Genetics

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Author:
lacey0133
ID:
45209
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Genetics
Updated:
2010-10-26 17:34:04
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pathophysiology
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DNA Genes and chromosomes
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  1. DNA is composed of
    • Deoxyribose: pentose sugar molecule
    • Phosphate molecule
    • Nitrogenous bases: pyrimidines: Cytosine and Thymine, Purines: Adenine and Guanine
  2. Pyrimidines
    Cytosine thymine
  3. Purines
    Adenine and Guanine
  4. Genes
    • Composed of DNA
    • biologic and basic unites of inheritance
    • Portions of chromosome with particular nucleotide sequence: code for proteins
  5. Chromosomes
    • Composed by genes making up the genetic material in the nucleus
    • Functions in transmission of genetic information
  6. # of chromosomes
    • 23 chromosome pairs, 22 homologous pairs of autosomes, 1 pair sex linked
    • 46 chromosomes
  7. Genotype
    • the genetic constitution of an organism
    • XX: female (homologous)
    • XY: male (nonhomologous)
  8. Phenotype
    any observable characteristic or trait of an organism
  9. Mitosis
    • Preproduction and division of somatic (body) cells
    • Chromosomes replicate
    • 46 replicated chromosomes line up on spindle and one verson of each pulled into daughter cells
    • each new cell contains the entire genetic information in 23 pairs of chromosomes
  10. Meiosis
    • Reproductin of gametes (sperm and egg cells)
    • Occurs in the reproductive cells (germ cells) of the ovary or testicle
    • Involves two cell divisions resultion in four haploid cells with one of each chromosome paire
  11. DNA replication
    • copy DNA
    • weak hydrogen bonds are broken "unzipping" the DNA double helix
    • Each chain serves as a template where teh complementary molecules attach and build the new double strand
    • DNA is formed and replicated in the nucleus
  12. Protein Synthesis
    • Occurs in cytoplasm, specifically in ribosomes
    • DNA code is transported from nucleus into the cytoplasm
    • Protein is then formed via transcription and translation
    • Process is mediated by RNA
  13. RNA
    • Ribonucleic Acid
    • Similar to DNA except
    • Sugar molecule (deoxyribose vs ribose)
    • Uracil rather that Thymine as a base
  14. Transcription
    messenger RNA (mRNA) is created and moves from nucleus into cytoplasm
  15. Translation
    Complementary base pairing occurs with mRNA, which specifies the sequence of amino acids via transfer RNA (tRNA); ultimately results in the formation of a polypeptide chain
  16. mitosis unwanted changes
    Genetic errors can change information of the daugter cells through: errors in replication, translocations, deletions, inversion, duplications, and more
  17. Meiosis unwanted changes
    Errors result in germ cells with a potential for genetic diseases: Translocation, deletions, inversions, duplications, and sorting errors such as nondisjuction (failur to seperate)
  18. Mutation
    • any inherited alteration of genetic material
    • May cause disease or be subtle, silent substitutions, that do not change the amino acids
    • rare events: rate of spontaneous mutation is 1/10,000 to 1/10,000,000
  19. base pair substitution
    one base pair replaces another
  20. Frameshift mutation
    insertion of deletion of one or more base pairs of the DNA molecule
  21. Mendelian disorders
    • Single gene disorders
    • Changes in single gene often a sigle codon which results in functional changes in the protein for which it codes
  22. Codon
    a sequence of 3 bases in a strand
  23. Multifactoral or multigenic genetic disorders
    • traits produced by multiple genes
    • changes in many genes that contribute to a disease
    • not considered officially as a strictly genetic disease, as environmental influences affect the expression of the trait
  24. Abberation
    • Deviation from normal
    • chromosomal aberrations are the leading known cause of mental retardation and miscarriage
    • change in # of chromosomes
    • change in shape of chromosomes
    • addition of genetic information to a chromosome
    • deletion of genetic information from a chromosome
  25. aneuploidy
    • an abnormal # of chromosomes (change from 23 pairs)
