For students studying genetics as a subject.

1.  Ploidy
 Heteroploidy
 Types of heteroploidy
 Euploidy- it’s definition, types with sub-
types, examples and origin
 Change in ploidy- types and causes.
SAKSHI

2. Ploidy :
The number of sets of chromosomes in a cell, or
in the cells of an organism.
For eg. In human there are 46 chromosomes i.e. 23
pairs of chromosomes.
There are 2 sets of chromosomes so we are having
a di ploidy or we can say we are diploid organisms.
So a ploidy shows the no. of sets of
chromosomes in a organism.

3.  Hetero is a Greek word which means
“different ” or “other”.
 So the literal meaning of heteroploidy is “a
set of chromosomes having different
chromosome number than the normal set of
it has”.
 Having an abnormal chromosome number
that deviates from the normal diploid
number of a given species is called as
heteroploidy.

5.  Euploidy is the state of a cell or organism having one
or more than one set of the same set of
chromosomes, possibly excluding the sex-
determining chromosomes.
 For example, most human cells have 2 of each of the
23 homologous monoploid chromosomes, for a total
of 46 chromosomes. A human cell with an extra set
out of the 23 normal ones would be considered
euploid.
 Euploid karyotypes would consequentially be a
multiple of the haploid number, which in humans is
23. a single extra chromosome (such as Down
syndrome).
 karyotypes are given names with the suffix-ploidy,
used for euploid karyotypes).

7.  The nucleus of a eukaryotic cell is haploid if it
has a single set of chromosomes, each one
not being part of a pair.
 By extension a cell may be called haploid if
its nucleus is haploid, and an organism may
be called haploid if its body cells (somatic
cells) are haploid.
 The number of chromosomes in a single set
is called the haploid number, given the
symbol n.

8. Haploids can be artificially produced by
any one of the following methods:
(i) X-rays treatment,
(ii) delayed pollination,
(iii) temperature shocks,
(iv) colchicine treatment,
(v) distant (interspecific or intergeneric)
hybridization,
(vi) anther or pollen culture.

9. Haploids in some cases as in male insects
(Hymenoptera) are found as a routine and are produced
due to parthenogenesis. In these insects, queen and
drones are diploid females.
Haploids may also originate spontaneously due to
parthenogenetic development of egg in flowering
plants. Such rare haploids have actually been obtained
in tomatoes and cotton under cultivation.
Rarely haploids may originate from pollen tube rather
than form egg, synergids or antipodals of embryo sac.
These haploids will be called androgenic haploids.

10.  The state of being diploid, that is having two sets
of the chromosomes (and therefore two copies
of genes), especially in somatic cells.
 Word DIPLOID is originated from Greek diplous,
which means “double”.
 For example: a human somatic cell is in diploid
state since it contains 46 chromosomes (in
contrast to the sex cell that contains only
23 chromosomes). The
46 chromosomes in somatic cell results from the
presence of two sets of chromosomes – one set
derived from the father and another set from the
mother (during the zygote stage).


12.  Polyploid cells and organisms are those containing
more than two paired (homologous) sets
of chromosomes.
 polyploidy is found in some organisms and is
especially common in plants. In addition, polyploidy
occurs in some tissues of animals that are otherwise
diploid, such as human muscle tissues.
 For e.g. Highly differentiated human tissues in the
liver, heart muscle and bone marrow. It occurs in the
somatic cells of some animals, such
as goldfish, salmon, and salamanders, but is
especially common among ferns and
flowering plants (see Hibiscus rosa-sinensis),
including both wild and cultivated species.

