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Bio 130, 15017
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This 7 page Class Notes was uploaded by Bennett Notetaker on Tuesday April 19, 2016. The Class Notes belongs to Bio 130, 15017 at University at Buffalo taught by James Lafountain in Spring 2016. Since its upload, it has received 385 views.
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Date Created: 04/19/16
Block 4 Bio 130: PowerPoint 14 04/19/2016 ▯ Review of Mutations: Mutations represent departure from the norm (wild type gene) at level of single genes Mutations are based on anomalies in base composition of the mutant gene versus the wild type gene ▯ Genomic Instability: Represents a departure from the norm at the level of chromosomes Gain or loss of the individual chromosomes or fractions of chromosomes Polyploidy, aneuploidy, and chromosome translocations are karyotypes that have genomic instability ▯ Euploid in Humans: The euploid is known as the “true karyotype” Euploid is 46,XX or 46,XY Each autosomes has a homologues partner Homologues are structurally identical and have the same gene content X and Y are semi-homologous ▯ Ploidy: Karyotypic feature determined by the number of sets of chromosomes A set is typically designated “n” o Haploid- one set (n or 1n) o Diploid- two sets (2n) o Triploid- three sets (3n) o Tetraploid- four sets (4n) o *Triploids and greater are considered polyploidy* ▯ Human Triploids: Most common human polyploidy Found in 15% to 18% of miscarriages Most result from dispermy, fertilization of a normal egg with 2 sperm Lethal in live births ▯ Human Tetraploids aka 4n: Found in 5% of miscarriages A result of a normal diploid cell experiencing cytokinesis failure Karyotype is 92,XXYY or 92XXXX Lethal ▯ Aneuploidy in Humans: A karyotype having a chromosome number (ploidy) that is not an exact multiple of the haploid set o (2n + 1 = 47) or (2n – 1 = 45) Aneuploidy is usually attributed to genetic non-disjunction- a defect in the mechanism of chromosome segregation ▯ Down Syndrome, trisomy 21 (47,XX, +21): One in 800 live births Physical, behavioral, mental development is retarded Heart defects Higher-than-normal susceptibility to infections and other health- related conditions Life expectancy lower than normal (50yrs) 95% non-disjunction of those 80% MI and 20% MII Parental origin of non-disjunction is 75% oogenesis and 25% paternal origin The origin of the third chromosome 21 can be either sperm or egg o Egg: 24,X, +2147,XX, +21 o Sperm: 23,X or Y47,XY, +21 o Egg: 23,X47,XX, +21 o Sperm: 24,X or Y, +2147,XY, +21 ▯ Aneuploidy of Human Sex Chromosomes: Turner syndrome (45,X)- 1/10000, lacking functional reproductive tract o Egg: 22, no X(45,X) o Sperm: 23, X(45,X) o Egg: 23,X(45,X) o Sperm: 22, no X(45,X) Klinefelter (47,XXY)- 1/1000, phenotype has female features o Egg: 24,XX(47,XXY) o Sperm: 23,Y(47,XXY o Egg: 23,X(47,XXY) o Sperm: 34, XY(47,XXY) o Note that other forms are possible (XXYY, XXXY, and XXXXY) XYY syndrome (47,XYY)- 1/1000, large stature, psychological, emotional issues o Phenotypic features- 1/1000 Clinically “normal” Large structure: average height 6’2” Possible lower IQ than siblings Possible learning difficulties compared to siblings o Egg: X(47,XYY) o Sperm: YY(47,XYY) ▯ Aneuploidy via non-disjunction: Non-disjunction is an outcome of defective chromosome segregation At meiosis I: secondary spermatocytes or oocytes that are (n+1) and (n-1) At meiosis II: spermatids or eggs that are (n+1) and (n-1) Non-disjunction may also be an outcome of defective mitosis (2n+1) (2n-1) ▯ Nondisjunction is outcome of defective meiosis: Correlates with age of maternal germ line Not necessarily a consequence of failure to disjoin (defective separation and/or segregation) Mechanism(s) behind nondisjunction are not yet understood Candidates include defects in cohesion ▯ Structural alterations within individual chromosomes: Duplication of a segment to make extra copies of a chromosome part Translocation of a segment of a chromosome to another chromosome (genomic instability in cancer cells includes translocations) o Reciprocal interchange of parts between non-homologous chromosomes o May be maternal-origin with a non-homologous chromosome of maternal origin o Maternal origin with non-homologous chromosome of paternal origin o Translocations that appear reproducibly in human karyotypes: Philadelphia chromosome: t (9,22), reciprocal translocation generates a new hybrid gene and chronic myelogenous leukemia (CML) Long q arms of chromosomes 9 and 22 Has both genes as a hybrid gene (BCR/C-ABL) Robertsonian translocation: t (14,21), may yield Down syndrome XX male syndrome: t ((X, Y)+SRY gene Swyer syndrome: t (X, Y)-SRY gene Deletion or loss of chromosome part ▯ Chronic Myelogenous Leukemia: Slow pregression Myelogenous=type of white cells Typically affects older adults Run-down, tired feeling (anemia by crowding out red cells) Weight loss Pale skin Night sweats ▯ Biochemical background regarding CML: New gene (BCR/C-ABL) resulting from translocation causes abnormal while blood cells to make constitutively active tyrosine kinase Tyrosine kinase is a “cascade effector” Actions of tyrosine kinase causes white cells to grow and divide out of control by uncontrollable activation of down stream effectors o C-ABL located at chromosome 9, ABL protein is an effector in a cascade that is normally initiated by mitogen and ends with up-regulation of cell division related genes (slide 51) o BCR gene is located at chromosome 22, BCR is an effector in a cascade that is normally initiated by mitogen and ends with up-regulation of cell division-related genes (slide 52) ▯ Philadelphia chromosome has fused genes making BCR/C-ABL: BCR/ABL is a hybrid protein BCR/ABL protein is an effector that is constitutively active Division-related genes are ALWAYS expressed ▯ Philadelphia Translocation: (46,XX, t9, 22) (46,XY, t9, 22) Spontaneous (not inherited) Factors include age, male, radiation Treatments- o Target tyrosine kinases to block action o Blood stem cell transplant o Interferon therapy (as a biological therapy against diseased white cells) ▯ ~Gleevec is a competitive inhibitor for the ATP binding site on hybrid protein~ ▯ Robertsonian Translocation: Special type of on-reciprocal translocation Centromere regions of two non-homologous acrocentric chromosomes become fused to forma a single centromere q arm of chromosome 21 connects via centromere fusion to q arm of chromosome 14, making a compound chromosome Translocation occurs at the centromere (46,XX,t14,21) and (46,XY,t14,21) In most cases both parents have normal chromosomes In other families the mother is the carrier parent ▯ Isochrome Configuration: Loss of p arm and duplication of q arm Results in an “isochromosome” that has two q arms Resultant is isochromosome may have two centromeres ▯ Four Origins of Down “trisomy 21”: Meiotic nondisjunction in MI or MII (47,XX-XY,+21) Mitotic nondisjunction in early embryogenesis (mosaic 47,XX-XY, +21) Robertsonian translocation (46,XX-XY,t(14q,21q) (3% of total Down children) Isochromosome (46,XX-XY, +21q21q) ▯ ▯