Genetic Disorders

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Information about Genetic Disorders

Published on January 12, 2008

Author: Michelino


Slide2:  Molecular Genetics: study of the structure and function of chromosomes and genes Heredity: transmission of characteristics from parents to offspring Trait: two contrasting choices Genotype: genetic makeup of organism (TT, Tt, tt) Phenotype: what is physically observed (tall, short) Heterozygous: two different alleles (Tt); hybrid Homozygous: two identical alleles (TT, tt); purebred Slide3:  Austrian Monk, born in 1822 University of Vienna Job at monastery was to teach science and tend the garden Major study done on characteristics of pea plants Slide4:  Pollination: pollen grains from male part of plant fertilize the egg from the female portion of the plant Self-Pollination: pollen and egg from same plant; all offspring characteristics the same as parent (Pea Plants) Cross- Pollination: pollen and eggs from different plants; offspring characteristics formed from a combination of parental genes Slide5:  Male: Stamen: anther + filament Anther: produces pollen grains Filament: holds up anther Female: Stigma: top of pistil, sticky to catch pollen Style: tube leading from stigma to ovary Ovary: contains ovules Ovules: when fertilized will become seeds Slide6:  Closed petals Always self-pollination Purebred: if allowed to self-pollinate, all offspring identical to parents EX: all short, tall Experiment: Mendel prevented self-pollination by removing stamen and using a paint brush to transfer pollen grains to stigma Results Hybrids: produced by crossing parents with different characteristics Slide7:  Dominant Traits: characteristic that when present is always expressed Recessive Traits: masked by dominant trait; only appears if there are two copies P-Generation: purebred parent generation; produce offspring identical to themselves Ex: Mendel found: tall/tall produced only tall, short/short only short F1- Generation: first filial generation; produced by cross-pollination Ex: Mendel found tall/short produced tall plants F2- Generation: second filial generation; offspring of crossed F1 Ex: tallF1/tallF1 = tall and short plants Slide8:  A diagram to aid in predicting the probability that certain traits will be inherited. Monohybrid Cross: Punnett square involving only one trait (2x2) F2 Generation: Tt x Tt T T t t Genotypic Ratio: 4:0 Tt Phenotypic Ratio: 4:0 tall T t T t Genotypic Ratio: 1:2:1 Phenotypic Ratio: 3:1 Slide9:  Gene: individual factors that do not blend with one another; control traits in living things Allele: each alternative for a gene; genes/chromsomes occur in pairs; Ex: T and t Law of Segregation: Alleles are segregated (separated) during meiosis. Only one allele from parent is present in gamete. Occurs during anaphase when chromatids separate. Law of Independent Assortment: factors for different traits are separated during meiosis; dominant traits are not necessarily inherited together Slide10:  How can you tell if a phenotypically dominant organism is homozygous or heterozygous? Cross with a recessive If homozygous: offspring will all be dominant. If heterozygous: offspring will be both dominant and recessive. Slide12:  Complete Dominance: when one allele totally masks the other allele Dominant trait occurs with TT or Tt, recessive only tt Ex: Tall plants, rolling tongue upwards, crossing hands Ratio when crossing two heterozygous: 3:1 Slide13:  Incomplete Dominance: occurs when two or more alleles influence the phenotype; when heterozygous, results in a third BLENDED phenotype Ex: Red and white flowers = pink Ratio: 1:2:1 Slide14:  Codominance: occurs when both alleles for a gene are expressed in a herterozygous offspring; DO NOT BLEND, both are equally dominant Ex: Roan Horse Ratio: 1:2:1 Slide15:  Recessive Defective Hemoglobin on RBCs Anemia (loss of blood cells) Damage to brain, heart, lungs Primarily in African Americans; 1/10 in US is a carrier Slide16:  Recessive Point mutation stops production of a protein in the lungs and