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733Lecture03 - AIM OF HUMAN MENDELIAN GENETIC ANALYSIS...

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MENDELIAN GENETIC ANALYSIS IN HUMANS AIM OF HUMAN MENDELIAN GENETIC ANALYSIS To determine relationship between: – the phenotype • (disease or “abnormality”) – the individual genotype quote, p. 85: Thompson & Thompson; Genetics in Medicine “Diagnosis of a variable phenotype requires acute clinical observation, and a large part of clinical genetics is concerned with the diagnosis of disorders complicated by variable expressivity” (Thompson & Thompson, Genetics in Medicine; italics added) PHENOTYPE Observable biochemical, cellular, or clinical characteristic – ASSOCIATED WITH THE EXPRESSION OF A GENE • PHENOTYPES MAY BE CONTINUOUS OR DISCRETE “Genes” may not be genes Not necessarily a one-to-one correspondence between: – Mendelian phenotypes, and – DNA coding sequences • modification by other loci • insertions • microdeletions • translocations • etc. HOW IS THE PHENOTYPE DETERMINED G + E = P NATURE + NURTURE = PHENOTYPE GENOTYPE & ENVIRONMENT PHENOTYPE
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(from Lecture 1) HUMAN INHERITANCE Mendelian character – Particular genotype at one locus is both necessary and sufficient for the character to be expressed • Given the normal genetic and environmental background HOW IS THE PHENOTYPE DETERMINED For some traits – genotype is all important • (SINGLE GENE DISEASES) – EXAMPLE: TAY-SACHS DISEASE – EXAMPLE: HUNTINGTON’S DISEASE HOW IS THE PHENOTYPE DETERMINED For some traits – genotype and environment interact • Example: (single gene defects) – PKU • Example: (possible single gene defects) – JUVENILE DIABETES • Example: (polygenic effects) –NEURAL TUBE DEFECTS HOW IS THE PHENOTYPE DETERMINED For some traits – environment may be predominant or only factor involved • Example: –FETAL ALCOHOL SYNDROME
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