Understanding Ploidy, Types, and related
Dr. Ishan Y. Pandya
PhD, M.Sc., M.B.A. Biotechnology
Gujarat Ecological Education and Research (GEER)
Gandhinagar, Gujarat, India
The Abc of genetics..
• We are diploid organisms with two sets of
homologous chromosomes,but we contain haploid
sex cells also with one set and half the number.
• Genetics is a rife with potentially confusing scientific
terminologies associated with chromosomes,
chromosome number ,what is ploidy, which cells are
haploid, which are diploid, what are homologous
• most of the cells in the body are somatic ,or
non sex-cells and have a diploid (2n)
chromosome number.diploid means that the
chromosomes in pair and are called
homologues.every somatic cell in your body
has 46 chromosomes, half from each parent.
• Most but not all the cells in the body are
diploid.sex cells also called gametes have half
the number of chromosomes as do the
• These gametes are reffered to as being
• Ploidy refers to the number of basic
• Say for eg. A diploid has 2 sets where as a
hexaploid has 6 sets.
• The basic chromosome number x,also called
the monoploid number is the number of
different chromosomes that make up a single
Ploidy , mitosis and meiosis
• Mitosis : equational division
takes place in somatic cells
• Meiosis: reductional division
takes place in vegetative cells
Ploidy can be Further divided into two groups
based on the type of change in the
Euploidy : The condition of an organism having
complete set of chromosomes or
multiples of the basic set is euploidy
and the cell is said to be euploid.
Aneuploidy: This is a condition where the
chromosome number is not an
exact multiple of the normal diploid
number, with either
fewer or more than the normal
number of chromosome in the cell.
Monoploidy Polyploidy hypoploidy hyperploidy
Only in plants
• The condition of an organism having complete
set of chromosomes or multiples of the basic
set is euploidy and the cell is said to be
Euploidy is lethal in most animal species,
but often tolerated in plants, where it
has played a role in speciation and
Monoploidy and polyploidy involve
complete sets of chromosomes, and so
both are cases of euploidy.
Variations in number of complete chromosome sets.
Causes of occurrence of monoploidy and
Monoploidy and polyploidy can result when
either round of meiotic division lacks
cytokinesis, or when meiotic
nondisjunction occurs for all
a. Complete nondisjunction at meiosis I will
produce 1⁄2 gametes with normal
chromosomes, 1⁄2 with no chromosomes.
b. A gamete with two sets of chromosomes
fused with a normal gamete produces a
triploid (3N) zygote.
c. Fusion of two gametes that each have two
sets of chromosomes produces a tetraploid
d. Polyploidy of somatic cells can result from
mitotic nondisjunction of complete
• An individual that contains one half the
normal number of chromosomes is a
monoploid and exhibits monoploidy.
• Some species such as bees, ants and male
bees are normally monoploid because they
develop from unfertilized eggs. Consequently,
these individuals will be sterile.
• Monoploids are very rare in nature because
recessive lethal mutations become unmasked,
and thus they die before they are detected.
• These alleles normally are not a problem in
diploids because their effects are masked by
dominant alleles in the genome.
• A stage in the life cycle of some fungal species
can also be monoploid.
• Monoploidy has been applied in plant
biotechnology to rapidly develop plants from
anthers that have a fixed genotype.
Plant experiments often use monoploids.
i. Haploid cells are isolated from plant anthers and
grown into monoploid cultures.
ii. Colchicine (which inhibits mitotic spindle formation)
allows chromosome number to double, producing
completely homozygous diploid breeding lines.
iii. Mutant genes are easily identified in monoploid
Production of monoploid plants from diploid.
• Polyploidy occurs in cells and organisms when
there are more than two homologous sets of
• Very common in plants
– associated with origin of new species
– may positively correlate to size of individual.
– There are two classes of polyploids based on the
number of chromosome sets:
• . Even-number polyploids are more likely to be at
least partially fertile, because the potential exists for
equal segregation of homologs during meiosis.
• . Odd-number polyploids will always have unpaired
chromosomes. Balanced gametes are rare and these
organisms are usually sterile or have increased zygote
Triploids, pentaploids (all with odd number of chromosome sets) are
often sterile due to pairing problems during meiosis...
Even numbers of chromosomes in polyploids may lead to more normal
segregation and partitioning of chromosome sets...
