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Types of Inheritance

Types of Inheritance. Complete dominance One allele completely masks the other Incomplete dominance One allele doesn’t completely mask the other – result is somewhere in-between Codominance Neither allele completely masks the other – result is a little of each Multiple alleles

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Types of Inheritance

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  1. Types of Inheritance • Complete dominance • One allele completely masks the other • Incomplete dominance • One allele doesn’t completely mask the other – result is somewhere in-between • Codominance • Neither allele completely masks the other – result is a little of each • Multiple alleles • More than one allele for a trait • Polygenic traits • More than two genes control a trait • Sex-linked genes • The gene is located on the X chromosome

  2. Environment • Remember that the phenotype is only partly determined by its genotype. • Environment also plays a role: • Nutrition • Exercise

  3. Complete Dominance • Trait: Positive/negative blood type • Alleles: + and – • Type of Heredity: Complete dominance (+ is dominant) • Problem: A heterozygous female crosses with a homozygous recessive male • Find: • Possible genotypes of offspring • Genotypic percent • Possible phenotypes of offspring • Phenotypic percent

  4. Incomplete Dominance • Trait: Texture of hair (fictional) • Alleles: H (curly) & h (straight) • Type of Heredity: Incomplete dominance (neither allele completely masks the other – phenotype is in-between) • Problem: A curly-haired female crosses with a wavy-haired male • Find: • Possible genotypes of offspring • Genotypic percent • Possible phenotypes of offspring • Phenotypic percent

  5. Codominance • Trait: Human blood type • Alleles: A (codominant), B (codominant), O (recessive) • Type of Heredity: Codominance (both alleles share dominance – neither masks the other) • Problem: A female with heterozygous A-type blood crosses with a male with heterozygous B-type blood • Find: • Possible genotypes of offspring • Genotypic percent • Possible phenotypes of offspring • Phenotypic percent

  6. Multiple alleles • Manygenes have more than two possible alleles • Do you think that this means an individual can inherit more than two alleles? • NO! There are just more than two possible alleles to be inherited • one from mom, one from dad • For example, human blood type • Alleles A, B, & O

  7. Polygenic traits • Traits controlled by two or more genes • Skin color – 4 genes identified so far • Eye color • Shape of eyes and ears • Height • Many, many more

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