The document discusses the concept of multiple alleles, illustrated through examples like rabbit coat color and the ABO blood group system in humans. It also explains lethal alleles, which can cause death in organisms under certain genetic combinations, categorizing them into recessive, dominant, conditional, semi-lethal, and semi-dominant alleles. Key examples include yellow coat color in mice and Huntington's disease in humans.

1. MULTIPLE GENE
AND
LETHALALLELE
Presented To-
Dr. Kshetrimayum Mahesh Singh
Presented By-
Katchanchi Ch Marak
2023/VJ/072023/VJ/O7 J
2023/VJ/O7 /O7

2. MULTIPLE ALLELES
 When more than two different form of a given gene
exist in a species, it is referred to as multiple alleles.
 These alleles can occupy on the same locus on a
chromosome, but an individual organism can only
carry two of these alleles (one on each homologous
chromosome).

3. Coat Color in Rabbits
The rabbits may have the following colours :
1. Full colour/Agouti (brownish grey)
2. Chinchilla ( Silvery grey )
3. Himalayan – white with black extremities
4. Albino – complete white

4. CC, Ccch
, Cch
, Cca
- Agouti (wild type)
cch
, cch
, cch
ch
, cch
c - Chinchilla (salivary grey hair)
ch
ch
, ch
c - Himalayan (white except black feet nose ear tail)
cc - Albino (complete white).

6. ABO blood group system in humans
 The first case of multiple alleles demonstrated in man was the ABO blood
group system by Karl Landsteiner ( University of Vienna) in 1900.
 In 1930 He belatedly received the Nobel Prize for this discovery.
 The ABO locus has three common alleles of a single gene IA
, IB
, IO
(located on chromosome 9) forming four different phenotypes and 6
genotypes.
 IA and IB, are co-dominant and IO is recessive to both IA and IB

7. Phenotype Genotype Antigen
A IA
IA
,IA
IO A
B IB
IB
,IB
IO B
AB IA
IB AB
O IO
IO Neither

8. Lethal Alleles
A lethal allele is a gene variant (allele) that can cause the death of
an organism if it is present in certain genotypic combinations.
These alleles usually result from mutations in essential genes-
genes required for survival. Depending on their mode of
expression, lethal alleles can prevent development or cause death
at different stages of an organism's life.

10. Types of Lethal Alleles
1.Recessive Lethal Alleles:
Recessive lethal alleles are gene variants that cause death only when present in a homozygous
state (e.g., aa). Heterozygous individuals (Aa) typically survive, although they may exhibit a
phenotype associated with the allele.
Examples of Recessive Lethal Alleles:
1. Yellow Coat Color in Mice:
• Allele: AY
• Genotypes and Phenotypes:
►AY
AY
: Lethal (embryonic death)
►AY
A: Yellow coat
► AA: Normal coat color
2. Manx Cats:
• Phenotype: Shortened tail or no tail.
• Genotypes and Phenotypes:
► Homozygous (lethal): Death in utero.
► Heterozygous: Manx phenotype.

11. 2.Dominant Lethal Alleles:
Dominant lethal alleles are gene variants that cause death when present in a
single copy (heterozygous, Aa) or in two copies (homozygous, AA). These
alleles are typically rare because they can prevent the affected individuals
from surviving long enough to reproduce, unless the lethal effect manifests
after the reproductive age.
Examples of Dominant Lethal Alleles:
1.Huntington's Disease (Humans):
•Caused by mutations in the HTT gene.
•Symptoms include progressive neurological degeneration, typically
appearing in mid-life (35-50 years).
•Individuals often have children before symptoms appear, allowing the allele
to persist in populations

12. 3.Conditional Lethal Alleles:
Conditional lethal alleles are gene variants that cause death only under
specific environmental or physiological conditions. In the absence of these
conditions, the organism carrying the allele can survive.
One example of a conditional lethal is favism, a sex-linked inherited condition
that causes the carrier to develop hemolytic anemia when they eat fava beans.
4. Semi-Lethal Alleles:
Semi-lethal alleles are gene variants that cause death in only a portion of the
individuals carrying the allele. While some organisms with the genotype
survive, others do not, due to factors like genetic background, environmental
influences, or incomplete penetrance.
An example of semi-lethal alleles is dexter breed of cattle
Kerry type → normal(kk)
Bulldog appearance → death(KK)
Dexter → creeper(Kk)

13. 5.Semi-Dominant Alleles:
A semi-dominant allele (also known as an incomplete
dominant allele) is a type of allele where the heterozygous
phenotype is intermediate between the two homozygous
phenotypes. It shows a dose-dependent effect, meaning the
number of copies of the allele influences the phenotype.
Example – creeper bird

14. Thank
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