Pleiotropy is a phenomenon where a single gene influences multiple phenotypic traits. It was first defined by Ludwig Plate in 1910 and studied further by Hans Gruneberg, who divided it into "genuine" and "spurious" types. There are three main types of pleiotropy: gene pleiotropy focuses on a gene's multiple functions; developmental pleiotropy on a mutation's effects on traits; and selectional pleiotropy on a mutation's fitness effects. Examples include sickle cell anemia caused by an HBB gene mutation leading to organ failure, and phenylketonuria caused by a phenylalanine hydroxylase enzyme gene mutation increasing amino acid levels dangerously. Marfan syndrome results from

1. PLEIOTROPY
By: Manohari M Kulkarni
BSc 1st semester {BBG section}

2.  What is Pleiotropy?
• A single pair of gene influences multiple, seemingly unrelated phenotypic traits, this
phenomenon is called Pleiotropy.
• The genes which cause Pleiotropy are called “Pleiotropic Genes”

3. Brief History of PLEIOTROPY
Pleiotropic traits had been previously recognized in the scientific community but had not been
experimented on until Gregor Mendel's 1866 pea plant experiment.
 Mendel recognized that certain pea plant traits such as seed coat colour, flower colour, and axial
spots, seemed to be inherited together.
The term "Pleiotropy" was first coined by Ludwig Plate in his Festschrift, which was published in
1910
Ludwig Plate originally defined Pleiotropy as occurring when
"several characteristics are dependent upon ...
[inheritance]; these characteristics will then always
appear together and may thus appear correlated"

4. Hans Gruneberg
• the first to study the
mechanisms of Pleiotropy
•dividing Pleiotropy into two
distinct types: "genuine" and
"spurious" Pleiotropy.
George Beadle and
Edward Tatum
• further invalidated Gruneberg's definition
of "genuine" Pleiotropy, advocating
instead for the "one gene-one enzyme"
hypothesis that was originally introduced
by French biologist Lucien in 1903.
Ernst Hadorn
• Hadorn partitioned Pleiotropy
into a "mosaic" model (which
states that one locus directly
affects two phenotypic traits)
Through subsequent
research, it has been
established that Gruneberg's
definition of "spurious"
Pleiotropy is what we now
identify simply as "Pleiotropy"

5. Molecular-Gene Pleiotropy
Developmental Pleiotropy
Selectional Pleiotropy
Reasons for Pleiotropy

6. Gene Pleiotropy
 Also called Molecular-gene Pleiotropy
 It focuses on number of functions of a particular gene
 Those functions are determined by the number of
traits and biochemical factors impacted by a gene.
 . Gene pleiotropy occurs when a gene product
interacts with multiple other proteins or catalyzes
multiple reactions.

7. Developmental Pleiotropy
• focuses on mutations and their influence on multiple
traits.
• The mutation of a single gene manifests in the
alteration of several different traits.
• Diseases involving mutational pleiotropy are
characterized by deficiencies in multiple organs that
impact several body systems.

8. Selectional Pleiotropy
 focuses on the number of separate fitness
components affected by a gene mutation.
 The term fitness relates to how successful a particular
organism is at transferring its genes to the next
generation through sexual reproduction. This type of
pleiotropy is concerned only with the impact of
natural selection on traits.

9. Antagonistic Pleiotropy
1. Antagonistic Pleiotropy arises when alleles that have beneficial effects on one set of fitness
components also have deleterious effects on other fitness components.
2. Sometimes, a pleiotropic gene may be both harmful and beneficial to an organism, which is referred
to as antagonistic Pleiotropy.

10. EXAMPLES OF PLEIOTROPY

11. SICKLE CELL ANAEMIA
 Sickle cell anaemia is a genetic disease that causes deformed red blood cells with a rigid,
crescent shape instead of the normal flexible, round shape. It is caused by a change in
one nucleotide, a point mutation in the HBB gene(beta-globin gene).
 This mutation results in red blood cells that are sickle-shaped, which causes them to
clump together and become stuck in blood vessels, blocking normal blood flow.
 This results in multi-organ failure.

12. Phenylketonuria (PKU)
 An inherited disorder that increases the levels of a substance called phenylalanine in the blood.
 Phenylketonuria causes this amino acid to increase in amount in the body, which can be very
dangerous.
 PKU is caused by a mutation of the gene responsible for the production of an enzyme called
phenylalanine hydroxylase. This enzyme breaks down the amino acid phenylalanine that we get from
protein digestion.

13. MARFAN SYNDROME
 Marfan syndrome is a condition that affects the connective tissue.
 It is an autosomal dominant disorder which affects 1 in 5–10,000 people.
MFS arises from a mutation in the FBN1 gene, which encodes for the glycoprotein fibrillin-1, a major constituent of
extracellular micro fibrils which form connective tissues. Over 1,000 different mutations in FBN1 have been found to result in
abnormal function of fibrillin, which consequently relates to connective tissues elongating progressively and weakening.

14. Pigmentation and Deafness in Cats
 Approximately 40% of cats with white fur and blue eyes are deaf. An initial hint at the
link between pigmentation and deafness was the observation that white cats with one
blue eye and one yellow eye were deaf only on the blue-eyed side. Because the gene
responsible for both of these phenotypes affects pigmentation as well as the ability to
hear, the gene is pleiotropic.
The high heritability coefficients for both
traits(blue and yellow), 0.55 and 0.75
respectively, indicate that beside the
major gene there is an important
influence of polygenic effects.