Genetic Diseases3.1 x 109 bp In Mitochondria 16,569 bp Gene Coding Sequences (Exon) Non coding Sequences (Intron) Non-gene (Extragenetic) Repetitive DNA Tandem repeats (satellite,
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Tandem repeats (satellite, minisatellite, microsatellite)
Interspersed repeats (SINES, LINES)
Non repetitive DNA
10% 90%
<10% >90% 50% 50%
Terminology Genotype = genetic constitution of an individual Phenotype = observed characteristic Homozygous = identical alleles at a given locus Heterozygous = two different alleles at a given locus Autosomes = any chromosomes other than sex chromosomes Autosomal inheritance = involve any chromosomes other than sex chromosomes Pedigree charts = to illustrate the inheritance
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Terminology Locus = position of DNA sequences, or gene on a chromosome Allele = possible alternative form of a given gene
Marfan syndrome Antoine Marfan, a french pediatrician, 1896 Fibrillin-1 (FBN1) gene mutation on chromosome 15 Fibrillin-1 is an extracellular matrix glycoprotein, secreted by fibroblasts Structural component of microfibrils in the formation of elastic fibers in connective tissue Skeletal abnormality, subluxation of the lens (ectopia lentis), CVS abnormalities (mitral valve prolapse, aortic aneurysm, aortic dissection)
Thalassemia Hemoglobinopathy Hemoglobin (Hb): iron-containing oxygen transport protein in the red blood cells Four globular protein subunits – Heme group containing Fe Two alpha(α) and two beta(β) subunits: [Heterotetramer; α2β2 = Hemoglobin A] Alpha thalassemia: HBA1 and HBA2 (16p13.3) Beta thalassemia: HBB (11p15.5)
Polygenic or multifactorial diseases or complex genetic disorders Somatic cell genetic disorders (neoplasia)
Terminology Karyotype = the chromosome constitution of an individual, normal human karyotype is 46,XY (male) and 46,XX (female) Polyploidy = the number of hapoloid chromosome sets is greater than two (2n), triploidy, tetraploidy Aneuploidy = chromosome number is not an exact multiple of haploid number, monosomies, trisomies Trisomy = three representatives of a given chromosome, trisomy 21 in Down dyndrome Monosomy = one member of a chromosome pair is missing, Turner syndrome (45,X) Translocation = the transfer of one segment of a chromosome to another
Sex chromosome disorders : Klinefelter syndrome (47,XXY) Turner syndrome (45,X)
XXX = female with an extra X chromosome XYY = male with an extra Y chromosome XX male = Y sequences are transferred to the X chromosome, look like male with Klinefelter syndrome
Down’s syndrome facies Simian crease Gap between 1st and 2nd toes CVS : Endocardial cushion defect (Atrioventricular septal defect) most common GI : increase risk of Hirschprung’s diseases
Polygenic or multifactorial diseases or complex genetic disorders Somatic cell genetic disorders (neoplasia)
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Multifactorial Inheritance
Normal human characteristics : Blood pressure, height, finger ridges, and intelligence Congenital malformations : neural tube defects, cleft lip and palate, and congenital heart disease Common disorders of adult life : DM, Hypertension, peptic ulcer, and schizophrenia
Heritability and Environmental factors
Heritability : percentage denoting that the genetic contribution of a given disease
If heritability is high, there is a high correlation in relatives
Environmental factors : can be manipulated to reduce an individual’s susceptibility below than the threshold