Multiple alleles occur when there are more than two alternative forms of a gene at a single locus. They arise through repeated mutation of the same gene. Examples include alleles for eye color in fruit flies and coat color in rabbits. ABO blood groups in humans are determined by three alleles - IA, IB, and i. IA and IB are codominant and determine antigen A or B, while ii is recessive and results in type O blood. In fruit flies, eye color is controlled by nearly 15 alleles including w for white and W for red. In rabbits, coat color alleles include C for full brown color, Cch for chinchilla gray, Ch for himalayan pattern, and c for albino

1. ATTIQ AFTAB
STREAM- INTEGRATED BOTANY
PRESENTATION ON-MULTIPLE ALLELES

2. MULTIPLE ALLELES
• More than two alternative forms (alleles) of a gene occupying the same
locus on a chromosome or its homologue are known as multiple alleles.
MODE OF ORIGIN
➢ Multiple alleles are produced due to repeated mutation of the same gene.
➢ Multiple alleles show meristic type of germinal variations.
➢ Meristic variation involves the number or arrangement of the parts

3. CHARACTERISTICS
• ➢ All of them are mutants of the same wild allele.
• ➢ All the multiple alleles of the gene occur on the same gene locus of the same
• chromosome or its homologue.
• ➢ Multiple alleles express different alternatives of a single trait.
• ➢ Different alleles may show codominance, dominance-recessiveness or
• incomplete dominance among themselves.

4. • ➢ There are more than two alleles of the same gene, for example:
• Alleles for eye colour in Drosophila
• 3 alleles for blood groups in humans
• 4 alleles for coat colour in rabbit.

5. ABO BLOOD GROUPS
• ➢ ABO blood group in human beings comprises four blood groups.
• ➢ Blood group:
• A
• B
• AB
• O

6. ABO BLOOD GROUPS
• ➢ Three blood groups A, B and O were discovered by Landsteiner while one
blood group AB was discovered by de Castello and Sturli.
• ➢ ABO grouping is based on the presence or absence of two surface antigens
on the RBCs namely A and B.
• ➢ Similarly, the plasma of different individuals contain two natural antibodies.

7. Antigen on RBCs
Antigen A Blood Group A
Antigen B Blood Group B
Antigen A and B Blood Group AB
Neither A nor B Blood Group O

8. The antibodies in your plasma do not react with the antigens on your blood cells

9. ALLELES FOR ABO BLOOD GROUPS
• ➢ The synthesis of surface antigens is controlled by following alleles,
designated:
IA
lB
I
➢ The i allele is recessive to both IA and IB.
➢ A person who is homozygous ii will have type O blood.
➢ A homozygous IAIA or heterozygous lAi individual will have type A blood
➢ The red blood cells of this individual will contain the surface antigen known as A.

10. • ➢ A homozygous IBIB or heterozygous IBi individual will produce surface antigen
B.
• ➢ A person who is IAIB will have the blood type AB and express both surface
• antigens A and B.
• ➢ Let’s consider the possible offspring between two parents who are IAi and IBi.
• ➢ The IAi parent makes IA and i gametes, and the IBi parent makes IB and i gametes.
• ➢ These combine to produce IAIB, IAi, IBi, and ii offspring in a 1:1:1:1 ratio.
• ➢ Persons with IAIB alleles have blood group AB because both IA and IB alleles
• are codominant.
• ➢ AB Blood Group is characterised by the presence of both antigen A (from IA)
• and antigen B (from IB) over the surface of RBCs.

11. EYE COLOUR IN FRUIT FLY-DROSOPHILA
• Eye colour in Drosophila is controlled by nearly
15 multiple alleles.
• ➢ The normal or wild type eye colour is red
represented by allele W.
• ➢ There is an allele w for white eye colour which
is recessive to all other alleles.

12. • ➢ Alleles of other eye colour traits are intermediate between the two.
• ➢ They show various types of codominance and incomplete dominance.
• ➢ These important alleles are
• ➢ wch (cherry),
• ➢ wi (ivory white),
• ➢ wco (coral),
• ➢ wbf (buff),
• ➢ wh (honey),
• ➢ wbl (blood),
• ➢ weo (eosine),
• ➢ ww (wine),
• ➢ wp (pearl)
• ➢ wsat (deep ruby)
• ➢ wa(orange)

14. COAT COLOUR IN RABBITS
• Agouti Type Coat
• Chinchilla Type Coat
• Himalayan Type Coat
• Albino Type Coat
• In rabbits coat colour is represented by 4 alleles— C, Ch, Cch and c.
• ➢ The coat of rabbit may have following different colours.

15. AGOUTI TYPE COAT
• Agouti is a brown large long legged wild type
burrowing rodent related to the guinea pig.
• ➢ It is a native of Central and South America.
• ➢ It has dark brown and uniform colour.
• ➢ The gene for full colour is represented by
capital letter C.

16. CHINCHILLA TYPE COAT
• ➢ The coat is silvery-gray and uniform in colour.
• ➢ The gene for chinchilla is represented as Cch.
• ➢ Chinchilla is a small South American rodent.
Himalayan Type Coat
➢ This type of coat is white except extremities
(nose, ears, feet and tail).
The gene for Himalayan coat is represented by Ch.

17. ALBINO TYPE COAT
• ➢ The albino coat totally lacks in pigmentation.
• ➢ The eyes of an albino also remain pink due to lack of
pigment in iris of eye.
• The gene for albino is represented by c.
• MULTIPLE ALLELES
The gene C for full colour is dominant over all other
alternatives.
➢ Chinchilla (Cch) is recessive to full colour but dominant to
others
(Himalayan and albino).
➢ Himalayan (Ch) is recessive to full colour and chinchilla but is
dominant over albino.

18. • ➢ The gene encodes an enzyme called tyrosinase, which is the first
enzyme in a metabolic pathway that leads to the synthesis of
melanin from the amino acid tyrosine.
• ➢ This pathway results in the formation of two forms of melanin.
• ➢ Eumelanin, a black pigment, is made first, and then
phaeomelanin, an
• orange/yellow pigment, is made from eumelanin.
• ➢ Alleles of other genes can also influence the relative amounts of
eumelanin and phaeomelanin.

19. • ➢ Differences in the various alleles are related to the function of tyrosinase.
• ➢ The C allele encodes a fully functional tyrosinase that allows the synthesis of
• both eumelanin and phaeomelanin resulting in a full brown coat color.
• ➢ The C allele is dominant to the other three alleles.
• ➢ The chinchilla allele (cch) is a partial defect in tyrosinase that leads to a
• slight reduction in black pigment and a greatly diminished amount of
• orange/yellow pigment, which makes the animal look gray.
• ➢ The albino allele, designated c, is a complete loss of tyrosinase, resulting in
• white color.

20. • ➢ The himalayan pattern of coat color, determined
by the ch allele, is an example of a temperature-
sensitive allele.
• ➢ The mutation in this gene has caused a change in
the structure of tyrosinase,
• so it works enzymatically only at low temperature.
• ➢ Because of this property, the enzyme functions
only in cooler regions of the body,primarily the
tail,the paws
and the tips of the nose and ears.

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