This document summarizes autopolyploidy, which is the presence of more than two genomic sets of chromosomes derived from a single species. Key points include: - Autopolyploids are produced through chromosome doubling within a species, such as through meiotic errors or chemical treatment. This results in organisms with 3, 4, 5, etc. copies of the genome. - Higher ploidy levels like triploids and tetraploids are often sterile due to challenges in chromosome pairing during meiosis. However, some plants widely used as crops are autopolyploids. - Identification of autopolyploids is based on observing multivalent chromosome pairing. Random chromosome segregation patterns

2. INTRODUCTION
• Most eukaryotic organisms are diploid (2n) for most of their
life cycles, possessing two sets of chromosomes.
• Occasionally, whole sets of chromosomes fail to separate in
meiosis or mitosis, leading to polyploidy, the presence of more
than two genomic sets of chromosomes.
• Polyploids which originated by doubling the chromosome
number of a diploid species, or a hybrid between races of the
same species, resulting in two pairs of chromosomes is called
Autopolyploid, and the condition is referred to as
Autopolyploidy.

3. • Autopolyploidy is due to accidents of meiosis or mitosis that
produce extra sets of chromosomes, all derived from a single
species.
•Autopolyploids have three(triploid), four(tetraploids),
five(pentaploids), six(hexaploids), seven(heptaploids), eight
(octaploids) or more copies of same genome.

4. • Autopolyploids are produced through chromosome
doubling of a species. chromosome doubling may occur in
somatic cells giving rise to tetraploid buds.
• In solanace 6-36percent of shoots are reported to the
tetraploids. Some chemicals such as acenapthane, 8-
hydroxy quinoline and nitrous oxide induce chromosome
doubling.
• The most efficient method of chromosome doubling is the
treatment of seeds, seedlings or shoot tips with colchicine

5. is an alkoloid extracted from the bulbs of
Colchicum autumnale.
• It has the chemical formula of C22H25O6N.
• It interferes with the development of spindle apparatus as a
consequence of which the sister chromatids of chromosomes
are unable to migrate to the opposite poles during anaphase.
Therefore, all the chromatids(=4) are included in the same
restitution nucleus leading to chromosome doubling.
• Colchicine is generally applied as 0.2% aqueous solution or
lanolin paste. The duration may vary from 3-24 hrs in the
case of seeds and seedlings.
• The chromosome doubling effect of colchicine was first
described by Blakesle and Avery, and by Nebel in 1937.

7. Occurrence of Autopolyploidy
i. Non disjunction of gametes
a. Autopolyploidy through mitosis
b. Autopolyploidy through meiosis
ii. By genome duplication

8. • Nondisjunction of all chromosomes in mitosis in an early 2n
embryo, doubles the chromosome number and produces an
autotetraploid (4n).

9.  An autotriploid (3n) may arise when nondisjunction in
meiosis produces a diploid gamete that then fuses with a
normal haploid gamete to produce a triploid zygote.
Alternatively, triploids may arise from a cross between an
autotetraploid that produces 2n gametes and a diploid that
produces 1n gametes.

10. • Because all the chromosome sets in autopolyploids are from the same
species, they are homologous and attempt to align in prophase I of meiosis,
which usually results in sterility.
 Consider meiosis in an autotriploid. In meiosis in a diploid cell, two
chromosome homologs pair and align, but, in autotriploids, three homologs
are present. One of the three homologs may fail to align with the other two,
and this unaligned chromosome will segregate randomly.
 Which gamete gets the extra chromosome will be determined by chance
and will differ for each homologous group of chromosomes. The resulting
gametes will have two copies of some chromosomes and one copy of others.
Even if all three chromosomes do align, two chromosomes must segregate to
one gamete and one chromosome to the other.
 Occasionally, the presence of a third chromosome interferes with normal
alignment, and all three chromosomes move to the same gamete.

11. In meiosis of an autotriploid, homologous chromosomes can pair or not
pair in three ways

12. • A gamete produced by meiosis in such an autotriploid might
receive, say, two copies of chromosome 1, one copy of
chromosome 2, three copies of chromosome 3, and no copies of
chromosome 4.
• When the unbalanced gamete fuses with a normal gamete
(or with another unbalanced gamete), the resulting zygote has
different numbers of the four types of chromosomes. This
difference in number creates unbalanced gene dosage in the
zygote, which is often lethal.
For this reason, triploids do not usually produce viable
offspring.