• Polyploid types are labelled according to the
number of chromosome sets in the nucleus:
• triploid (three sets; 3x),
for example the phylum Tardigrada
• tetraploid (four sets; 4x), for example
• pentaploid (five sets; 5x)
• hexaploid (six sets; 6x), for example wheat
• oktoploid (eight sets; 8x), for example
Acipenser (genus of sturgeon fish)
• dekaploid (ten sets; 10x), for example certain
• dodecaploid (twelve sets; 12x), for example
the plant Celosia argentea
• The occurrence of polyploidy is a mechanism of
• Polyploid animals are often sterile, so they often
reproduce by parthenogenesis.
• Polyploid salamanders and lizards are also quite
common and parthenogenetic.
• While mammalian liver cells are polyploid, rare
instances of polyploid mammals are known, but
most often result in prenatal death.
• Plants are generally bigger in strature.
• The plants are specially sterile when if they
have odd numbered chromosome set.
• Polyploidy tolerated in plants because of
self-fertilization; plays an important role in
plant speciation and diversification.
Polyploidy in Animals?
(lethal in humans)
Some amphibians (sexual cycle)
Some salamanders, four-legged reptile
Some fish (salmonids have 2X DNA of related fish)
Triploid oysters developed - sterile
Reproduce by parthenogenesis (special
type of unfertilized egg develops into embryo)
• Polyploidy occurs in two types in plants.
Types of polyploidy in plants..
Additional sets identical to parents Hybridization of closely related species; often sterile
Autopolyploids results when all
sets of chromosomes are from
the same species, usually due to
Can arise spontaneously through
nondisjunction of a whole chromosome set.
• Triploids commonly made by crossing diploids
2n X 4n = 3n progeny (many seedless
• Tetraploids can be induced by treatment with
• Examples include:
like bananas (3n =
33), grapes and
– (2) Grasses,
crop plants and
– hybrid of two or more closely related species
– partially homologous chromosomes
Allopolyploidy is caused by the presence of
several genomes of different species in a cell, a
tissue or a whole organism.
• For example:
– (1) Fusion of haploid gametes from species 1 and
species 2 produces an N1 + N2 hybrid plant. No
chromosomal pairing occurs at meiosis, viable gametes
are not produced and the plants are sterile.
– (2) Rarely, division error or cold shock doubles
the chromosome sets (2 N1 + 2N2). The diploid sets
function normally in meiosis, and fertile allotetraploid
– (3) An example is crosses between cabbages
(Brassica oleracea) and radishes (Raphanus sativus),
which both have a chromosome number of 18.
If pairing partners can be provided for homologs in
allopolyploids, sterility can be relieved…e.g. Karpechenko (1928)
Amphidiploids = nonidentical chromosome sets doubled in
(n) = 18
Monoploid number (x) = 9
Chromosome sets unpaired
Polyploidy is the rule in agriculture,
where polyploids include all commercial
grains (e.g., bread wheat, Triticum
aestivum (2n = 42), an allohexaploid of
three plant species), most crops and
• A mosaic or mosaicism denotes the presence
of two populations of cells with different
genotypes in one individual, who has
developed from a single fertilized egg.
• Mosaicism may result from a mutation during
development which is propagated to only a
subset of the adult cells.
• The most common form of mosaicism found through
prenatal diagnosis involves trisomies.
• Although most forms of trisomy are due to problems
in meiosis and affect all cells of the organism, there
are cases where the trisomy only occurs in a
selection of the cells.
• This may be caused by a nondisjunction event in an
early mitosis, resulting in a loss of a chromosome
from some trisomic cells.
• An example of this is one of the milder forms
of Klinefelter's syndrome, called 46/47 XY/XXY
mosaic wherein some of the patient's cells
contain XY chromosomes, and some contain
• The 46/47 annotation indicates that the XY
cells have the normal number of 46 total
chromosomes, and the XXY cells have 47 total
A mosaic fruit fly- Bilateral Gyandromorph
(both Male and Female Genotypes)
Female (XX) half:
heterozygous for both
Male (XO) half:
Occurs from loss of one X (with wildtype alleles) at
1st mitotic division during development, oriented
• A Robertsonian translocation is a type of in which
two nonhomologous acrocentric chromosomes
(chromosomes that are not members of the same
pair and have centromeres near their ends) break at
• The long arms may become attached to a single
centromere and serve a function. The short arms
also join to form a reciprocal product, which typically
contains nonessential genes and is usually lost within
a few cell divisions.
