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Extended inheritance patterns
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Extended inheritance patterns

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  • 1. Extended Inheritance Patterns
  • 2. Other Inheritance Patterns• Incomplete dominance – Heterozygosity at a locus produces a third 3 phenotype intermediate to the two homozygous phenotypes• Co-dominance – Heterozygosity at a locus produces a single unique phenotype different from either homozygous condition• Overdominance – Heterozygosity at a locus creates a phenotype that is more beneficial or more deterimental than homozygosity of either locus with any allele
  • 3. Other Inheritance Patterns• Sex-linked – inheritance of genes on that are unique to a sex chromosomes• Sex-influenced – An allele is expressed differently in each sex. Behaving dominantly in one sex and recessively in the other• Sex-limited – An allele is only expressed in one or the other sex
  • 4. Complete Dominance/Recessiveness• recessive allele does not affect the phenotype of the heterozygote• two possible explanations – 50% of the normal protein is enough to accomplish the protein’s cellular function – The normal gene is “up-regulated” to compensate for the lack of function of the defective allele • The heterozygote may actually produce more than 50% of the functional protein
  • 5. Incomplete Dominance• heterozygote exhibits a phenotype intermediate to the homozygotes• Also called intermediate dominance or dosage effect• Example: – Flower color in the four o’clock plant governed by 2 alleles • CR = wild-type allele for red flower color • CW = allele for white flower color
  • 6. Incomplete Dominance
  • 7. 1:2:1 phenotypic ratio NOT the 3:1 ratio observed in simple Mendelian inheritance In this case, 50% of the CR protein is not sufficient to produce the red phenotypeFigure 4.2
  • 8. Incomplete Dominance• complete or incomplete dominance can depend on level of examination
  • 9. Multiple Alleles• The term multiple alleles is used to describe situations when three or more different alleles of a gene exist• Examples: – ABO blood – Coat color in many species – Eye color in Drosophila
  • 10. Multiple Alleles• ABO blood phenotype is determined by multiple alleles• ABO type result of antigen on surface of RBCs – Antigen A, which is controlled by allele IA – Antigen B, which is controlled by allele IB – Antigen O, which is controlled by allele i N-acetyl- galactosamine
  • 11. Co-dominance• Alleles IA and IB are codominant• They both encode functional enzymes and are simultaneously expressed in a heterozygous individual• Allele i is recessive to both IA and IB
  • 12. Multiple Alleles• coat color in rabbits – C (full coat color) – cch (chinchilla pattern of coat color) • Partial defect in pigmentation – ch (himalayan pattern of coat color) • Pigmentation in only certain parts of the body – c (albino) • Lack of pigmentation
  • 13. Multiple Alleles• Dominance hierarchy will exist for multiple alleles called an allelic series – allelic series for ABO type • IA = IB > i – allelic series for rabbit coat color alleles : • C > cch > ch > c
  • 14. Conditional Mutations• The ch allele is a temperature-sensitive conditional mutant – The enzyme is only functional at low temperatures – Therefore, dark fur will only occur in cooler areas of the body
  • 15. Overdominance• Overdominance is the phenomenon in which a heterozygote is more vigorous than both of the corresponding homozygotes• Example: – Sickle-cell heterozygotes are resistant to malaria – increased disease resistance in plant hybrids

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