LESSON #10MENDEL DID NOT EXPLAIN EVERYTHING

COMPLEX PATTERNS OF INHERITANCECODOMINANCE, INCOMPLETE DOMINANCE, MULTIPLE ALLELES, SEX-LINKED TRAITS

CODOMINANCE

Both alleles are expressed in the

heterozygous condition.

Genotyp RR RW WW

Phenotyp

e

Red

petals

Red and

white

petals

White

petals

Red (R)

White (W)

Possible alleles:

Gene: Flower petal color

Red =

White

INCOMPLETE DOMINANCE

The heterozygous phenotype is an intermediate phenotype between the two homozygous phenotypes.

Red (CR )

White (C W )

Genotype CRCR CRC W C WC W

Phenotype Red flowers Pink flowers White flowers

Possible alleles:

Gene: Flower color

INCOMPLETE DOMINANCE: DOES NOT FOLLOW MENDEL’S RESULTS

MULTIPLE ALLELES

One gene can have many different variants

or alleles. The relationship between the

allele pair is unique.

ERYTHROCYTE PHENOTYPES: ABO BLOOD GROUPS

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

e

Blood

type A

Blood

type A

Blood

type

AB

Blood

type B

Blood

type B

Blood

type O

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”.

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.