Lecture 32 Genetics - Autusomal Recessive

Lecture 32 Genetics - Autusomal Recessive - Learn the...

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Learn the characteristics of AR inheritance and recurrence risks Learn about carrier/gene frequency Learn about consanguinity and probability of disease Learn about genetic isolates Outline: - Autosomal Recessive Inheritance and disease o Concept o Characteristics o Examples o Gender as a factor - Gene frequency and carrier frequency - Consanguinity - Genetic Isolates and importance - patterns of inheritance: single and complex o single gene: autosomal dominant: expressed even when only one chromosome carries the mutant allele recessive: disease expressed only when both chromosome carry mutant alleles x-linked dominant recessive mitochrondial o complex inheritance - Autoso m al recessive inheritance a nd diseas e o Diseas e exists only in ho mozygotes (or co mpound o Why: one single normal copy is enough to compensate and prevent the disease o How: Inheritance of one mutant allele from each parent to get the disease - Autoso m al recessive (AR) Pedigree o - AR disorders a nd recurrence risks o - Characteristics of AR Inheritance o Both males and females affected. (except sometimes…) o Affected individuals can skip generations o Parents of an affected child are usually asymptomatic carriers of mutant alleles. o Unaffected sibs of affected homozygotes may be carriers. o Recurrence risk for homozygous affected progeny in each subsequent pregnancy is one chance in four (25%). o If incidence of the disorder is rare, consanguineous parentage often seen. - Exam ples of AR disorders o Enzyme deficiencies: e.g., PKU, Tay-Sachs disease o Part of newborn screening in general (PKU) and susceptible populations (Ashkenazi Jews for Tay-Sachs) o Ion Channel defects: e.g., Cystic Fibrosis o Most common AR disorder in Caucasian children o Virtually unknown in Asian populations o Rarer in African-American populations Learn the characteristics of AR inheritance and recurrence risks
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