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Chapter 4 - BB (1)

A dominant allele does not always penetrate into the

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Unformatted text preview: term indicates that a dominant allele does not always “penetrate” into The the phenotype of the individual the The measure of penetrance - at the population level – If 60% of heterozygotes carrying a dominant allele exhibit the trait of If the allele, the trait is 60% penetrant the – In any particular individual, the trait is either penetrant or not Expressivity Expressivity is the degree to which a trait is expressed In the case of polydactyly, the number of digits can vary – A person with several extra digits has – A person with a single extra digit has person – A person does not express at all Environment Environment Environmental conditions may Environmental have a great impact on the phenotype of the individual – Snapdragon flower color vs. Snapdragon vs temperature and degree of sunlight Geneticists - examine a range of conditions norm of reaction of the environmental influence on phenotypic range norm the norm of reaction for eye facet number in genetically identical flies the raised at different temperatures raised Phenylketonuria – Autosomal recessive disorder - humans – a defect in the gene that encodes the enzyme defect – phenylalanine hydroxylase Overdominance Overdominance - the phenomenon in which a heterozygote is more Overdominance vigorous than both of the corresponding homozygotes vigorous – heterozygote advantage Sickle-cell anemia Sickle-cell – Autosomal recessive disorder Autosomal – Affected individuals produce abnormal form of hemoglobin HbA Encodes the normal hemoglobin, hemoglobin A HbS Encodes the abnormal hemoglobin, hemoglobin S HbSHbS individuals- red blood cells that deform into a sickle shape under co...
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