• In humans, when a Robertsonian translocation joins
the long arm of chromosome 21 with the long arm of
chromosome 14 (or 15), the heterozygous carrier is
phenotypically normal because there are two copies
of all major chromosome arms and hence two copies
of all essential genes.
• However, the progeny of this carrier may inherit an
unbalanced trisomy 21, causing Down Syndrome.
• About one in a thousand newborns has a
• The most frequent forms of Robertsonian
translocations are between chromosomes 13
and 14, 13 and 21, and 21 and 22
• In several forms, Robertsonian translocations
cause chromosomal deletions or addition and
result in syndromes of multiple
malformations, including trisomy 13 (
Patau syndrome) and trisomy 21 (
• Disjunction refers to the normal seperation of
homologous chromosomes or chromatids to
opposite poles at nuclear division.
• Non disjunction refers to the failure of normal
seperation of homologous chromosomes or
chromatids to opposite poles at nuclear
• There are two possibilities mainly for the
disjunction to fail:
Non Disjunction at Meiosis I is more common
than Meiosis II.
• Microtubule inhibitors cause non-disjunction.
• Formation of tetrad is critical for correct
disjunction since disomic gametes are usually
• Mutations that interfere with recombination
increase the frequency of meiosis I non-
• In diploid organisms aneuploid variations take
four main forms that can be classified under
two main groups:
• Hypoploidy: loss of one or more
chromosomes from basic
• Hyperploidy: presence of one or more
chromosomes in the basic
Normal (theoretical) set of metaphase chromosomes in a diploid
(2N) organism (top) and examples of aneuploidy (bottom)
• It’s a form of aneuploidy with the presence of only
one chromosome (instead of a pair in humans)from a
• A monosomic cell hence involves a loss of a single
chromosome that is the cell is 2n-1.
• Partial monosomy occurs when only a portion of the
chromosome has one copy while the rest has 2
• This condition mainly occurs due to the non
disjunction in meiosis in parent producing a
gamete with no copies of a particular
chromosome and one copy of all other
chromosomes in the set.
• The number of possible monosomics in an
organism is equal to its chromosome number.
• Monosomy is usually not tolerated in diploids
but can be easily introduced in
polyploids,however several experiments have
been carried out and certain degree of success
has been observed.
• Usually autosomal lethal due to dosage
• Turner Syndrome
• Cri du chat syndrome
• Turner syndrome or Ullrich-Turner syndrome
encompasses several conditions, of which
monosomy X is the most common.
• It occurs in about 1 out of every 2500 female
births.Instead of the normal XX sex
chromosomes for a female, (or XY for a
normal male) only one X chromosome is
present and fully functional.
• In rarer cases a second X chromosome is present but
abnormal, while others with the condition have
some cells with a second X and other cells without it
• A normal female karyotype is labeled 46,XX;
individuals with Turner syndrome are 45,X. In Turner
syndrome, female sexual characteristics are present
but generally underdeveloped
• The syndrome is named after Henry Turner,
an Oklahoma endocrinologist, who described
it in 1938.
• In Europe, it is often called Ullrich-Turner
syndrome or even Bonnevie-Ullrich-Turner
syndrome to acknowledge that earlier cases
had also been described by European doctors.
• Short stature
• Lymphedema (swelling) of the hands and feet
• Broad chest (shield chest) and widely-spaced
• Low hairline
• Low-set ears
• Reproductive sterility
Approximately 98% of all fetuses with Turner
syndrome result in miscarriage.
• Turner syndrome accounts for about 10% of
the total number of spontaneous abortions in
the United States.
• The incidence of Turner syndrome in live
female births is believed to be 1 in 2500
• Turner syndrome may be diagnosed by amniocentesis during
• Sometimes, fetuses with Turner syndrome are identified by
abnormal ultrasound findings (i.e. heart defect, kidney
• Although the recurrence risk is not increased, genetic
counseling is often recommended for families who have had a
pregnancy or child with Turner syndrome.
• A blood test, called a karyotype, analyzes the chromosomal
composition of the individual. This is the test of choice to
diagnose Turner syndrome.
