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Incomplete Dominance Multiple Alleles

Incomplete Dominance Multiple Alleles. In a nutshell!. PP = purple. Pp = purple. pp = white. Review: Dominant/Recessive. One allele is dominant over the other (capable of masking the recessive allele) Example: Purple flowers are dominant over white. PP. Pp. Pp. pp.

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Incomplete Dominance Multiple Alleles

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  1. Incomplete DominanceMultiple Alleles In a nutshell!

  2. PP = purple Pp = purple pp = white Review: Dominant/Recessive • One allele is dominant over the other (capable of masking the recessive allele) • Example: Purple flowers are dominant over white

  3. PP Pp Pp pp Review Problem: Dominant/Recessive • In pea plants, purple flowers (P) are dominant over white flowers (p) show the cross between two heterozygous plants. P p GENOTYPES: - PP (1); Pp (2); pp (1) - ratio 1:2:1 P p PHENOTYPES: - purple (3); white (1) - ratio 3:1

  4. Review of Monohybrid Crosses • Remember, monohybrid crosses involve only ONE trait • Practice… In fruit flies, red eyes are dominant over white eyes. • Cross a white-eyed fly with a homozygous dominant red-eyed fly. • Cross two heterozygous red-eyed flies. Draw a Punnett square for each cross, and determine the genotypic and phenotypic ratios.

  5. r r R r Rr Rr R RR Rr R R Rr Rr r Rr rr

  6. Can you determine the genotype • of a white-eyed fly just by looking at it? Why? • Yes- it’s rr • There is only one genotype for white eyes • Can you determine the genotype • of a red-eyed fly just by looking at it? Why? • No- it could be RR or Rr • There are two genotypes for red eyes • How could you determine the genotype of the red-eyed fly? • Perform a test cross

  7. Review of Monohybrid Crosses • What two organisms would you cross in the test cross? • The unknown red-eyed fly with a white eyed fly • If the red-eyed fly was RR, what would the offspring of the test cross look like? • All of the offspring would have red eyes • If the red-eyed fly was Rr, what would the offspring of the test cross look like? • Half of the offspring would have red eyes, half would have white eyes

  8. RR = red rr = white Rr = pink Incomplete Dominance • A third (new) phenotype appears in the heterozygous condition. • Flower Color in 4 O’clocks

  9. R r r r Rr Rr rr rr Problem: Incomplete Dominance • Show the cross between a pink and a white flower. GENOTYPES: - Rr (2); rr (2); RR (0) - ratio 2:2:0 PHENOTYPES: - pink (2); white (2) Red (0) - ratio 2:2:0

  10. Multiple Alleles • There are more than two alleles for a trait • Blood type in humans • Blood Types? • Type A, Type B, Type AB, Type O • Blood Alleles? • A, B, O

  11. Rules for Blood Type • A and B are codominant • AA = • BB = • AB = • A and B are dominant over O • AO = • BO = • OO = Type A Blood Type B Blood Type AB Blood Type A Blood Type B Blood Type O Blood

  12. AO AO BO BO Problem: Multiple Alleles • Show the cross between a mother who has type O blood and a father who has type AB blood. O O GENOTYPES: - AO (2) BO (2) A B PHENOTYPES: - type A (2); type B (2) - ratio 2:2:0:0

  13. BO AB AO OO Problem: Multiple Alleles • Show the cross between a mother who is heterozygous for type B blood and a father who is heterozygous for type A blood. GENOTYPES: A O • AB (1); BO (1); • AO (1); OO (1) • - ratio 1:1:1:1:0:0 B O PHENOTYPES: • type AB (1); type B (1) • type A (1); type O (1) • - ratio 1:1:1:1

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