Transcript (PowerPoint)

Beyond Mendelian Genetics
Mendel was lucky
• Monogenetic traits  controlled by one
pair of alleles
• Polygenetic traits  Controlled by more
than one pair of alleles
e.g. skin color (7 sets of alleles)
Incomplete Dominance
Example trait = flower color in 4 o’clock flowers
• Three phenotypes
WW=white flowers
RR=red flowers
RW=Pink flowers
Kinda like mixing
paint
Codominance
Example trait = Coat color in some horses
Three phenotypes
• BB=black
• WW=white
• BW=Roan (Both
black and white
hairs)
Kinda like mixing
different colored
marbles
Multiple Alleles
Example trait = Blood type (ABO system)
• More than 2 alleles for a trait
• Each person still has only two of those
alleles
• FOUR phenotypes
Multiple Alleles
Example trait = Blood type (ABO system)
The Alleles
IA
 codes
for “A” antigen
IB  codes for “B” antigen
i  codes for neither antigen
This allele codes
for “nothing” and is
therefore recessive
(An antigen is a receptor molecule on surface of cell used to recognize
self and non-self. Non-self antigens initiate the immune response)
Multiple Alleles
Example trait = Blood type (ABO system)
Genotype
Phenotype
IA IA
Type A blood
IA i
Type A blood
IB IB
Type B blood
IB i
Type B blood
IA IB
Type AB blood
ii
Type O blood