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  • MAIN QUESTION: How multiple alleles, incomplete dominance, co dominance is affecting the living world?
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  • WHEN HEREDITY FOLLOWS DIFFERENT RULES. 1.INCOMPLETE DOMINANCE APPEAREANCE OF A THIRD PHENOTYPE. -The phenotype is intermediate between two homozygous parents. Ex. Capital letters used for both alleles Snap dragons- red = RR, white= WW, pink = RW
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  • Incomplete dominance
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  • 2. Co dominance - expression of both alleles Occurs when alternative alleles are present in the genotype and fully observed in the phenotype. See.fig 12.8, pg.323
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  • Codominance in Humans Sickle-cell anemia sickle red blood cells slow blood flow, produce tissue damage and pain.
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  • 3. Multiple phenotypes from multiple alleles - traits controlled by more than two alleles. Ex. Pigeon feathers color
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  • Multiple Alleles in Humans Multiple alleles govern blood type Ex. ABO blood grouping system, where a single gene locus features multiple alleles- IA, IB, and i. Individuals carrying alleles for both A and B express both in the phenotype AB.
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  • GenotypePhenotype (blood group) I A I A or I A iA I B I B, or I B iB IAIBIAIB AB iiO Multiple Alleles in Humans THE BLOOD TYPE
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  • Sex determination: white board
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  • 4. Sex - linked inheritance 1919 T. Morgan research on Drosophila fruit flies; Traits controlled by genes located on sex chromosomes SEX-LINKED TRAITS. (X linked trait, Y-link trait) (X linked trait, Y-link trait) EX. The allele for eye colors are carried on the X chromosome.
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  • Sex-Linked Traits in Humans Red-green color blindness - caused by two recessive alleles from X chromosome. Hemophilia X linked disorder.
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  • 5. Polygenic inheritance The inheritance pattern of a trait that is controlled by two more genes. Ex. Skin color, height in humans, cob length in corn.
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  • 6. Changes in Chromosome Numbers It can affect autosomes Down syndrome (Trisomy 21) It can affect sex chromosomes XYY or XXX or XXY