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Pedigrees

Pedigrees. Spinal Muscular Atrophy. Severe muscle weakness from birth Loss of motor neurons in the spinal cord. Evaluating Mode of Inheritance. Autosomal Dominant?. Evaluating Mode of Inheritance. Autosomal Recessive?. Fred’s Pedigree. Get to Know Your Classmate.

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Pedigrees

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  1. Pedigrees

  2. Spinal Muscular Atrophy • Severe muscle weakness from birth • Loss of motor neurons in the spinal cord

  3. Evaluating Mode of Inheritance Autosomal Dominant?

  4. Evaluating Mode of Inheritance Autosomal Recessive?

  5. Fred’s Pedigree

  6. Get to Know Your Classmate • Pair up (preferably) with someone you do not know • Pick a trait or disease found in your family or you partner’s family • Draw a pedigree depicting the inheritance of the trait/disease • Try to determine the mode of inheritance

  7. Elizabeth Joe Mildred Bob Elizabeth Mom Doug Stuart Joey Jimmy Jerry Jeffrey Dad Marion Norm Blondeness in Professor Morrissette’s Family Vicki DAM Billy Johnny Roger Zoey Savannah Jasmine

  8. Variations to Mendel’s Laws Extensions and Exceptions

  9. Alterations to Mendel’s Ratios • In these cases, genotypic ratio is as Mendel predicted but phenotypic ratio is altered • Lethal allele combinations • Multiple alleles • Different dominance relationships • Epistasis • Penetrance and expressivity • Pleiotropy • Genetic heterogeneity • Phenocopies

  10. Lethal Allele Combinations

  11. Multiple Alleles • Give a range of phenotypes • Each of us has 2 alleles for any given gene • 1 from mom and 1 from dad • There can be many different alleles for a gene • Different alleles are formed by mutations

  12. Example of Multiple Alleles -PKU • Phenylketonuria (PKU) • Enzyme that breaks down phenylalanine is deficient • Phenylalanine accumulates • There are hundreds of possible alleles • Allelic combinations give rise to different phenotypes • Severe mental retardation • Moderate PKU • Mild PKU • Asymptomatic PKU

  13. Different Dominance Relationship –Incomplete dominance • The heterozygous phenotype is intermediate between the homozygous dominant and the homozygous recessive • Blended phenotype

  14. Different Dominance Relationship –codominance • Phenotypes of both alleles are expressed

  15. Codominance –Blood Type

  16. Codominance –Blood Type

  17. Epistasis • One gene affects the expression of another • Example: If a dog has the hairless gene, the genes that affect hair color will not be expressed

  18. Penetrance and Expressivity • Describe degrees of inheritance • Due to multifactorial inheritance • Expression of a gene is influenced by other genes and by environment • Penetrance =all-or-none expression of a gene • 100% of the people who inherit mutant amyloid precursor protein (mAPP) develop Alzheimer disease so mAPP is 100% penetrant • Expressivity =severity of gene expression • Polydactyly has variable expressivity • Some have an extra toe and others have an extra toe and an extra finger.

  19. Pleiotropy • Gene affects several functions • Phenotype is varied • Example: Porphyria variegata

  20. BBrr bbRR BbRr Genetic Heterogeneity • Different genes produce the same phenotype • Example: • Hearing loss may be due to one of 132 different genes that follow autosomal recessive inheritance B, b =gene for hearing loss type 1 R, r =gene for hearing loss type 2 deaf deaf NOT deaf

  21. Phenocopy • An environmentally caused trait that appears to be inherited • Example: Phocomelia is a rare genetic disorder whose effects are mimicked by the teratogen, thalidomide • Example: AIDs transmission from mother to offspring

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