Patho CH. 4 - Genes & Genetic Diseases
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pinacolada117 on August 27, 2011
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70 terms
Terms | Definitions |
|---|---|
 DNA structure | 1. Deoxyribose 2. Phosphate molecule 3. 1 of 4 nitrogenous bases |
| Purines | Double ring nitrogenous bases 1. Adenine 2. Guanine |
| Pyrimidines | Single ring nitrogenous bases 1. Thimine 2. Cytosine |
| Nucleotide structure | - A deoxyribose molecule - A phosphate group - A nitrogenous base |
| Pairings of Bases | - Adenine & Thimine (2 H+ bonds) - Guanine & Cytosine (3 H+ bonds) |
| DNA polymerase | -Enzyme that moves along DNA strand to add correct nucleotides - Proofreads to ensure correct pairing -Excises incorrect matches |
| Mutagens | Agents known to increase incidence of mutation -Radiation -Chemicals (ex. nitrogen mustard, alkylating agents, sodium nitrite |
| Cytoplasm | Where does protein synthesis take place? |
| Protein synthesis from nucleus to cytoplasm by: | Transcription & translation |
| How RNA differs from DNA | -Single strand molecule -Uracil instead of thimine (can pair with aenine) |
| What is transcription? | Process where RNA is synthesized from DNA template |
| Transcription process | -mRNA formed base don DNA sequence -RNA polymerase binds to promoter site (site that specifies beginning of gene) -It then exposes DNA strands with open bases -Then it detaches from DNA -mRNA goes from nucleus to cytoplasm |
| Transcription occurs until | -Termination sequence is reached |
| Ribosome | -Site of actual protein synthesis -Equal parts protein and ribosomal RNA (rRNA) -Binds mRNA and tRNA so base pairing can occur |
| 2 types of human cells | 1.Gametes (sperm & egg cells) 2. Somatic cells (all others beside sperm/egg) |
| Somatic cells | -All cells besides sperm & egg cells -23 pairs of chromosomes (diploid) -One part of each pair from mother and father -22 pairs are homologous; 1 is sex chromosome (XX = female, XY= male) |
| Gamete cells | -Sperm & egg cells -23 single chromosomes (Haploids) -Formed from diploid cells by meiosis |
| Chromosome structure | -Short arm = "p" petite -Long arm = "q" -Centromere = where sister chromatids attach |
| Euploidy | When cells have the normal number of chromosomes |
| Polyploidy | When cells have more copies of each chromosome than normal -Triploidy (3 copies of chromosome pairs) -Tetraploidy (4 copies = 92 pairs) |
| Aneuploid cell | Cell that doesn't contain proper multiple of a specific chromosome; either autosomal or sex cells -Trisomy: 3 copies of a chromosomes (not lethal) -Monosomy: only one copy of a diploid cell (lethal) |
| Viable autosomal trisomies | -13th chromosome -18th chromosome -21st chromosome (Down's) |
| Down's syndrome | Trisomy of the 21st chromosome |
| Down's Syndrome characteristics | -Low nasal bridge, epicanthal folds -Flat, low-set ears -Protruding tongue -Poor muscle tone (hypotonia) |
| Down's Syndrome effects | -Congenital heart defects -Reduced ability to fight respiratory infections -Susceptibility to leukemia -Alzheimer-like by age 40 -20% die before age 10 |
| Trisomy X | -Most common sex chromosome aneuploidy -Females, have 3 X's -Sterility, menstrual irregularity, retardation possible -Symptoms severity increased with # of X's |
| 45X (Turner's Syndrome) | -Single X chromosome in gamete (no X or Y) -Females only (lack of Y chromosome0 |
| Turner's Syndrome characteristics | -Short -Webbing of the neck -Widely spaced nipples -Coarctation (narrowing) or aorta -Sparse body hair -Pedal edema in newborns -Reduced carrying angle of the elbow) |
| Treatment for those with Turner's syndrome | -Estrogen to promote secondary sex characteristics and reduce osteoporosis -Human growth hormone |
| Klinefelter's syndrome (47 XXY karyotype) | -At least 2 XXs, and a Y (male appearing) -Maternal nondisjunction of X, increases with maternal age -Male, but sterile and may appear feminine -Moderate mental impairment -Degree of physical/mental impairment increases with each added X |
| XYY Karyotype | - Affects males - Taller than average - 10 to 15 point less on IQ - Suggested predisposition to behavioral disorder |
| Clastogens | Increase incidence/severity of chromosome breakage -Ionizing radiation -Viral infections -Chemicals |
| Tyes of Chromosome Structure Abnormalities | 1.Deletions 2.Duplications 3.Translocations 4.Inversion |
| Deletion abnormality | -Caused by broken chromosomes and loss of DNA -ex. Cri du Chat |
