L7 Single gene inheritance patterns

L7 Single gene inheritance patterns - Inheritance Patterns...

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Unformatted text preview: Inheritance Patterns Single gene 1 Last Time Gametogenesis: sperm and egg production Stages of meiosis Important features New perspectives on Mendel’s Laws Sex linked traits Sex determination Key experiments in X-linked traits 2 Inheritance patterns Molecular basis of single gene phenotypes Dominance can be expressed in as a range, not an absolute Why are dominant disease alleles still around??? Environmental influences Traits influenced by sex Genes with multiple alleles Pleiotropy 3 What does ‘wild type’ actually mean? Wild type genes - sequence or phenotype that occurs most commonly within a population WIKIMEDIA.ORG 4 Mutants Alterations to wild type sequence Tend to be rare, recessive and loss of function mutations WILD TYPE MUTANT 5 Molecular basis of phenotypes 6 Lethal alleles: mutations in essential genes If a loss of function mutation occurs in an essential gene, the organism dies 7 The spectrum of dominance AA Y Y y y Aa aa TT Tt tt COMPLETE DOMINANCE INCOMPLETE DOMINANCE CODOMINANCE 8 Relationships between alleles can be relative Depends on what level of hierarchy we’re examining - organismal, biochemical, molecular 9 http://graphics.jsonline.com/graphics/badger/img/may02/5martin506.jpg http://universe-review.ca/I10-10-polydactyly.jpg http://fastolfe.net/2007/01/16/reynolds-dwarfism Dominant disease-causing alleles 10 Why do disease-causing dominant alleles persist? 1. Variable Expressivity 2. Incomplete Penetrance 3. High Recurrent Mutation Rate 4. Late Onset 11 Variable expressivity Example: Marfan syndrome Long limbs http://graphics8.nytimes.com/images/2007/08/01/health/adam/9611.jpg marfan-association.org.uk/. 12 Incomplete penetrance Example: Polydactyly 13 Age of onset Example: Huntington’s Chorea Individuals who will develop the disease usually have passed on the allele before they know they have the disease 14 High recurrent mutation rate Example: Achondroplasia Almost 85% of cases of achondroplasia are the result of new mutations, not inherited 15 Environmental influences on phenotype Examples: Temperature-sensitive (ts) alleles Dietary influence on PKU Environment Genotype Phenotype 16 Temperature sensitive (ts) alleles seasonal coat color sex determination http://www.bio.usyd.edu.au/Shinelab/research/malejacky.jpg fur pigmentation 17 Dietary influence on PKU PKU diet untreated http://www.skyrunner.com/baby/p_firsttest.jpg http://www.dshs.state.tx.us/newborn/images/PKU_untreated.jpg 18 Norm of reaction Phenotypic range expressed given genotype 19 Sex influenced inheritance Example: Male pattern baldness 20 Sometimes multiple alleles exist for a single locus (gene) COURSES.BIO.PSU.EDU 21 Multiple alleles: rabbit coat color > Chinchilla (cchch, cchcch, cchc) > Himalayan > hch, chc) (c Full coat color (CC Cch, Ccch, Cc) Albino (cc) 22 Pleiotropy TRC.UCDAVIS.EDU/ A single gene can give rise to several phenotypes Phenotype 1 GENE A Phenotype 2 Phenotype 3 23 Summary Molecular basis of single gene phenotypes Dominance can be expressed in as a range, not an absolute Why are dominant disease alleles still around??? Environmental influences Traits influenced by sex Genes with multiple alleles Pleiotropy 24 Ungraded problems Be sure you understand problems S1, S2, S3, S5, S6* Try: C2, C4, C5, C6, C9, C12 25 Next Time Multiple Gene Inheritance Patterns HTTP://WWW.BEDDINGPLANTS.COM.AU/SEASONAL/DOWNLOADS/MOONFACE_PETUNIA_LG.JPG 26 ...
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