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Complex Patterns of
Inheritance
Incomplete Dominance
• Neither allele is completely dominant nor completely
recessive.
•
•
Heterozygous phenotype is a mix between the two
homozygous phenotypes
Homozygous parental phenotypes not seen in F1
offspring
Phenotype: green
Genotype: B1B1
Phenotype: steel blue
Genotype: B2B2
Phenotype: royal blue
Genotype: B1B2
Incomplete Dominance
● What will be the possible traits of a cross
between two royal blue fish (B1B2)?
B1
B2
B1
B2
B1B1
B1B2
B1B2
B2B2
● Genotype1 B1B1: 2 B1B2: 1
B2B2
● Phenotype1 green: 2 royal
blue: 1 steel blue
Codominance
• Codominant alleles will both be completely
expressed.
• Codominant alleles are neither dominant nor
recessive.
• The ABO blood types result from codominant
alleles.
• Many genes have more than two alleles.
Codominance
● In some plants, flower
color is codominant.
○ Red flower genotype
= RR
○ White flower
genotype = WW
○ Red and white flower
genotype = RW
Codominance
● What would the possible phenotypes and
genotypes be in a cross between two bicolored plants?
R
W
● Genotype1 RR: 2 RW: 1 WW
● Phenotype1 red: 2 red & white: 1 white
R
W
RR
RW
RW
WW
Many genes may interact to produce one trait.
• Polygenic traits are produced by two or more
genes.
• An epistatic gene can interfere with other genes.
The environment interacts with genotype.
• Phenotype is a combination of genotype and
environment.
• The gender of sea turtles depends on both genes and
the temperature
• Height is an example of a phenotype strongly
affected by the environment.