16. An aneuploid is an individual organism whose
chromosome number differs from the wild type by part
of a chromosome set.
Generally, the aneuploid chromosome set differs from
wild type by only one or a small number of
chromosomes.
Aneuploids can have a chromosome number either
greater or smaller than that of the wild type.
Aneuploid nomenclature is based on the number of
copies of the specific chromosome in the aneuploid
state.
For example, the aneuploid condition 2n−1 is
called monosomic (meaning “one chromosome”)
because only one copy of some specific chromosome is
present instead of the usual two found in
its diploid progenitor. The aneuploid 2n+1 is
called trisomic,2n−2 is nullisomic, and n+1 is disomic.

18.  Monosomy is a form of aneuploidy with the presence
of only one chromosome from a pair. Partial
monosomy occurs when only a portion of the
chromosome has one copy, while the rest has two
copies.
 Monosomic chromosome complements are generally
deleterious for two main reasons. First, the missing
chromosome perturbs the overall gene balance in
the chromosome set. (We encountered this effect
earlier). Second, having a chromosome missing allows
any deleterious recessive allele on the single
chromosome to be hemizygous and thus to be
directly expressed phenotypically. Notice that these
are the same effects produced by deletions.

19. Turner syndrome
 – People with Turner syndrome typically have
one X chromosome instead of the usual two
sex chromosomes. Turner syndrome is the
only full monosomy that is seen in humans—
all other cases of full monosomy are lethal
and the individual will not survive
development.

20.  1p36 deletion syndrome
 – a partial monosomy caused by a deletion at
the end of the short p arm of chromosome 1
 Cri du chat syndrome
 – (French for "cry of the cat" after the
distinctive noise by affected persons'
malformed larynx) a partial monosomy
caused by a deletion of the end of the short p
(from the word petit, French for "small") arm
of chromosome 5

21.  Nullisomic is a genetic condition involving the
lack of both the normal chromosomal pairs for
a species (2n-2). Humans with this condition will
not survive.
 Causes
 Nullisomy is caused by non-disjunction during
meiosis that causes two of the gametes to have
no chromosomal material, leaving the other two
gametes to have double the amount of
chromosomal material (disomic). Due to the lack
of genetic information, the nullisomic gametes
are rendered unviable for fertilization.

22.  A trisomy is a type of polysomy in which
there are three instances of a
particular chromosome, instead of the normal
two.
 If the chromosome pairs fail to separate
properly during cell division, the egg or
sperm may end up with a second copy of one
of the chromosomes(non-disjunction). If such
a gamete results in fertilization and an
embryo, the resulting embryo may also have
an entire copy of the extra chromosome.

23.  The most common types of autosomal trisomy that survive to birth in
humans are:
 Trisomy 21 (Down syndrome)
 Trisomy 18 (Edwards syndrome)
 Trisomy 13 (Patau syndrome)
 Trisomy 9
 Trisomy 8 (Warkany syndrome 2)
 Trisomy 22
 Of these, Trisomy 21 and Trisomy 18 are the most common. In rare
cases, a fetus with Trisomy 13 can survive, giving rise to Patau
syndrome. Autosomal trisomy can be associated with birth
defects, intellectual disability and shortened life expectancy.
 Trisomy of sex chromosomes can also occur and include:
 XXX (Triple X syndrome)
 XXY (Klinefelter syndrome)
 XYY

24.  A tetrasomy is a form of aneuploidy with the
presence of four copies, instead of the normal
two, of a particular chromosome.
 Causes
 Full tetrasomy of an individual occurs due
to non-disjunction when the cells are
dividing (meiosis I or II) to form egg and sperm
cells (gametogenesis). This can result in
extra chromosomes in a sperm or egg cell.
 For e.g. After fertilization, in human the resulting
fetus has 48 chromosomes instead of the typical
46.

25.  Autosomal tetrasomies
 Cat eye syndrome where tetrasomy of
chromosome 22 is present
 Pallister-Killian syndrome (tetrasomy 12p)
 Tetrasomy 9p
 Tetrasomy 18p
 Sex-chromosome tetrasomies
 48, XXXX syndrome
 48, XXYY syndrome
 Klinefelter's syndrome, where XXXY tetrasomy is
present