This document discusses multiple allelism, which refers to more than two alternative allelic forms of a gene occupying the same locus. It provides examples of multiple allelism in eye color in Drosophila, with 14 alleles producing different shades from white to red, and in human blood groups with the A, B, and O alleles. The characteristics of multiple alleles are described, including that only two alleles are present per individual. Multiple allelism in inheritance of blood groups and determining blood group combinations in offspring are also covered.

1. MULTIPLE
ALLELISM
Ms. RENU
Asst. Prof. (Zoology)

2. Multiple Allelism?
 More than two alternative allelic forms of gene
occupy the same loci in a pair of homologous
chromosomes in the population are called
multiple alleles.
 Determination of a trait by more than two alleles
is called multiple allelism.
 All the variants or alleles of a gene may be
originated by mutation of a single wild type gene.

3. Characteristics
 Multiple alleles occupy the same locus with in the
homologous chromosomes. It means only one
member of the series is present in a given
chromosome.
 Since only two chromosomes of each type are
present in each diploid cell, only two genes of the
multiple series are found in a cell and also in a
given individual.
 The gametes contain only one chromosome of
each types, therefore, only one allele of the
multiple series in each gamete.

4. Contd…
 Crossing over does not occur in the multiple
alleles.
 Multiple alleles control the same character, but
each of them is characterized by different
manifestation.
 When any two of the mutant multiple alleles are
crossed, the phenotype is mutant type and not
the wild type.

5. Multiple Alleles in Eye Colour of
Drosophila
 Found 14 alleles for eye colour which produce
various shades from white to red.
 Red eye colour is normal(wild type)- dominant to
others.
 Others shades are- wine, coral, blood, cherry,
apricot, eosin, buff, tinged, honey, ecru, pearl,
ivory and white.

6. A cross between red fly and any mutant fly produces F1
hybrid flies having red eye colour because red is dominant
over all mutants.

7. A cross between any two mutant flies produce F1
hybrids having intermediate colour.
For example:-
Pure Eosin Eye Colour Pure White Eye Colour
X
Intermediate Pale Eosin Colour (F 1 generation)
(100% hybrid)
This shows the Incomplete Dominance because the genes for eosin and
white colour are not dominant or not recessive.

8. Multiple Allelism In Blood Groups
 Human blood groups was reported by Dr. Karl Landsteiner
in 1900. (father of blood groups)
 Presence of two typesof proteins in human blood:-
Antigens Or Agglutinogen:- glycoprotein present on surface
of RBCs called corpuslces factor.
Antibody Or Agglutin:- gamma-globulin present in blood
plasma called plasma factor.

9. Detection of A, B, and O blood type in
humans determined by multiple alleles and
two alleles acting co-dominantly over third

10. ABO donor recipient combinations. The tick mark
indicates compatibility in blood transfusion and cross
indicates incompatibility.

11. Phenotype Genotype
Antigen (present
on red blood cells)
Antibody (found
in the serum)
O ii None anti-A and anti-B
A IAIA, IAi A antigen anti-B
B IBIB, IBi B antigen anti-A
AB IAIB
Both A and B
antigens
None
Different types of blood groups
O- Blood Group is called universal donor- has no antigen & can donate
its blood to any person.
AB- Blood Group is universal recipient- has no antibody in their blood
plasma.

12. Inheritance of ABO Blood Groups
 Bernstein discovered that the ABO blood grouping
in an inherited characteristic and involves multiple
allelism.
 Genotypes of four types of blood groups:-

13. Possible Blood Groups of the Children of
Different Blood Groups

14. Possible Blood Groups of Offsprings
and Their Parents

15. Significance of Knowledge of Blood
Groups
 By knowing of blood groups of parents, blood
groups of their children can be predicted.
 Helps saving innocent people involved in murder
cases and in identifying the real murderers.
 Helps in safe blood transfusion.
 Used to settle cases of disputed parentage in mix
up cases in hospitals.

16. Rhesus (Rh) Blood Group System
 Rh-Factor:- antigenic protein present on the
surface of red blood cells in human beings.
 First discovered by Landsteiner & Weiner(1940) on
plasma membrane of RBCs of rhesus monkey.
 Also found in 85% American & 93% of Indians-
called Rh-positive (Rh+).
 Person with no Rh-factor on the surface of their
RBCs- called Rh-negative (Rh-).
 Rh-factor is controlled by a pair of genes- R & r.(R
gene is dominant and control synthesis of Rh-factor,
r-gene cannot synthesize Rh-factor.)

18. Incompatibility during pregnancy

19. Importance of Rh-factor
 Transfusion of Rh+ donor blood into Rh- recipient
blood causes clumping of donor’s RBCs
 It causing blocking of capillaries and death
 No complication occur in first transfusion but
subsequent transfusion causes this condition
 So, Rh-factor compatibility also considered
together with ABO blood group before blood
transfusion