Cri du chat syndrome
• Cri du Chat syndrome or Cri-du-Chat
syndrome (French for Cry or call of the cat
referring to the specific cry of the child), also
called deletion 5p syndrome, 5p minus or
Lejeune’s syndrome, is a rare genetic disorder
due to a missing portion of chromosome 5.
• It was first described by Jérôme Lejeune in
• The condition affects an estimated 1 in 20,000
to 50,000 live births.
• The disorder is found in people of all ethnic
backgrounds and is more common in females
by a 3-1 ratio
• The syndrome gets its name from the
characteristic cry of infants born with the
• The infant sounds just like a meowing kitten,
due to problems with the larynx and nervous
• This cry identifies the syndrome
• Diagnosis is based on the distinctive cry and
accompanying physical problems.
• Genetic counseling and genetic testing may
be offered to families with individuals who
have cri du chat syndrome.
Mental retardation, abnormal development of glottis and larynx
1 / 50,000 live births
Cri-du-chat Syndrome (46, -5p)
A case of double monosomy
• Double monosomy mosaicism was reprted in
a retarded child with multiple congenital
• Double monosomy mosaicism was observed
in a three-year-old girl who had mental and
Routine blood-lymphocyte and bone-marrow
chromosome studies showed an apparent 45,
X pattern, which was confirmed by
autoradiographic studies with tritiated
• Routine and fluorescent chromosome
analyses from bilateral skin biopsies revealed
a 45,XX,21- karyotype, which was consistent.
• Although her clinical features bore some
resemblance to patients with Turner's
syndrome, the patient did not closely fit either
of these syndromes
• Involves loss of one homologous chromosome pair
that is the cell is 2N-2.
• Its lethal in diploids.
• Can be tolerated in bread wheat
- it’s a hexaploid
- behaves meiotically like a diploid
- 4 homologous chromosomes
compensate for missing pair of homologs
Sears isolated 21 nullisomics in wheat
• Mainly due to non disjunction occuring for the
same chromosome in meiosis in both parents
producing gamete each with no copies that
chromosome and one copy of all other
chromosomes in the set.
Neuronal migration defect in BRCA1 gene
• A BRCA1 5382insC mutation was identified in
a family with multiple cases of breast and
ovarian cancer and eastern European
• Predictive genetic testing was offered to all
family members after standard genetic
counselling within the regional clinical
a case of a possible nullisomy.
From the diaries…
• chromosomal abnormalities in sperm from
resulted in the detection of double aneuploidy
(double monosomic and double nullisomic
conditions)using in situ hybridization using
one probe set.
• A chromosomal anomaly that is characterized by
presence of an extra chromosome in the cells of a
person or a plant body.
• A trisomic cell involves an extra chromosome that is,
the cell has three copies of one chromosome type
and two copies of every other chromosome type.
• A trisomic cell is 2N+1.
• A partial trisomy occurs when part of an extra
chromosome as opposed to a whole extra
• Trisomies are viable. several can live to
adulthood ,are fertile and can produce viable
Examples of most common trisomic
• Trisomy 21 : Down Syndrome
• Trisomy 18 : Edward’s Syndrome
• Trisomy 13 : Patau’s Syndrome
• In trisomy 21, the presence of an extra set of genes
leads to over expression of the involved genes,
leading to increased production of certain products.
• For most genes, their over expression has little effect
due to the body's regulating mechanisms of genes
and their products. But the genes that cause Down
syndrome appear to be exceptions.
A few genes in …..
• COL6A1 -- overexpression may be the cause of heart defects
• ETS2 -- overexpression may be the cause of skeletal
• CAF1A -- overexpression may be detrimental to DNA synthesis
• Cystathione Beta Synthase (CBS) -- overexpression may
disrupt metabolism and DNA repair
• DYRK -- overexpression may be the cause of mental
• CRYA1 -- overexpression may be the cause of cataracts
• One of the more notable aspects of Down syndrome
is the wide variety of features and characteristics of
people with trisomy 21.
• There is a wide range of mental retardation and
developmental delay noted among children with
Down syndrome. Some babies are born with heart
defects and others aren't.
• Because of the small size of the 21st chromosome
and its association with Down syndrome, it is a
heavily mapped human chromosome.
• Research is focusing on trying to identify genes and
their effects when overexpressed.
• Trisomy 18 is the second most common
trisomy and occurs when a baby has three of
the eighteenth chromosome.
