MULTIPLE ALLELISMMs. RENU Asst. Prof. (Zoology)

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.

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.

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.

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.

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

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.

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.

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

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

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.

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:-

Possible Blood Groups of the Children of Different Blood Groups

Possible Blood Groups of Offsprings and Their Parents

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.

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.)

Incompatibility during pregnancy

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