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Incomplete Dominance, Codominance, Sex-linked and Polygenic Inheritance

Incomplete Dominance, Codominance, Sex-linked and Polygenic Inheritance. Mendel ’ s Dominance. Mendel ’ s rule of dominance was complete dominance Homozygous dominant organisms have the dominant phenotype Heterozygous organisms have the dominant phenotype

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Incomplete Dominance, Codominance, Sex-linked and Polygenic Inheritance

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  1. Incomplete Dominance,Codominance, Sex-linked and Polygenic Inheritance

  2. Mendel’s Dominance • Mendel’s rule of dominance was complete dominance • Homozygous dominant organisms have the dominant phenotype • Heterozygous organisms have the dominant phenotype • Example: Both PP and Pp plants have the dominant PURPLE phenotype (P=purple and p=white flowers)

  3. Incomplete Dominance Offspring have an appearance somewhat in betweenthephenotypes of the two parents and neither allele is dominant. “Mixed” Blended R R F1 generation Rr Rr r r Rr Rr All Rr = pink (heterozygous pink)

  4. Incomplete Dominance Incomplete dominance occurs when two or more alleles influence the phenotype Neither allele is completely dominant over the other

  5. Incomplete Dominance

  6. Codominance BOTH allelesare expressedequally in heterozygous individuals. Use two capital letters for both alleles. Neither allele is dominant over the other. Usually phenotypes are stripes or spots.

  7. YOU tell me which type of dominance… Codominance!

  8. Type of Dominance? Incomplete Dominance!

  9. Type of Dominance? Incomplete Dominance!

  10. Codominance • Example:blood type • Determined by whether or not you have A or B proteins • IA = A protein • IB = B protein • I = no protein

  11. Codominance

  12. IB IB IAIB IAIB IA 1/2 = IAIB 1/2 = IBi i IBi IBi Codominance Problem • Example:homozygous male Type B (IBIB) • x heterozygous female Type A (IAi)

  13. IA IB IAi IBi i 1/2 = IAi 1/2 = IBi i IAi IBi Another Codominance Problem Example:male Type O (ii) x female type AB (IAIB)

  14. Codominance • Question:If a boy has a blood type O and his sister has blood type AB, what are the genotypes and phenotypes of their parents? boy - type O (ii) X girl - type AB (IAIB)

  15. IA i IAIB IB i ii Codominance • Answer: Parents: genotypes = IAi and IBi phenotypes = A and B

  16. Sex-linked Traits Traits (genes) located on the sex chromosomes Sex chromosomes are X and Y XX genotype for females XY genotype for males Many sex-linked traits carried on X chromosome

  17. X y XC X Sex – Linked Traits • Example: Colorblindness • If the mother carries the colorblindness gene on her X chromosome, her son could get it. • As long as one X chromosome is ok, a female will not express the trait XcX X y X X X y

  18. Sex-linked Traits Color- blindness XX chromosome - female Xy chromosome - male Example: Colorblindness Sex Chromosomes

  19. Polygenic Inheritance • Inheritance pattern controlled by two or more genes • Genes can be on the same chromosome or on different chromosomes • Genotypes written as AA, Aa, or aa except you will have three or more genes each with a dominant and recessive trait • Skin color is influenced by the additive effects of melanin by three to six genes. Eye color is also a result of melanin added from multiple genes.

  20. Gametes ABC ABc AbC Abc aBC aBc abC abc ABC AABBCC AABBCc AABbCc AaBBCC ABc AbC Abc AAbbcc aBC aaBBCc aBc abC abc aaBbcc Polygenic Inheritance of Skin Color The table shows typical ranges of skin color combinations. Other polygenic influenced conditions include Spina bifida and Cleft palate.

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