• This results in 47 chromosomes instead of the
normal 46 in the affected cells. It is this extra
genetic material that causes the problems
associated with Trisomy 18.
• Trisomy 18 is also called Edwards syndrome (or
Edward's syndrome) and occurs in about 1:3000 live
• Unlike Down syndrome, Trisomy 18 is usually fatal,
with most of the babies dying before birth and
those who do make it to birth typically living only a
• However, a small number of babies (<10%) live at
least one year.
Some of the typical characteristics of Trisomy 18 can include heart defects
• VSD (Ventricular Septal Defect )- a hole between the lower chambers of
• ASD (Atrial Septal Defect) - a hole between the upper chambers of the
• coarctation of the aorta (a narrowing of the exit vessel from the heart)
• kidney abnormalities
• omphalocele (a portion of the intestinal tract is located outside the
stomach in a sac)
• The syndrome or trisomy 13 is the least common
trisomic condition observed.It is a full trisomic
• In this disorder three copies of chromosome 13 are
present thereby bringing about a diseased condition.
• The occurrence of the disorder is 1 in 5000 live
The symptoms include
• facial defect
• Characteristic facial features
• Retarded growth
• Poorly developed sexual characters
• The condition of a tetrasomic cell involves an
extra chromosome pair resulting in the
presence of four copies of one chromosome
and two copies of every other chromosome
• A tetrasomic cell is hence 2N+2.
• This could arise if non disjunction occurs for
the same chromosome in meiosis in both
parents producing gamete each with two
copies of that chromosome and one copy of
all other chromosomes in the set.
• We have a condition of a double tetrasomy
with a cell with 2N+2+2 that has two
chromosomes present in four copies each.
• A disorder associated with tetrasomic
condition in humans is the klinefelter’s
• Klinefelter's syndrome, 47,XXY or XXY
syndrome is a condition caused by a
chromosome aneuploidy. Affected individuals
have at least two X chromosomes and at least
one Y chromosome.
• The principal effects are development of small
testicles and reduced fertility.
• A variety of other physical and behavioral
differences and problems are common, though
severity varies and many boys and men with the
condition have few detectable symptoms.
• Affected males are almost always effectively sterile,
although advanced reproductive assistance is
• Some degree of language learning impairment may
be present,and neuropsychological testing often
reveals deficits in executive functions.
• In adults, possible characteristics vary widely and
include little to no signs of affectedness, a lanky,
youthful build and facial appearance, or a rounded
body type with some degree of gynecomastia
(increased breast tissue).
• The second most common extra chromosome
condition, it is named after Dr. Harry Klinefelter, an
endocrinologist at Massachusetts General Hospital,
Boston, Massachusetts, who first described it in
• The condition exists in roughly 1 out of every 500
• Double autosomal tetraploidy is very rare in
live births as well as abortuses.
• But a case of an abortus with 48
chromosomes with 2 extra chromosomes
was reported with double trisomy or
• The studies reveal that the anomaly might
have occurred during the parental
• This may have arisen due to non disjunction at
both the meiotic stages or a double non
disjunction during the first meiotic division
possibly during oogenesis if we assume that
the spermatozoa with a disomy or trisomy is
• This was a rare observation marking by
professor Dhadial from the paediatric
research unit Guy’s hospital and medical
• From the knowledge gained by far we can analyze
the cituation and predict the role of ploidy in the
evolutionary processes that have been undergoing
and the ones that are.
• One of the major roles played by the ploidy can be
clearly visualised in the evolution,plant
speciation,generation and production of better
varities of plants,crops,seeds and other products.
And the journey continues…..
• We can efficiently study and monitor the species
interrelationships and evolutionary characteristics in major
• It is now possible to get a clear idea of the genetic make up of
• With this one can correlate the changes observed with the
evolutionary evidences to correlate evolutionary
conservativeness, breakpoints and trace the path of
• And the story continues…….
• I genetics – Peter russel
• The american naturalist- vol 74 G.Ledyard
• Botany online – classical genetics
• The journal of medical genetics online
• Trisomy 18 foundation
• Lecture series- university of california
• Molecular genetics disease mechanism- R.Daniel
• Nature periodicals
• Ploidy – Tami port
• KARGER-cytogenetic and genomic research.
• Journal of medical genetics
• The story of the down syndrome – len leshin
• Rainbows down under foundation
Human intelligence is divergent evolution………..