Multiple Alleles, Lec 11&12

7/28/2019 Multiple Alleles, Lec 11&12

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Genes which have more than two

alleles


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Since the information stored in any geneis extensive, mutations can modify thegene in many ways. Each mutationalchange has the potential for producing a

different allele. Therefore for any genethe number of alleles within members ofa population of individuals is notnecessarily restricted to two. When three

or more alleles of the same gene arefound, multiple alleles are said to bepresent, creating a characteristic mode ofinheritence.


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Multiple alleles can be studied only inpopulations.

The best examples of multiple allelic

system have been observed in coatcolour of rabbits, wings of drosophila, selfsterility in nicotiana and blood groups inman


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Coat color in rabbits- agouti,chinchilla, Himalayan, albino.


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Coat color in rabbits is determined byalleles of the C gene Four different alleles

exist C = full coat color

cch = chinchilla

ch = himalayan

c = albino

Any particular rabbitpossesses only twoalleles

5


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Dominant/recessive relationshipsbetween coat color alleles C is dominant to cch, ch, and c

cch

is recessive to C, but incompletelydominant to ch, and c

ch is recessive to C and cch, but dominant c

c is recessive to C, cch, ch

C > cch

> ch

> c

6


7/17

A series of multiple alleles for self-sterilityin tobacco was reported by E.M. East.Self sterility would mean that the pollen

from a plant will not be able to bringabout fertilization in the ovules of thesame plant.


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Lecture 12

25/7/12


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Phenotype

(Blood Type

Genotype

Blood Groups

Antigen on

Red Blood Cell

Safe Transfusions

To From


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Blood type is an example of a traitdetermined by a single gene. Each of ushas two copies of the gene for blood type

on chromosome pair number 9. One copyis inherited from our mother, the otherfrom our father. There are three versions(called alleles) of this gene: A, B, and

O. A persons blood type is determined bywhich allele he/she inherits from eachparent. The genetic constitution of anorganism is called the genotype.


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The phenotype refers to the visibleproperties of an organism that areproduced by the interaction of the

genotype and the environment. In thiscase, the A, B, O allele combination aperson has is their genotype, while theirblood type is their phenotype.


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In humans the blood groups are producedby various combinations of three allelesIA, IB, and i. Blood type A is caused by

either IA

IA

or IA

i; type B by IB

IB

or IB

i; type ABby IA IB; and type O by i i. Suppose a childis of blood type A and the mother is oftype 0. What type or types may the

father belong to? Suppose a father of blood type B and a

mother of blood type O have a child oftype O. What are the chances that theirnext child will be blood type O? Type B?


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An archeologist discovers an unopenedtomb in Egypt. Inside the tomb, he findsthe mummies of two adults and two

children.Inscriptions identify the two adults as

the chief scribe and his wife. Theinscriptions tell how their son and his

best friend drowned in the Nile Riverwhen their boat overturned. Themummies are so well preserved that labtechnicians are able to type their blood.

Both adults are type B. Child 1 is type A.


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What are the possible blood types of achild who's parents are bothheterozygous for "B" blood type?

Determine the possible genotypes &

phenotypes with respect to blood type fora couple who's blood types arehomozygous A & heterozygous B.

A test was done to determine the

biological father of a child. The child'sblood Type is A and the mother's is B. P1has a blood type of O, & P2 has bloodtype AB. Which is the biological father?


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This is an extremely rare ABO groupwhich derives the name "Bombay"because it was first discovered to exist

among some people living in the regionof Bombay, India. Although the group ismore likely to occur in East Indians, it is avery rare group even among this

population. Also, it is not restricted toEast Indians and has been found to existin Caucasians, Negroes, Japanese, etc.


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Bombay people would be incompatiblewhen crossmatched with red cells of allnormal ABO groups (groups O, A, B and

AB). If they require blood transfusion, they

must receive blood from anotherBombay. Donors must be sought among

their blood relatives (especially siblings)or from the rare donor file maintained bythe Red Cross.


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Inheritance: The Bombay group (Oh)

results from the inheritance of two rarerecessive h genes which occur at a locus

other than the ABO gene locus. Becausethe h gene is very rare, Bombays oftenresult from consanguineous matings inwhich parents are blood relatives (e.g.,

first cousins). Whenever inbreedingoccurs, the proportion of rarehomozygotes increases in frequency

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Multiple Alleles, Lec 11&12