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Chapter 4 Lecture Notes

Chapter 4 Lecture Notes - Pedigree Analysis in Human...

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Unformatted text preview: Pedigree Analysis in Human Genetics Chapter 4 The Inheritance of Human Traits Difficulties: Long generation time Data must be obtained from offspring produced Experimental matings are not possible Limited sample size Pedigree Analysis Pedigree = First step in predicting genetic risk What problems could we have with using a pedigree to predict risk? Autosomal Recessive = Autosomal Dominant = XLinked Dominant = XLinked Recessive = Examples of Patterns of Inheritance YLinked Inheritance = Mitochondrial Inheritance = Pedigree Analysis Building a pedigree: using available information rule out patterns of inheritance inconsistent with data Pedigree Analysis Problems: May not have enough information Some genetic disorders more than one pattern of inheritance Catalogs of Genetic Traits Figure 4.4 Fig. 4.4 Autosomal Recessive Traits What is the pattern of inheritance of these traits? Who gets affected more (males or females)? individuals Can show up more often in related Usually these are rare traits Autosomal recessive Fig. 4.5 Fig. 4.5 Autosomal Recessive Traits Albinism Cystic fibrosis TaySachs disease Others: Galactosemia, PKU, Thalasemia, Sickle cell anemia Cystic Fibrosis Disabling, fatal disorder Affects: sweat glands, mucus glands, glands that make digestive enzymes Fig. 4.6 Gene Basis for Cystic Fibrosis Gene located on chromosome 7 Fig. 4.8 Cystic Fibrosis CFTR Gene CFTR regulates chloride ion flow into/out of the cell Makes fluids thick Fig. 4.9 Sickle Cell Anemia What happens in this disease? Homozygous recessive can be lethal Heterozygotes generally unaffected How is this gene helpful? Autosomal Dominant Traits Who is affected by these traits (genetic makeup)? parent Affected offspring = at least one affected Who is affected more (males or females)? Autosomal Dominant Fig. 4.12 Autosomal Dominant Diseases Marfan syndrome Huntington's disease Achondroplasia Others: Familial Hypercholesterolemia, nailpatella syndrome Marfan Syndrome Affects: skeletal system, eyes, and cardiovascular system Phenotype: tall, thin arms and legs with long, thin fingers and toes Fig. 4.13 Marfan Syndrome Weakened aorta may enlarge and rupture High mutation rate Marfan Syndrome May Affect the Aorta Gene is located on chromosome 15 Fig. 4.14 X and Y Chromosomes How many X chromosomes do we have? Hemizygous = If you are male: where did each of your chromosomes come from? X chromosome needed for viable offspring Transmission of X and Y Chromosomes Fig. 4.16 Xlinked Dominant Traits Affected male: what will be the condition of his daughters and sons Heterozygous females how will offspring be affected? Xlinked Dominant Trait Fig. 4.17 XLinked Recessive Who is affected by these traits? Who is most likely to be affected? Affected males where did the allele(s) come from? Affected daughters where did the allele(s) come from XLinked Recessive Traits Colorblindness Muscular Dystrophy Hemophilia Pedigree for XLinked Recessive Trait Fig. 4.18 Colorblindness Most common form = redgreen blindness 8% male population of US Red blindness red not seen as a distinct color Green blindness green or other colors in not seen yellow Muscular Dystrophy Muscular dystrophy = Forms: autosomal and Xlinked Duchenne muscular dystrophy Xlinked, most common 1/3500 males in U.S. Disease progresses rapidly Duchenne Muscular Dystrophy Gene located at end of X chromosome Stabilizes muscle cells during contraction Several mutations with variation in phenotype Fig 4.22 YLinked Traits Who gets affected? All Ylinked traits are expressed Pedigree for YLinked Trait Fig. 4.24 Variation in Gene Expression Penetrance = Factors: Expressivity = expression changes with age genes interact genes and environment ...
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