Download Notes: Incomplete Dominance Phenotype is affected by many

Notes: Incomplete Dominance
Phenotype is affected by many different factors.
Phenotype can depend on interactions of alleles.
• In incomplete dominance, neither allele is completely
dominant nor completely recessive.
– Heterozygous phenotype is a blend between the two
homozygous phenotypes
– Homozygous parental phenotypes not seen in F1
offspring
Four o’clock plants
aka Carnations
• Homozygous plants are either red (RR) or white
(R’R’).
• Heterozygous (RR’) are pink.
This animation shows the cross between a black homozygous
dominant cat and a white homozygous recessive cat. This
results in a litter of all heterozygous gray cats.
• Codominant alleles will both be completely expressed.
– Codominant alleles
are neither
dominant nor
recessive.
– The ABO blood
types result from
codominant alleles.
Codominance
 This animation shows the cross between a black
homozygous recessive cat and a white homozygous
dominant cat. This results in a heterozygous litter of black
and white spotted kittens.
• Multiple alleles: exists when genes have more than two
alleles
– The ABO blood
types result from
multiple alleles that
are codominant
Many genes may interact to produce one trait.
• Polygenic traits are
produced by two or
more genes.
Order of dominance:
brown > green > blue.
• An epistatic gene can interfere with other genes by
overshadowing them for a particular trait.
Labrador Retriever Genetics
• Black is dominant to chocolate B or b
• Yellow is recessive epistatic (when present, it blocks the
expression of the black and chocolate alleles) E or e
Phenotype Possible Genotypes
BBEE BbEE
BBEe BbEe
bbEE bbEe
Bbee Bbee
bbee
The environment interacts with genotype.
• Phenotype is a combination
of genotype and
environment.
• Examples:
• sex of sea turtles
depends on both genes
and temperature