pancreas Prevents cells from transporting Cl- ions out of the cell Lung Congestion Abnormally thick mucus lining in lungs Chronic Bacterial Infections (pneumonia) Treated with antibiotics, lung transplant, and new genetic engineering treatments Slide17:  Recessive Lack of enzyme hexosaminidase A (hex A), which breaks down fatty acids in brain in nervous tissue Symptoms appear at 4-6 months Death by 5 years Found primarily in those descendants of Ashkenazi Jews 1/30 American Jews carry the gene Slide18:  Autosomal- Dominant Lethal Begins around ages 35-45 First symptoms; mild forgetfulness and irritability Lose control over muscles Genetic Marker: short section of DNA that has a close association with a known gene Presence of gene marker can indicate the presence of huntington’s allele People with marker have 90% chance of developing Huntington’s Gene Marker and gene so close on chromosome rarely separated by crossing over during meiosis Slide19:  Dominant Disorder 1/20,000 people Believed to be caused by a mutation in the fibrillin gene on chromosome 15 Connective Tissue defects Dislocation of lens in eye Rupture of aorta (weak vessel walls) Arachnodactyly – “spider fingers” Elongated body, face Pectus Excavatum (caved in chest) Slide20:  Abraham Lincoln? Descendents of Lincoln’s great-great grandfather (8th generation) diagnosed with Marfan’s Lincoln could have had a mild form of Marfan’s Should we test Lincoln’s DNA? Slide21:  Do not contain enzyme phenylalanine hydroxlyase (PAH) that breaks down amino acid phenylalanine into amino acid tyrosine Phenylalanine builds up in brain Toxic to central nervous system (CNS) Mental Retardation Tested at birth PKU – 1/10,000 U.S.  1/50 carry PKU allele Regulated by Strict diet Low protein: no meat, eggs, dairy No Aspartame: sugar substitute sold as Equal or NutraSweet Contains amino acid phenylalanine – 50% Slide23:  Cross that involves two traits; more allele combinations possible; 4x4 Punnett Square Ex: Peas  Green/Yellow & Round/Wrinkled Ratio: 9:3:3:1 Slide24:  3 or more alleles for a single trait EX: ABO blood groups – blood types Characterized by the presence or absence of antigens 4 Types: A, B, AB, o A Blood has A antigen but no B, AB has both, O has neither Represented by I (isoagglutination) Codominant Slide25:  Sex- Influenced: Presence of male or female hormones influences the expression of the trait Males and females with the same genotype will have different phenoypes Ex: baldness; B=baldness, B’=normal hair BB=bald (male/female) B’B’=normal hair (male/female) BB’= bald (male) normal (female) Slide26:  Presence of gene on a sex chromosome (X or y) X chromosome is larger than y  more genes carried on the X X-Linked Genes: genes found on X chromosome Appear mostly in males Only one copy of X; nothing to counteract “bad gene” Females would need two copies to express trait Slide27:  X-linked recessive Cannot distinguish between different colors Most common type is red/green colorblindness Heterozygous females have mosaic retinas in which they have patches of color vision Heterozygous female is considered a carrier Slide28:  X-linked recessive Most Common in males “Bleeder’s Disease” Missing clotting factor Bleeding spontaneously and in joints Queen Victoria: descendents affected with hemophilia Alexei Romanov Slide29:  X-linked recessive Most Common in males 1/3500 Muscle Enlargement Dystrophin Protein that provides support for the cell; without it, cell enlarges and explodes Slide30:  X-linked recessive Most Common in males “Lorenzo’s Oil” Degradation of myelin sheath surrounding nerves (insulation) Current News: Oil not as effective as previously thought Cholesterol lowering drug, Lovastatin seems to work Bone Marrow Transplants work in some cases Lorenzo Odone turned 27 on May 29, 2005 (Still completely paralyzed) Slide31:  Barr Body Only in females Inactivated X chromosome Random whether mom’s or dad’s X Dark staining mass in nucleus Allows for equal genetic expression between males and females (both express 1 X) X-inactivation: EX: Calico Cat Coat color is