| Cri du Chat | -Deletion abnormality - deletion of part of chromosome 5 -Low birthweight -Severe mental retardation -Small head (microcephaly) -Cat-like cry |
| Duplication abnormality | Causes less effects that deletion abnormality |
| Inversion abnormality | -Portion of chromosome broken, taken out -Reinserted in inverted order -"Balanced" since no loss of genetic material |
| Effects of Inversion abnormalities | -Often none -"position effects" from neighboring DNA -Mostly affects offspring of affected (cause deletion or duplication) |
| Translocation anormalities | Interchanging of genetic material between nonhomologous chromosomes i.e. Robertsonian translocation |
| Robertsonian Translocations | -Long arms of 2 nonhomologous fuse = 1 chromosome -Chromosome 13, 14, 15, 21, 22 (nonimportant) -Effect seen in offspring with duplications or deletions (21 fused, cause extra 21st =Down's) |
| Reciprocal translocation | -Break takes place in 2 diff chromosomes -Material is exchanged -Gametes can be normal, translocate, or have deletions/duplications |
| Fragile Site Abnormalities | -Areas of chromosome that develop distinct breaks or gaps -No relation to disease, or known cause -Fragile X syndrome |
| Fragile X Syndrome | -Located on long arm of X chromosome -Uncommon since male may not express traits (as is normal with most X-chromosome abnormalities) -mental retardation |
| Locus | Position along the chromosome that a gene occupies |
| Homozygous | When the two genes at a locus are identical (one from each parent) |
| Heterozygous | When the two genes from parents at a given locus are different |
| Genotype | The composition of genes at a given locus |
| Phenotype | The outward appearance of a person with a given genotype (affected by environment) |
| Dominant allele | *The allele whose effects are observable *Denoted by capital letter (Aa or AA) |
| Recessive allele | *The allele whose effects are hidden *Denoted by lowercase letter *To be expressed must be homozygous (aa) |
| Gene carrier | -Individual who carries the recessive gene, but phenotypically does not display attributes -Can be passed to future offspring |
| Mendel's Principle of Segregation | Homologous genes separate from each other during reproduction, and each reproductive cell carries only of of the genes |
| Single-gene Diseases' 4 Major Modes of Inheritance | 1. Autosomal dominant 2. Autosomal recessive 3. X-linked dominant 4. X-linked recessive |
| When is amniocentesis performed? | 16 weeks gestation |
| When is chorionic villus sampling performed? | 10 weeks gestation |
| Amount of risk of prenatal diagnosing of chromosomal abnormalities | Amniocentesis = 0.5% risk losing fetus Chorionic villus sampling = % risk |
| Proband | -First person in the family diagnosed, or seen Male = Propositus Female = Proposita |
| Autosomal Dominant Disorders | -Rare -Males & females equally as likely to inherit -No skipping generations (if child has, one parent must have) -Affected heterozygous people transmit to half of offspring |
| Penetrance | Percentage of persons with a genotype that also exhibit the phenotype |
| Chromosome 13 | "Tumor-suppressor gene" - protein regulates cell cycle |
| Types of Autosomal | -Retinoblastoma -Achrondroplascia -Huntington's disease -Type 1 neurofibromatosis (Recklinghausen disease) |
| Expressivity | Extent of which phenotype is expresses i.e. Recklinghausen disease |
| Von Recklinghausen disease | -Variable expressivity -Range from dark skin spots to numerous malignant fibromas, scoliosis, seizures, HTN, learning disabilites |
| Factors influencing expressivity? | -Genes at other loci (modifier genes) -Environmental factors -Mutations at a locus |
| Autosomal Recessive Disorders | -Rare -Must be homozygous to express disease -Increased incidence in incest -Approx 1/4 of offspring in carrier parents will be affected |
| Cystic FIbrosis | -Autosomal recessive -Defective chloride transport -> salt imbalance -> thick secretions/mucous -Pancreas and lungs mostly affected |
| X-linked Inheritance | -Mostly on X chromosomes, and mostly recessive -Females can by homozygous diesase or normal, or heterozygous -Males who carry recessive X will show traits (Y doesn't hide) |
| Common Recessive Disorders | -Hemophilia (X-linked) -Cystic Fibrosis -Sickle Cell Disease -Duchenne muscular deficiency (lacks dystrophin) (X-linked) |
| Hemophlia A | Factor VIII deficiency |
| Hemophilia B | Factor IX deficiency |
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