Transcript Multiple Alleles

Multiple Alleles
Multiple Alleles
• More than 2 alleles for a gene
• Dominance hierarchy (one allele dominates
over the other)
• Ex. Fruit Fly eye colour
– 4 alleles: Red, Apricot, Honey, White
– To show dominance hierarchy use first letter of
the gene name (E=Eye colour) and a superscript to
reflect how dominant it is (1 is most dominant)
Multiple Alleles
Red Eyes (E1)= Dominant to all (E1E1, E1E2, E1E3,E1E4)
Honey (E3): Dominant over white (E3E3, E3E4)
Apricot (E2): Dominant over honey & white
(E2E2, E2E3,E2E4)
White (E4): E4E4
Multiple Alleles
• Red Eyes crossed with honey eyes
• Red Eyes= E1E1 Honey Eyes= E3E3
E1
E1
E3
E1E3
E1E3
E3
E1E3
E1E3
Genotype: E1E3
Phenotype: Red Eyes
A more complicated example…
E2E3= Apricot eye colour (apricot is dominant over honey)
E3E4= Honey eye colour (honey is dominant over white)
E2
E3
E3
E2E3
E3E3
E4
E2E4
E3E4
Genotype Possibilities: ?
Phenotype Possibilities: ?
Co-Dominance
• When both alleles are expressed
– Ex. Spotted chicken
– Black and white feathers
Co-Dominant
• There is NO dominant allele
• Both alleles are expressed
– Ex. Black Chicken (FBFB), White Chicken (FWFW)
Black (FB)
Black (FB)
White (FW)
FBFW
FBFW
White (FW)
FBFW
FBFW
• Result= Spotted Chicken!
Blood Types
• Four possible blood types: A, B, AB, O
• Multiple alleles and co-dominance
– “A” allele (IA) codes for galactosamine on blood cell
membrane (allows your body to recognize it as its own)
– “B” allele (IB) codes for galactose
– “O” allele (i) codes for neither
• Both IA and IB are dominant over i, but neither is
dominant over the other
– IAIB: both galactosamine and galactose are expressed
Blood Types
•
•
•
•
A blood type: IAIA, IAi
B blood type: IBIB, IBi
O blood type: ii
AB blood type: IAIB
Example
IA
IB
IB
I AI B
IBIB
i
I Ai
IBi
Another Example
Example
IA
i
IB
I AI B
IBi
i
I Ai
ii
Resulting Blood Types?
Donating & Receiving Blood
• Giving blood:
• Getting Blood
- Type O: can only get blood from O
– Type O: universal donor
– Type A: can give to A and AB - Type A: can only get from A or O
- Type B: can only get from B or O
– Type B: can give to B and AB
- Type AB: can receive from anyone
– Type AB: can give to AB
Incomplete Dominance
• The alleles blend to form a different
heterozygous phenotype
– i.e., a red and white flower make a pink flower
– Red: CRCR White: CWCW
CR
CR
CW
CRCW: pink
CRCW: pink
CW
CRCW: pink
CRCW: pink