    • usually the result of nondisjunction
    • to many is better than too few; loss of chromosome material is fatal
  26. Nondisjunction
    • A failure to separate normally during meiosis or mitosis
    • occurs in a variety of ways but the result is the same > an abnormal number of chromosomes in the daughter cells
  27. aneuploidy due to nondisjunction in meiosis
    upon fertilization the resulting cell has either 1 or 3+ copies of the chromosome rather than the standard pair
  28. Aneuploidy due to nondisjunction in mitosis
    results in cells with less than or more than the full complement of chromosmes (often seen in cancer cells)
  29. Autosomal aneupoidy: trisomy 21
    • Down Syndrome: Extra copy of chromosome 21
    • 1/800 to 1/1000 births (risk increases with maternal age)
    • Face: low nasal bridge, epicanthal folds, protruding tongue, low-set ears
    • MSK: hypotonia, short stature
    • Systemic disorders: congenital heart disease, reduced ability to fight resp infections, intestinal stenosis, increase susceptibility to leukemia
  30. hypotonia
    poor muscle tone
  31. other autosomal aneuploidys
    • trisomy 13 or 18: rare occurence, sever retardation, survive a few weeks- a year
    • trisomy 8,9, or 22: exist rarely
    • except for sex chromosomes and chromosome 21, monosomy and trisomy are probably not compatible with life
  32. Sex chromosome aneuploidy
    Many varieties of intersex conditions, now called disorders of sex development
  33. Klinefelter syndrome
    • Disorder of sex development
    • 47 chromosomes (2+ X's Ex:XXY)
    • 1/1000 male births (often not diagnosed until puberty)
    • male appearance but usually sterile
    • abnoral sexual development and feminization: testicular atrophy, infertility, tall, long arms and legs, feminine hair distribution, gynecomastia, high pitched voice, impaired intelligence
    • treatment: testosterone
  34. Turner Syndrome
    • Disorder of sex development
    • 45 chromosomes (monosomy X)
    • 1/5000 female births with high pre/postnatal mortality (increased with paternal age/damaged x)
    • Female phenotype: short stature, webbing of neck, sterility, fibrous ovaries, amenorrhea, wide chest, congenital heart defects
  35. Deletions
    Broken chromosomes and lost DNA (cri du chat short arm of chromosome 5 missing)
  36. Duplications
    addition of genetic material (duplication of chromosome 5 mental retardation but less serious physical defects that deletion)
  37. translocation
    interchange of genetic material between non-homologous chromosomes
  38. inversion:
    When two breaks take place on a chromosome and an inverted reinsertion of the missing fragment takes place
  39. Cri du Chat Syndrome
    • Deletion short arm chromosome 5
    • severe retardation, round face, congenital heart anomalies
    • infant crying resembles a cat
    • some live to adulthood
  40. Autosome
    any chromosome other than the sex chromosome
  41. autosomal dominant trait
    • males and female children are equally affected
    • only need one affected parent
    • if you have gene you have disease (severity (expression) varies)
  42. Marfan syndrome
    • Autosomal dominant
    • a genetic disorder of the connective tissues due to a mutation of a protein
    • mutation of fibrillin 1 gene on chromosome 15
    • characterized by long thin extremeties, reduced vision due to dislocation of the lens, cardiovascular abnormalities (mitral valve prolapse, and aortic dissections), chest deformities
  43. fibrillin 1, marfan fibrillin 1
    • Fibrillin 1: a glycoprotein secreted by fibroblasts provides inmortant scaffolding for deposition of other matrix proteins such as elastin
    • Marfan Fibrillin 1: more susceptible to proteolytic degradation than normal fibrillin, leading to weak connective tissues
  44. Autosomal Recessive Trait
    • Males and females equally affected
    • Parent may but probably dont have (are carriers)
    • expression variable
    • cystic fibrosis, alpha 1 antitrypsin deficiency, phenylketonuria, sickle cell anemia, albinism
  45. albinism
    • autosomal recessive
    • lack pigmentation: hair skin eyes
    • at least 6 different forms of oculocutaneous albinism
    • some are associated with organ defects
    • lack enzyme tyrosinase which catalyzes the formation of dopa from tyrosine. Dopa is the precursor of melanin
    • Risk for sunburn skin cancer impaired vision and photo sensitivity
