Complex patterns of Inheritance

1. LESSON #10
MENDEL DID NOT EXPLAIN EVERYTHING

2. COMPLEX PATTERNS OF INHERITANCE
CODOMINANCE, INCOMPLETE DOMINANCE, MULTIPLE ALLELES, SEX-LINKED TRAITS

3. CODOMINANCE
 Both alleles are expressed in the
heterozygous condition.
Gene: Flower petal color
Genotyp RR RW WW
Phenotyp
e
Red
petals
Red and
white
petals
White
petals
Red (R)
White (W)
Possible alleles:
Red =
White

4. INCOMPLETE DOMINANCE
 The heterozygous phenotype is an
intermediate phenotype between the two
homozygous phenotypes.
Red (CR )
White (C W )
Gene: Flower color
Possible alleles:
Genotype CRCR CRC W C WC W
Phenotype Red flowers Pink flowers White flowers

5. INCOMPLETE DOMINANCE: DOES NOT FOLLOW MENDEL’S RESULTS

6. MULTIPLE ALLELES
 One gene can have many different variants
or alleles. The relationship between the
allele pair is unique.

7. ERYTHROCYTE PHENOTYPES: ABO BLOOD GROUPS

8. BLOOD TYPE ALLELES, GENOTYPE AND PHENOTYPE
Possible alleles
Antigen A (IA)
Antigen B (IB)
No Antigen (i)
IA = IB
IA > i
IB > i
Genotyp IAIA IAi IAIB IBIB IBi ii
Phenotyp
Blood
Blood
e
type A
type A
Blood
type
AB
Blood
type B
Blood
type B
Blood
type O

10. RHESUS FACTOR
 Antigen Rh (there are different types) may also be present on the RBC’s wall.
 If a person does not have Antigen Rh, he or she will develop antibodies Anti-Rh if they come
into contact with RBC that do have Antigen Rh.
 New research has proved that there are different Rh antigens and that an individual may carry
all, some or none.
 For further knowledge on Rh read the article on “Learning Extra”.

11. HEMOLYTIC DISEASE OF THE NEWBORN
 Women who are negative for a Rhesus factor
antigen and have had a child that is positive
for that antigen, may develop antibodies anti-
Rh when part of the baby’s blood passes to
the mother during birth.
 If this happens (development of antibodies
anti-Rh), in a following pregnancy the
newborn could suffer the hemolytic disease if
he or she is Rh+.
 The mother’s antibodies anti-Rh will attack and kill
the fetus’ red blood cells.
 To avoid this, the woman will be treated with
artificial antibodies during the delivery of every
Rh+ baby.
 The woman will hence not develop these
antibodies.