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Incomplete Dominance and Codominance

Incomplete Dominance and Codominance. r. r. R. R. F1 hybrids have an appearance somewhat in between the phenotypes of the two parental varieties. Example: snapdragons (flower) red (RR) x white ( rr ) RR = red flower rr = white flower. Incomplete Dominance. r. produces the

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Incomplete Dominance and Codominance

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  1. Incomplete DominanceandCodominance

  2. r r R R • F1 hybrids have an appearance somewhat in between the phenotypes of the two parental varieties. • Example:snapdragons (flower) • red (RR) x white (rr) • RR = red flower • rr = white flower Incomplete Dominance

  3. r produces the F1 generation Rr Rr R R Rr Rr All Rr = pink (heterozygous pink) Incomplete Dominance r

  4. Incomplete Dominance

  5. Two alleles are expressed equally in multiple allelesin heterozygous individuals. • Example: blood type • 1. type A = IAIA or IAi • 2. type B = IBIB or IBi • 3. type AB = IAIB (equally expressed) • 4. type O = ii (recessive alleles) Codominance

  6. IA i 1/2 = IAIB (A & B = equally expressed) IAIB IBi IB 1/2 = IBi (B dominant over i) IB IAIB IBi • Example: homozygous male Type B (IBIB) X heterozygous female Type A (IAi) Codominance Problem

  7. 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)

  8. 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) Codominance

  9. Answer: Codominance

  10. 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 Sex-linked Traits

  11. fruit fly eye colour XX chromosome - female Xy chromosome - male Sex-linked Traits Example: Eye colourin fruit flies Sex Chromosomes

  12. Xr Xr XR Y • Example: Eye colourin fruit flies • (red-eyed male) x (white-eyed female)XRY x XrXr • Remember: the Y chromosome in males does not carry these traits. • RR = red eyed • Rr = red eyed • rr = white eyed • XY = male • XX = female Sex-linked Trait Problem

  13. Xr Xr XR Xr XR Xr XR Y Xr Y Xr Y Sex-linked Trait Solution: 50% red eyedfemale 50% white eyed male

  14. Female Carriers

  15. Genetic Practice Problems

  16. t t T T tall (TT) x dwarf (tt) pea plants Breed the P1 generation

  17. t t produces the F1 generation Tt Tt T Tt Tt T All Tt = tall (heterozygous tall) Solution: tall (TT) vs. dwarf (tt) pea plants

  18. T t T t tall (Tt) vs. tall (Tt) pea plants Breed the F1 generation

  19. T t produces the F2 generation Tt TT T 1/4 (25%) = TT 1/2 (50%) = Tt 1/4 (25%) = tt Tt tt t 1:2:1 genotype 3:1 phenotype Solution: tall (Tt) x tall (Tt) pea plants

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