  46. Cystic Fibrosis
    • Autosomal recessive
    • 70% from one mutation but > 800 mutations identified
    • characterized by: thick tenacious secretions in lung, gi, gu, resp tract infections, meconium ileus, pancreatic failure, infertility
    • now can survive to middle age, commonly with lung transplant
  47. Sex-linked disorders
    • disorders caused by genes located on sex chromosomes
    • X-linked recesssive diseases much more common
    • more males affected, women are generally carriers
    • hemophilia A (factor VIII deficiency)
    • Duchenne muscular dystrophy
  48. Hemophilia A
    • Sex-linked disorders
    • factor VIII deficiency
    • Queen victoria was 1st carrier in bristish royal line
    • about 15-20% of genetic defects aris from spontaneous mutation (cant blame mom)
  49. Duchenne Muscular dystrophy
    • Lack dystrophin (protein that provides the structural integrity for muscle membranes)
    • Results in severe muscle wasting
    • usually survive to mid-twenties
  50. Multifactorial (polygenic) diseases
    • traits produced by several genes acting together
    • not considered a genetic condition in the sense of being produced by a single gene
    • environmental factors influence the expression of the train (height iq)
    • asthma, schizophrenia, adult onset diabetes, hypertension
  51. Environmentally induced congenital disorders (teratogens)
    • any agent that can disrupt the develpment of the embryo or fetus: cause errors by interfering with cell proliferation, migration, or differentiation
    • Congenital disorders can arise if development is affected
    • Nutritional: folic acid
    • Chemicals/drugs: cocaine, fetal ETOH, tetracyclines
    • Infections: viral (chickenpox)
    • Radiation:
  52. Environmentally induced congenital disorders (susceptibility to teratogens)
    • Amount of exposure
    • fetal age when exposed
    • any prior conditions of the mother
    • genetic predisposition of the fetus
  53. prenatal tests
    • ultrasounds
    • pedigree analysis: mapping determine chromosomal location of genes
    • Embryoscopy: allows direct visualization of the embryo as early as the first trimester
    • Chorionic Vilus Sampling: usually 10-12 weeks, the genetic material in chorionic villus cells is the same as that in the babys cells
    • amniocentisis: week 15-20 a test to study amniotic fluid looking for sex of baby, chromosome problems, lung maturity, infection
  54. Fetal alcohol syndrome
    • associated with low socioeconomic status
    • growth retardation, neurologic disorder, malformations of head and face (epicantal folds, flat nasal bridge, small peripheral fissure, railroad track ears, upturned nose, smooth phyltrum, thin upper lip), atrial septal defects
    • mechanisms include maternal fetal hypoxia and excessive free radical production
    • alcohol causes acute and transient collapse of the umbilical cord which could damage the fetus by interrupting its oxygen supply
  55. TORCH
    • Toxoplasmosis, others (hep B, coxsackievirus B, mumps, poliovirus), rubella, Cytomegalovirus, herpes
    • microorganisms cross the placenta and infect the developing fetus
  56. Rubella
    • Risk of infection begins just prior to conception and extends to 20 weeks gestation after which the virus rarely crosses the placenta
    • cataracts, deafness, and heart defects
  57. Toxoplasmosis
    • contracted from ingestion of raw or undercooked meat and more rarely from contact with cat feces
    • risk of congenital toxoplasmosis is somewhat lower if infection occurs during the first trimester than in if in the third.
    • Hypatosplenomegaly, thrombocytopenia, microcephaly, convulsions, fever, and small for gestational age; hydrocephalus; chorioretinitis (rare), feeding difficulties, small areas of hemorrage (petechiae, purpura), jaundice, hearing impairment, small eyes
  58. periods of fetal vulnerability
    • prior to 1 week: teratogens generally either damage so few cells that embryo develops normally or so many cells that spontaneous abortion occurs
    • 3-9 weeks: embryo is very vulnerable to teratogens. 4-5 weeks is peak of susceptibility
    • 3-9 months: susceptibility to error of morphogenisis is sig less, fetal insults after the third month are more likely to result in growth retardation or injury to normally formed organs

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