02BIS1012013XLinkLect3

Lrodriguez 34 hemophilia a pedigree criss cross

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Unformatted text preview: ession, R.L. Rodriguez 31 Characteristics of X-linked Dominant Traits ­ The trait does not skip generations. ­ Affected males must come from affected mothers. ­ Approximately half of the children of an affected Approximately female are affected. female ­ Affected females come from affected mothers or Affected fathers. fathers. ­ An affected father passes the trait to all his An daughters, but none of the sons. daughters, BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 32 Examples of X-Linked Pedigrees X-Linked Recessive X-Linked Dominant (affected male) X-Linked Dominant (affected female) BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 33 Queen Victoria: a carrier for Hemophilia A BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 34 Hemophilia A Pedigree (Criss-Cross Inheritance BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 35 Hemophilia A (defects exon 14 of Factor VIII) BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 36 Hemophilia A (Recombinant Factor VIII) BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 37 Pedigree Analysis ­ Pedigree of rare Pedigree recessive trait (a). recessive ). Propositus (or proband) is IV.2. Unrelated individuals are assumed to be non-carriers. Note the union of III.5 and III.6. III.6. ­ The proband is the The individual who first draws medical attention to a family . BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 38 Pedigree Analysis ­ The absence of The “crisscross” inheritance and the presence of an affected male and affected female in IV, suggest that this is not a X-linked recessive trait but rather a autosomal recessive trait autosomal (a). The propositus is IV.2. ). Unrelated individuals are assumed to be nonassumed carriers. It is not possible carriers. to assign a complete genotypes to some normal looking individuals. looking BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 39 Typical Genetic Counseling Problem A couple suspects they are carriers for Late Onset TaySachs, an autosomal recessive disease that appears Sachs, between 20 and 30 years of age. The couple have 4 young children and want to know the following: children What is the chance that their children will have the disease? What is the chance that their children will be unaffected What or asymptomatic? What is the chance that an unaffected child will be a What carrier? Tay–Sachs Disease BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 02/12/14 40 Typical Genetic Counseling (Solution) A Parents Gametes Siblings Aa Aa 1/2 (A) 1/2 (a) AA 1/2 (A) X 1/2 (a) = 1/4 or 25% + 1/2 (a) X 1/2 (A) = 1/4 or 25% 1/2 25% 50% 50% 1/2 (A) X 1/2 1/2 (A) (A) = 1/4 or 25% 1/4 A Aa 1/2 (a) 1/2 (A) a AA Aa a aA aa aa ? 1/2 (a) X 1/2 (a) 1/2 = 1/4 or 25% 1/4 Unaffected sibs; 2/3 will be carriers BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 02/12/14 41 This Lecture: Mendel, Genes and Chromosomes ­ Using crosses and statistics, Mendel Using demonstrated that traits (genes) were inherited as either dominant or recessive alleles. as ­ Morgan and coworkers prove that genes were on Morgan chromosomes by showing that the eye color gene is linked to sex determining chromosomes in flies. ­ The "attached X" mutant provides cytological The (visual) evidence supporting the Chromosome Theory of Inheritance. Theory ­ X-linked Inheritance provides insight into sex X-linked determination and well known genetics diseases. determination ­ Basic pedigree analysis can reveal genotype. BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 42...
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