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35 Cards in this Set
- Front
- Back
how many generation pedegree do you want
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3
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Autosomal Dominant Inheritance
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Heterozygotes express the trait
Vertical pattern of transmission from one generation to the next Transmitted by both sexes Offspring are at 50% risk Structural genes are often involved New mutations are common |
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Phenotypic Variability
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Penetrance
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Incomplete penetrance (def.)
- give example |
a trait that is not expressed in the phenotype of a gene carrier
e.g.,Breast cancer occurs in about 70% of BRCA1 gene mutation carriers -Other genes or environmental factors influence gene expression in these traits. |
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Complete penetrance (def.)
- give example |
a genetic trait that is expressed in the phenotype
-Achondroplasia and neurofibromatosis are highly penetrant mutations |
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Variable expression
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a genetic mutation associated with more than one phenotype
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Autosomal Recessive Inheritance
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Homozygotes express the trait
Horizontal pattern of transmission within a sibship. Transmitted by both sexes Offspring of carrier parents are at 25% risk Functional genes are often involved Ex. Sickle cell disease Consanguinity is more common |
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X-linked Recessive Inheritance
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Hemizygotes (46,XY) are affected; heterozygotes (46,XX) are carriers
When lethal, transmitted by females only - ex. Duchenne Muscular Dystrophy When not lethal, transmitted by both sexes - ex. Color blindness Sons of carrier mothers at 50% risk; sons of affected fathers at no risk |
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Anticipation
e.g., |
The phenotype becomes more severe or evident at a younger age of onset with each successive generation
Ex. The triple repeat mutation can expand with each generation in Myotonic dystrophy. Ex. The premutation for Fragile X in a normal transmitting male expands during female meiosis in his unaffected daughter to a full mutation in her affected son. |
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Parent of Origin effect
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The phenotype varies depending on which parent transmits the abnormal allele
Methylation patterns differ in male and female meiosis: some genes are active only when inherited from one parent (imprinting) Ex. Only the maternal copy of the Angelman syndrome gene is active; the paternal gene is inactive. In utero factors can affect severity Ex. Congenital myotonic dystorphy |
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Polygenic traits
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many genes each make a small contribution to the phenotype
Ex. Intelligence, height |
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Multifactorial traits
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Few genes make a major contribution to the phenotype in a permissive environment
Ex. Spina Bifida, MTHFR and folate deficiency |
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Mosaicism
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A mutation affects only some cells in the body with a variable phenotype
Ex. Gonadal mosaicism in an unaffected parent causes more than one affected child with osteogenesis imperfecta type II, a lethal autosomal dominant trait |
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Chromosomal translocations
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Ex. Down syndrome due to a familial translocation
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Maternal inheritance
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Ex. Mitochondrial genome is cytoplasmic so mitochondrial defects are passed down in the egg cytoplasm from the mother to all of her children
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genetic heterogenity
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mutations in different genes can cause same disease
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genotype/phenotype correlations
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different mutations in same gene can cause different syndromes
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carrier frequency
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prevolence of an altered disease gene in a given population
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founder effect
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high frequency of a specific gene mutation in a population founded by a small ancestral group
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Comparative Genomic Hybridization (CGH) to Metaphase Chromosomes
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Genome scanning technique use for scanning to search for chromosome aberrations
Generally been used to examine chromosome structure in cancer |
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Microarray CGH
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Whole genome hybridization
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polymorphism
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dna sequence changes that do not alter protein function
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mutation
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change in normal base pair sequence
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disease associated mutations
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DNA sequence changes that alter protein function
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wildtype
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non mutant gene
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point mutation
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change in single base pair
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missense mutation
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changes to a codon for another amino acid (can be harmful or neutral)
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nonsense mutation
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change from an amino acid mutation to a stop codon, producing a shortened protein
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frameshift mutations
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insertion or deletion of base pairs, producing a stop codon downstream and usually a shortened protein
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splice site mutation
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a change that results in alterned mRNA sequence
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DNA electrophoresis
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dna loaded into wells and fragments are separated by size and charge
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linkage analysis
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looks for pattern of DNA markers near gene of interest that segregate with disease. Requires DNA analysis of multiple family members
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alelle specific ogliotide (ASO) hybridization
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1)amplify dna
2)add radio labeled normal DNA probes 3)add known mutant dna probes 4) compare (heterozygous, homozygous) |
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PCR
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1) isolate & denature DNA
2)anneal and extend primers 3)repeat as necessary 4)amplify segmenta |
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single strand conformational polymorphism
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1)dna is denatured into single strands
2)single strands fold; shape is altered by mutations 3)mobility of mutant and normal strands differ in gel |