Dihybrid Crosses and Blood Typing. Dihybrid Crosses. Have space provided for 4 gamete alleles from two parents. YYRR Pure Dominant y yrr Pure Recessive Y – yellow R – round seeds F1 – 100 % 4:0 dominant for both traits Phenotype – 100% Yellow and Round. F1 Hybrid Cross. YyRr
YYRR Pure Dominant
Y – yellow R – round seeds
F1 – 100 % 4:0 dominant for both traits
Phenotype – 100% Yellow and Round
Phenotypes: Yellow and Round 9
Yellow and Wrinkled 3
Green and Round 3
Green and Wrinkled 1
Phenotype 9:3:3:1 but each trait by itself is still 3:1
YR 9:3 GR GR 3:1 GW
Co-dominance occurs in human heredity. Sickle cell anemia is controlled by co-dominance.
1) A antigens (type A blood)
2) B antigens (type B blood)
3) Both a and B antigens (type AB blood)
4) Neither A nor B antigens (type O blood)
There are 3 alleles that control blood type: A,B and O.
The usual way to represent alleles in a multiple allele system is to use the capital letter I to represent a co-dominant allele and a lower case i to represent a recessive allele.
IA represents dominant allele A
IB represents dominant allele B
i represents recessive allele O
Since there are 3 alleles, there are 6 possible genotypes:
1) IAIA 2) IAIB 3) IAi 4) IBIB 5) IBi 6) ii
The possible human phenotypes for blood group are type A, type B, type AB, and type O. Type A and B individuals can be either homozygous (IAIA or IBIB, respectively), or heterozygous (IAi or IBi, respectively).
The relationship between blood
type (phenotype) and genotype
is shown in the table to the left.
The mother (blood type A) and
father (blood type B) could be
either homozygous or heterozygous.
crosses are possible.
All four crosses must be
considered to determine
all potential offspring.
A blood test of either type AB or type O is more informative. Someone with blood type AB must have both the A and B alleles. The genotype must be AB. Someone with blood type O has neither the A nor the B allele. The genotype must be OO.