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Extensions_of_mendelian_analysis_contd Lecture 5

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Molecular Biology and Genetics
MBG 2040
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Lecture Set 5 Extensions of Mendelian Analysis ContinuedSEXINFLUENCED TRAITSTraits for which both males and females have the genes but the expression of these traits varies from males to females We always use a superscript or subscript on the alleles to indicate we are dealing with sexinfluenced genes Ex pattern baldnessoPattern baldness is a sexinfluenced traitoPattern baldness is commonly seen in men as they ageMaleFemale11BBNormalNormal12BBBaldNormal22B BBaldBald Pattern baldness seems to be a dominant trait in males Pattern baldness seems to be a recessive trait in femalesoMales with pattern baldness could be heterozygous or homozygous for the pattern baldness alleleoFemales must be homozygous for the pattern baldness allele to show the phenotype Often characterized by thinning in the crown area in women oQ aTwo parents who are heterozygous for the pattern baldness allele marry What is the expected phenotypic ratio of their male childrenLecture Set 5 Extensions of Mendelian Analysis Continuedo b What is the expected phenotypic ratio of their female childrenSEXLIMITED TRAITSBoth males and females have these genes but only one sex expresses the trait Ex Milk production in cattle is a sexlimited traitEx Cryptoorchidism is a sexlimited trait undescended testicleoIn dogs cryptoorchidism shows autosomal recessive inheritanceaa females are normalaa males have undescended testesGENETIC ANTICIPATIONGenetic anticipation is a phenomenon whereby the symptoms of a genetic disorder worsen with each generation and an earlier onset is observed with each generation Genetic anticipation is seen in traits controlled by genes that can expandaccordion genes A dynamic mutation is an unstable heritable element where the probability of expression of a mutant phenotype is a function of the number of copies of the mutation These mutations typically short sequences repeated many times give rise to numerous known diseases including the Trinucleotide repeat disorders Trinucleotide repeats found within certain genes can expand from one generation to the next Trinucleotide repeat disordersEx Myotonic DystrophyoMyotonic Dystrophy is a rare autosomal dominant disorderoSymptoms worsen from generation to generationoProblems arise based on CTG repeats
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