X-linked recessive Large patches of color (Black or orange) Not in males because they only have 1 X Slide32:  Genomic Imprinting: variation in phenotype expression depending on which parent gave the chromosome Chromosome “remembers” which parent it came from EX: Deletion of Chromosome 15 Prader-Willi: uncontrollable eating, diabetes, mental retardation Deletion of portion of paternal 15 Angleman’s: behavior problems, some mental retardation Deletion of portion of maternal 15 Slide33:  Holandric Traits: genes on the y chromosome; carry genes for male sexual characteristics Absence of these genes causes female development Small arm of y chromosome responsible for individuals that have a sex chromosome combination that does not match their appearance XX males and XY females due to absence or presence of SRY factor Ghengis Khan Mongolian warrior 13th century 8% of men living in region that was once Mongolian empire have same y chromosome Slide34:  mDNA inherited strictly from the mother 600 bp region that is extremely different in unrelated individuals Romanovs: Tsar Nickolas II of Russia murdered during Bolshevik Revolution in 1918 Remains identified by comparing mDNA to maternal descendants Anna Anderson: pretended to be Anastasia Proved false by mDNA Slide35:  Pedigree: family record that shows how a trait is inherited over several generations Shows both recessive and dominant traits First Step in genetic counseling Symbols: Slide38:  Gene Mutation: affects either one nucleotide or one codon Substitution: one nucleotide is replaced with a different nucleotide resulting in a new codon If new codon codes for same amino acid – no effect If new codon codes for a different amino acid or stop codon – incorrect protein Ex: Sickle Cell Anemia Substitution: Adenine replaced by Thymine in a single codon; results in a defective form of hemoglobin Frame-shift Mutation: caused by additions and deletions of one nucleotide; all codons after mutation are grouped incorrectly Mutation at beginning of gene is worse than near the end of gene Slide40:  Germ-Cell: occurs in gametes; only affect offspring Somatic Cell: affects body cells; only affects organism Lethal: causes death; often before birth (miscarriages) Chromosome: changes to part or the whole chromosome; cannot be repaired by enzymes Deletion: loss of a piece or whole chromosome Inversion: segment of chromosome breaks off and reattaches in the reverse order on same chromosome Translocation: piece of chromosome breaks off and reattaches to a nonhomologous chromosome Down’s Syndrome: Trisomy 21; 3rd 21 can translocate to chromosome 13 (young mothers) Duplication: part of chromosome attaches to homologous chromosome giving two copies of gene on that chromosome Nondisjunction: failure of a chromosome to separate from its homologous chromosome during anaphase of meiosis; one gamete receives extra copy of chromosome other gamete does not receive one Slide41:  Karyotype: chromosomes are stained and photographed under the microscope, cut from photo and arranged by size and shape; can detect chromosomal abnormalities Monosomy: a zygote with only 45 chromosomes; one copy of a chromosome Trisomy: three copies of a chromosome; 47 chromosomes total Both result from nondisjunction Slide42:  Trisomy 21 Mild to severe mental retardation Distinct Facial Features Heart Defects Fingerprints – Sworl Most Common Birth Defect – 1/700 births Mother’s Age over 40 – 1/80 Problems during Oogenesis Slide43:  Trisomy of sex chromosomes; XXy male Feminine Characteristics, Infertile George Washington? No Children – Sterile? Dental Problems Height – Very tall for generation Still Inconclusive Slide44:  Monosomy of Sex Chromosomes; XO female Infertile Dwarfism Overweight Some mental retardation Webbed Neck Slide45:  Trisomy 18 Elfin Appearance Low set ears Malformation of many organs – specifically heart/lungs “Blue Babies” due to lack of oxygen 90% die within first 6 months Slide47:  Trisomy 13 Cleft Lip and Palate Polydactyl – more than ten fingers/toes 1/6000 births Most die within first year Slide48:  “Cat’s Cry” Syndrome Deletion of a portion of Chromosome 5 Mental Retardation Slide50:  Invitrofertilization (IVF): “test tube babies” Procedure: Woman treated with fertility drugs to regulate menstrual cycle and develop high quality eggs Eggs collected using a needle Fertilization occurs in a Petri dish Within 72 hours embryos transferred to uterus Multiple births often occur Artificial Insemination: fertilization occurs within uterus (in vivo) Sperm inserted through a catheter passing through the cervix into the uterus Slide51:  High frequency sound waves with computer produce image Locate fetus during amniocentesis and CVS Estimate fetal age, sex, twins 600 disorders can be diagnosed prenatally Spina bifida, heart defects, dwarfism, hydrocephalus (water on brain) Slide54:  Fetal Cells obtained from either amniocentesis or chorionic villi sampling (CVS) Cultured and a karyotype created to diagnose genetic disorders Alphafetoproteins (AFP) levels indicated in sample; different levels signal defects Low AFP levels Down’s Syndrome High AFP levels Spina Bifida: spinal cord not contained within spinal column Twins Slide55:  Genetic Screening: a person with family history for genetic disorders are screened before deciding to have children Karyotype of individual created to check for any chromosomal abnormalities Genetic Counseling: couples at risk for having children with genetic disorder seek medical guidance to determine their chances of having a child with a disorder Punnett Squares Slide56:  Needle removes small amount of amniotic fluid from sac surrounding baby 14th – 16th week Fetal cells and proteins are analyzed Karyotype Slide57:  Through cervix and vagina, remove sample of chorion (tissue between uterus and placenta) Same DNA as baby 8th – 10th week Fast results since cells grow faster Dangerous to fetus Slide58:  Identify embryos that do not carry gene for inherited disease Cystic Fibrosis, sickle cell anemia Reduces the risk diseases are passed on to children Genetic Analysis of one cell from embryo before implantation Biopsied with needle under microscope; doesn’t harm development of healthy fetuses (cells – blastomeres) Only healthy embryos implanted; some are saved for later use DOES NOT ALTER genetic material DOES NOT always occur prior to in vitro PGD for X-Linked: sex determination Only not at risk females are implanted Gender selection and family balancing Check for Huntington’s disease, CF, chromosomal translocation when one parent has a translocation and they cause miscarriages in those babies produced Slide60: (Gregor Mendel) (Pea Plants) (Flower Diagram) (Incomplete Dominance) (Roan horse) (Dihybrid Cross) (Lincoln) (Blood Types) (x-linked inheritance) (romanovs) (Nondisjuntion) (Mutations) (Sickle Cell) (Blood Typing) (Colorblindness Retina) (Y Chromosome) (Hemophilia Punnett Square) (Hemophilia Knee) (Queen Victoria’s Pedigree) (DMD Photo) (Lorenzo Odone) (Barr Body) (Calico Cat) Slide61: (Sickle Cell) (Cystic Fibrosis Chest Scan) (Tay Sachs Tissue Sample) (Marfan’s Diagram) ency/esp_imagepages/2927.htm (Pectus Excavatum) GettysburgAddress.htm (Abraham Lincoln) 11nondisjunction.gif (Nondisjunction) mutations3_rev.shtml (Down’s Syndrome Karyotype) issue7329/twib.shtml (Down’s Syndrome) 18258/ped-karyo2.htm (Klinefelter’s Karyotype) portraits/presidents/ (George Washington) default.html (Turner’s Syndrome Karyotype) 2002/2155/slide17.gif (Turner’s Syndrome) or3/edwardssyndrome/ (Edward’s Karyotype) album11.htm (Patau’s Syndrome) (Patau’s Karyotype) June/DSCN0558.JPG (Polydactyl) ped/topic504.htm (Cri-du-chat karyotype) ../criduchat.cfm (Cri-du-Chat person) kirk/cory/babyscans.html (Ultra Sound) pregnancyepilepsy_index.shtml (UltraSound) Ultrasound-Sept_17-2.jpg (Ultra Sound Image) AMO_whatis.html (Amniocentesis Diagram) 050214/full/050214-6.html (Amniocentesis) health/health-info/do... (Chorionic Villi Sampling) designer-children2.htm (PGD) ivf/pgd.php (PGD) IBhuntingtons.shtml (Huntington’s Inheritance) (3D ultrasound) (Fish cartoon)

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