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18 Cards in this Set
- Front
- Back
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Nomenclature for Dominant and Recessive Traits
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Dominant Traits
A – mutant allele a – normal allele Recessive Traits A – normal allele a – mutant allele |
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Types of Genetic Disease
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1. Chromosomal
2. Single gene (Mendelian) 3. Multifactorial 4. Teratogenic |
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Mendel’s Laws
1. LAW OF UNIT INHERITANCE 2. LAW OF SEGREGATION 3. LAW OF INDEPENDENT ASSORTMENT |
1. LAW OF UNIT INHERITANCE - Parental characteristics do not blend because there is a unit of inheritance
2. LAW OF SEGREGATION - The two alleles at a particular locus segregate into different gametes 3. LAW OF INDEPENDENT ASSORTMENT - Alleles at different loci assort to gametes independently of each other |
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Features of Autosomal Dominant Inheritance
-Marfan's -Achondroplasia -Neurofibromatosis Type 1 |
-Vertical transmission
-Both sexes affected in 1:1 ratio -Both sexes may transmit the trait -Heterozygotes much more common than homozygotes -May see variable expressivity and variable age of onset -Homozygotes may be more seriously affected than heterozygotes -May be due to new mutation -Gene product is usually a structural (non-enzymatic) protein |
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Features of Autosomal Recessive Inheritance
-Sickle Cell -PKU -Cystic Fibrosis |
-Horizontal transmission within the same sibship or generation
-Both sexes affected in 1:1 ratio -Both sexes may equally transmit the mutant allele -May observe consanguinity -Gene product is usually an enzymatic protein |
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X-Inactivation
-Duchenne Muscular Distrophy -Hemophillia A |
-Allows dosage compensation between males and females for genes on the X chromosome
-In females, early in embryonic life, one of the X chromosomes is inactivated -The process is random and clonal Some genes escape X-inactivation |
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Features of X-Linked Recessive Inheritance
-Vitamin D resistant Rickets |
-Diagonal inheritance – affected males related through females of the maternal line
-Absence of male-to-male transmission -Incidence of trait much higher in males than females -Full expression in hemizygous males -No or mild expression in carrier females due to X-inactivation |
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Features of X-Linked Dominant Inheritance
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-Twice as many females with the disorder as males
-Absence of male-to-male transmission -Males with the disorder transmit it to all daughters and no sons -Females usually have more mild and variable expression due to X-inactivation -Few disorders classified as X-linked dominant |
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Penetrance
-Retinoblastoma -Waardenburg syndrome (deafness) |
-The probability of expression of the phenotype given the genotype
-reduced penetrance = >100% expression of individuals who carry the responsible allele -Term used for dominant conditions |
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Variable Expressivity
-Neurofibromatosis Type 1 -Myotonic dystrophy |
-The extent to which a trait is expressed
-If expression ranges from mild to severe then it is said to have variable expressivity |
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Variable Age of Onset
-Huntington's disease |
variation in the time to observable expression of the trait
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Pleiotrophy
-Marfan's |
multiple phenotypic effects of a single gene
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Locus Heterogeneity
-deafness |
Mutations at two or more different loci result in the same or similar phenotype
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Allelic Heterogeneity
-CF ΔF508/S549R |
Presence of different mutant alleles at the same locus; compound heterozygote
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Sex-Limited
-Auto dom male precocious puberty |
a trait that is autosomally inherited but expressed only in one sex
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Sex-Influenced
-Hemochromatosis |
a trait that is autosomally inherited but expressed differently, in either degree or frequency, in males and females
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Describe MYOTONIC DYSTROPHY
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-Facial weakness
-Cataracts -Progressive muscular weakness -Variable onset -Variable expressivity |
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Describe Marfan Syndrome
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-Tall stature with long limbs
-Narrow facies with high, narrow palate -Dislocated lenses & myopia -Cardiac manifestations, i.e., aortic aneurysm -Variable expressivity -Pleiotropy |
