Download EXCEPTIONS TO MENDEL`S “LAW OF DOMINANCE”

EXCEPTIONS TO MENDEL’S
“LAW OF DOMINANCE”
Incomplete and Co-dominance
Incomplete Dominance
¨ 
When an allele is not completely dominant and an
intermediate phenotype is observed in a
heterozygous individual.
Incomplete Dominance in Four O’Clock Flowers
Incomplete Dominance in Four O’Clock Flowers
Co-Dominance
When both alleles are fully expressed in
the phenotype.
¨  Example: Cross a red cow (RR) with a
white cow (WW). What are the
genotypes and phenotypes of the
offspring?
¨ 
Co-dominance
X
Red
White
Roan
Multiple Alleles
Often there are more than two alleles for
a gene.
¨  Each individual inherits two alleles, but
there are more than two versions of the
allele in the population.
¨ 
Multiple Alleles in Rabbits
¨ 
¨ 
¨ 
¨ 
Full Color
C = Full Color; dominant
to all other alleles.
Cch = chinchilla; partial
defect in pigmentation;
dominant to ch and c
alleles.
ch = Himalayan; color in
certain parts of the body;
dominant to c allele.
c = albino; no color;
recessive to all other
Genotypes: CC, Ccch, or Cc
alleles.
Multiple Alleles in Rabbits
¨ 
¨ 
¨ 
¨ 
C = Full Color; dominant
to all other alleles.
Cch = chinchilla; partial
defect in pigmentation;
dominant to ch and c
alleles.
ch = Himalayan; color in
certain parts of the body;
dominant to c allele.
c = albino; no color;
recessive to all other
alleles.
Chinchilla
Genotypes: cch ch, cch cch,
or cch c
Multiple Alleles in Rabbits
¨ 
¨ 
¨ 
¨ 
C = Full Color; dominant
to all other alleles.
Cch = chinchilla; partial
defect in pigmentation;
dominant to ch and c
alleles.
ch = Himalayan; color in
certain parts of the body;
dominant to c allele.
c = albino; no color;
recessive to all other
alleles.
Himalayan
Genotypes: ch c, or ch ch
Multiple Alleles in Rabbits
¨ 
¨ 
¨ 
¨ 
C = Full Color; dominant
to all other alleles.
Cch = chinchilla; partial
defect in pigmentation;
dominant to ch and c
alleles.
ch = Himalayan; color in
certain parts of the body;
dominant to c allele.
c = albino; no color;
recessive to all other
alleles.
Albino
Genotype: cc
Polygenic Traits
Polygenic - traits that
are controlled by more
than one gene.
¨  Usually shows a range
of phenotypes.
¨  Ex. Height in humans,
skin color in humans.
¨