Incomplete Dominance Codominance Multiple Alleles

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Incomplete DominanceCodominanceMultiple Alleles

• In a nutshell!

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Dominant/Recessive

• One allele is dominant over the other (capable of
  masking the recessive allele)

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Problem Dominant/Recessive

• In pea plants, purple flowers (W) are dominant
  over white flowers (w) show the cross between two
  heterozygous plants.

W w
GENOTYPES

- WW (1) Ww (2) ww (1) - ratio 121
W w
PHENOTYPES
- purple (3) white (1) - ratio 31
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Incomplete Dominance

• A third (new) phenotype appears in the
  heterozygous condition.
• Flower Color in 4 Oclocks

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Problem Incomplete Dominance

• Show the cross between a pink and a white flower.

GENOTYPES

- Rr (2) rr (2) - ratio 11

PHENOTYPES
- pink (2) white (2) - ratio 11
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Codominance

• The heterozygous condition, both alleles are
  expressed equally
• Sickle Cell Anemia in Humans

sick
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Problem Codominance

• Show the cross between an individual with
  sickle-cell anemia and another who is a carrier
  but not sick.

N S
GENOTYPES
- NS (2) SS (2) - ratio 11
S S
PHENOTYPES
- carrier (2) sick (2) - ratio 11
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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?
• IA, IB, i

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Rules for Blood Type

• IA A allele IB B allele i O allele
• A and B are codominant that is why they are
  both capital letters.
• IA IA Blood Type A
• IB IB Blood Type B
• IA IB Blood Type AB
• A and B are dominant over O
• IA i Blood Type A
• IB i Blood Type B
• ii Blood Type O

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Problem Multiple Alleles

• Show the cross between a mother who has type O
  blood and a father who has type AB blood.
• Key
• ii Homozygous
• Blood Type O
• IAIB Heterozygous
• Blood Type AB

IA IB
i i
GENO/PHEN/RATIOS

• IAi Blood Type A 12
• IBi Blood Type B 12

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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.
• Key
• IBi Heterozygous
• Blood Type B
• IAi Heterozygous
• Blood Type A

IA i
IB i
GENO/PHENO/RATIOS -IAIB Blood Type AB
14 -IAi Blood Type A 14 -IBi Blood
Type B 14 -ii Blood Type O 14