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19 Cards in this Set
- Front
- Back
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How is Consanguineous mating represented in pedigrees? What is it a feature of? |
Double line Autosomal recessive |
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Explain autosomal dominant inheritance and features |
Affected individuals are heterozygous for mutation Huntingdon's -microsatelitte – expansion is atriplet repeat. Polyglutamine tract. No male/female bias. Reduced penetrance (36-39) - modifier genes, hormonal/ carcinogensVariable expressivity Co-dominance - two aleleles in heterozygous state |
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Autosomal recessive with example What are features |
Cystic fibrosis - ASO hybridisation Parents of affected children are not affected Compound heterozygous have inherited two different mutation - hereditary breast cancer Skips generations Consanguinity Different mutations in same gene - wide range of effects - CF. CSTB dodecamer minisatellite - cystatin B - inhibits cathepsins. Progressive myoclonus epilepsy when >40, normally 2-3 copies. |
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Explain X-linked recessive inheritance Examples |
Affected males (hemizygous for gene) and females (homozygous) Mostly males affected No male to male transmission Female carrier can show milder features of the condition if the wrong X chromosome is inactivated. Haemophilia A - Pathogenic CNVs intrachromatid recombinationbetween inverted LCR repeatsproducesinversions. Factor VIII gene. DMD |
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Explain X-linked dominant inheritance Example |
No male to male transmission Excess of affected females with milder and variable phenotype because of X-inactivation All daughters of an affected male will be affected but not boys X*Y x XX= X*X, X*X,XY,XY Fragile X Syndrome - autistic,mentalretardation. >200 CGG in 5' untranslated region of FMR1. Methylation of CGG repeat expansion at FMR1 promoter - silencing of FMR1 gene and lack of product. But anticipation and X-inactivation
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Differences from X-linked recessive |
X-linked dominant less common More females - all daughters of males, 50% from female. |
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What is penetrance? |
proportion of individuals carrying a particular variant of a gene (allele or genotype) that also expresses an associated trait (phenotype). Incompletepenetrance ofmutation. |
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What is anticipation? |
As a genetic disorder is passed on to the next generation, the symptoms of the genetic disorder become apparent at an earlier age with each generation Also, increase of severity of symptoms Due to the expansion of trinucleotide repeats with dynamic mutations |
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What is genomic imprinting? |
If the allele inherited from the father is imprinted, it is thereby silenced, and only the allele from the mother is expressed. If the allele from the mother is imprinted, then only the allele from the father is expressed. Rare. Epigenetic process - DNA and histone methylation without altering genetic sequence Epigenetic marks are established in germline of parents and maintained through mitotic cell divisions in the somatic cell |
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What are three types of repetitive disease causing mutations? |
-Copy Number Variants(CNV) -Expansion orcontraction of tandemly repeatedDNA -pathogenic microsatellites (Dynamic mutations) and minisatellites |
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What is Compound heterozygosity? Where is it seen? |
two recessive alleles for the same gene, but with those two alleles being different from each other autosomal recessive lower penetranc - mutations involved are often less deleterious in combination than for a homozygous individual |
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What does a dot in the circle/square mean? |
Obligate carrier - not manifest disease |
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X inactivation
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•RandomX inactivationineach mother cell. Same X is inactivatedin daughter cells •Heterozygousfemalewill bemosaic for the mutantallele in X-linked disorders Transcriptionally inactive structure called heterochromatin. |
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What is genetic heterogeneity? |
Single phenotype or genetic disorder may be caused by any one of a multiple number of alleles or non-allele (locus) mutations |
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What is •Expressivity? |
Variabilityin diseaseseverity fromidentical mutation when allele is penetrant a gene canmodify the expression of a second gene - modifier gene |
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Example of imprinting |
Paternal inheritance of a deletion of this region is associated with Prader-Willi syndrome
Maternal inheritance of the same deletion is associated with Angelman syndrome |
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What % of the genome is repetitive DNA? |
45% |
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How are foetuses represented? Expected signal in southern blot? |
Diamond Faint signal |
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What is the name of no mode of inheritance seen? |
•denovo mutation. |
