the chromosome can change a Deficiencies Selections b Duplications 2 The genetic material remains the same but is rearranged a Inversions b Translocations Deficiencies When they have a phenotypic effect usually detrimental Terminal deletion Edge of chromosome is lost single break Interstitial deletion two breaks and reattachment of outer pieces Ex Cri du chat 46 5pDuplications Repetitive sequences can cause misalignment between homologous chromosomes if crossing over occurs nonallelic homologous recombination results Usually don t cause harmful syndromes Duplicated genes can be passed on through families and evolve to have similar but distinct functions Gene family Orthologs Same gene in different species Paralogs Different versions of same gene in same species caused by duplications Both of homologs Copy Number variation Small but significant DNA varies in copy number among members of same species Common 1 10 of genome 1 Schizophrenia 2 Autism 3 Susceptibility to infectious disease 4 Cancer Red Green color Vision May have multiple copies due to mispairing and unequal crossing over makes color blindness more likely Inversions Segment that has been flipped into the opposite orientation 1 Pericentric inversion Centromere lies within inverted region 2 Paracentric inversion Centromere lies outsides inverted region Usually has no effect because all the genes are still there Translocation One segment of one chromosome becomes attached to another Caused by chromosomal breakage and DNA repair or Abnormal Crossovers 1 Reciprocal translocations Two nonhomologous chromosomes exchange genetic material 2 Unbalanced translocations Simple Exchange only occurs in one direction cause phenotypic abnormalities like familial Down Syndrome a Majority of chromosome 21 is attached to chromosome 14 Robertsonian Translocation Ex Familial Down Syndrome Breaks occur at the extreme ends of the short arms of two nonhomologous acrocentric chromosomes Small acentric chromosomes are lost Larger fragments fused to their centromeric regions to form a single chromosomes which is metacentric or submetacentric Meiotic segregation can occur in one of 3 ways 1 Alternate segregation a Chromosomes on opposite sides of the translocation cross segregate into the same cell leads to balanced gametes 2 Adjacent 1 Segregation a Adjacent non homologous chromosomes segregate into the same cell leads to unbalanced gametes 3 Adjacent 2 segregation RARE a Adjacent homologous chromosomes segregate into the same cell leads to unbalanced gametes Chromosome numbers can vary in two main ways Aneuploid Variation in the number of complete sets of chromosome Occurs occasionally in animals frequently in plants Aneuploidy Variation in the number of particular chromosomes within a set Regarded as abnormal conditions Trisomy 13 Patau Mental and physical deficiencies wide variety of defects in organs large triangular nose and early death Trisomy 18 Edward Mental and physical deficiencies facial abnormalities extreme muscle tone early death Trisomy 21 Down Mental deficiencies abnormal pattern of palm creases slanted eyes flattened face short stature Polyploids having an odd number of chromosome sets are usually sterile 1 Seedless fruit 2 Seedless flowers Natural Ways that vary chromosome number 1 Meiotic nondisjunction Produce haploid cells that have too many or too little chromosomes offspring would have abnormal chromosomal composition 2 Mitotic abnormalities One chromosome less cell is nonviable other is already a diploid cell and can participate in fertilization but will yield a triploid offspring 3 Interspecies crosses A much more common mechanism for changes in the number of sets of chromosomes is alloploidy Allotetraploid Contains two complete sets of chromosomes from two different species Species A has 2n 16 chromosomes and species B has 2n 14 How many chromosomes would be found in an allotriploid of these two species 22 or 23 16 7 23 14 8 22 Mitotic Abnormalities 1 Mitotic disjunction a Sister chromatids separate improperly causes trisomic and monosomic daughter cells 2 Chromosome loss a One of the sister chromatids does not migrate to a pole causes normal and monosomic daughter cells Genetics abnormalities that occur after fertilization lead to mosaicism Part of the organism contains cells that are genetically different from other parts Polyploid and allopolyploid plants often exhibit desirable traits for breeders try to make these mutations happen The drug colchicine binds to tubulin and promotes nondisjunction Fragile Sites More susceptible to chromosomal breakage indicates regions of non tightly coiled chromatin Can be linked w lung cancer associated with regions of short tandem DNA sequence repeats Fragile X syndrome Folate sensitive site on X chromosome exhibit FXS more common form of inherited mental retardation Dominant trait Ch 10 Hershey and Chase Study bacteriophage Made up of only DNA and protein They marked DNA phosphorus and Protein sulfur with markers and allowed the virus to infect E Coli the infected cells contained the marked DNA but no marked protein Retroviruses Replicate unusually RNA serves as template for DNA synthesis Complementary synthesis of DNA by RNA dependent DNA polymerase reverse transcriptase Nucleic Acid Structure 1 Nucleotides form the repeating units 2 Nucleotides are linked to form a strand 3 Two strands can interact to form a double helix 4 The double helix folds bends and interacts w proteins resulting in 3 D structures in the form of chromosomes Nucleotides A phosphate group a pentose sugar a nitrogenous base Nucleoside A base and sugar Purines Doubles ring Adenine and Guanine Pyrimidines Single ring Thymine Cytosine and Uracil RNA Bases are always attached to the 1 Carbon on the sugar Phosphate group is always attached to the 5 carbon on the sugar RNA or DNA is determined by if there is an O on the 2 Carbon on the sugar Nucleotides are covalently linked together by phosphodiester bonds connects 5 carbon of one nucleotide of the 3 of another Bonded between sugar and phosphate Triphosphates Serve as precursor molecule during any nucleic acid synthesis Energy Linus Pauling Proposed regions of


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