13. Plant Type of
polyploidy
Ploidy Chromosome
number
Potato Autopolyploid 4n 48
Banana Autopolyploid 3n 33
Peanut Autopolyploid 4n 40
Sweet potato Autopolyploid 6n 90
Examples of Autopolyploids

14. Autopolyploidy arises from genome duplication
species A
species A
diploid
(fertile)
X
autotetraploid
(fertile)
spontaneous
genome
duplication
Cause of genome duplication:
a) meiotic non-reduction of gametes (both in egg and sperm)

15. Genetic effects
 In many species, autopolyploids show an increase in general
vigour and size: the phenomenon is known as gaigantism.
 In general, leaves of autopolyploids are larger and thicker, and
their flowers, fruits and seeds are larger.
 Cells, pollen grains and stomata of autolpolyploids are
relatively larger than are those of diploids.
 All autopolyploids show variable sterility.
 Their growth rate is generally lower than that of normal
plants, and they are later in flowering.
 Autopolyploids have a relatively higher water content than
that of normal plants hence the fresh weight is more.

16. Cytology
 Autopolyploids are charecterized by the presence of
multivalents at MI.
 In triploids the three homologues for each chromosome form
either a trivalent or a bivalent and a univalent. During AI, the
disjunction of trivalents and the distribution of univalents is
irregular producing a range of aneuploid gametes.
 As a result, triploids produce a range of aneuploid progeny.
EX; trisomics, double trisomics etc., most of the gametes of
triploids are unbalanced and inviable as a result of which
they are highly sterile.

17.  In autotetraploids, the four homologues of each
chromosome may associate as one quadrivalent, a trivalent
and a univalent, or two bivalents at MI.
 The disjunction of trivalents and the behaviour of univalents
at AI is usually irreguar, while the quadrivalents may often
dissociate 2:2. as a result a variable proportion of the
gamates produced by the tetraploids are unbalanced and
inviable, which accounts for their variable fertility.
 The fertility of autotetraploids has been considerably
improved through selection in several species, e.g., maize,
bajra, rice etc.

18. How can we identify autopolyploids?
Autopolyploids typically have multivalent pairing
- chromosomes are more or less identical (polysomic
inheritance)

19. Role of autopolyploids in Evolution
• Autopolyploidy has contributed to a limited extenct in
evolution of plant species.some of our crops are
autopolyploids. E.g., potato(4x), peanut(4x), coffee(4x),
lucern(4X), banana(3x) and sweet potato(6x).
• Autotetraploids appear to have been more successful as
crops than other forms of autopolyploidy.
• In addition, many of forage grasses and several ornamental
species are autopolyploids.

20. Applications in crop improvement
• Triploid water melons are produced by crossing tetraploid(4x,
female) and diploid(2x male)lines.
• Triploid sugarbeets produce larger roots and more sugar per
unit area than do diploids.
• Autotetraploid cabbage and turnip are larger in size and water
content than diploids.
• In ornamental tetraploids the flowers are larger and longer
flowering duration than do diploids.
• The only autotetraploid commercial varieties are of Rye.
Examples: Double steel and Tetra petkus.

21. Triploids
 Triploids are produced by hybridization between tetraploid
and diploid strains.
 They are generally highly sterile, except in a few cases. This
feature is useful in the production of seedless watermelons. In
certain species, they may be more vigorous than the normal
diploids, e.g., in sugarbeets.
Tetraploids
 Autotetraploids have been produced in a large number of crop
species and have been extensively studied in several cases.
 Tetraploids may be useful in one of the following ways: (1) in
breeding, (2) improving quality, (3) overcoming self
incompatibility, (4) making distant crosses and (5) used
directly as varieties.
• Some autotetraploids may be superior in some quality
characters to their respective diploids, e.g., tetraploid maize
has 43% more carotenoid pigment and vitamin A activity than
the diploid.

22. Limitations of Autopolyploidy
• The larger size of autopolyploids is generally accompanied
with a higher water content. As a result, autopolyploids of
the crop species grown for vegetative parts do not always
produce more dry matter than the respective diploids.
• Triploids cannot be maintained except through clonal
propagation.
• New polyploids (raw polyploids) are always characterized
by a few or more undesirable features, e.g., poor strength of
stem in grapes, irregular fruit size in watermelons, etc. Thus
new polyploids can rarely be used directly in crop
production.

23. Chromosome segregation in autopolyploids
Possible genotypes in an autotetraploid
• AAAA Quadruplex
• AAAa Triplex
• AAaa Duplex
• Aaaa Simplex
• aaaa Nulliplex
A simplex individual has one dominant and 3 recessive
alleles(Aaaa), a duplex has 2 dominant and 2 recessive alleles
(Aaaa), while a nulliplex has none(aaaa)

24. a. Random chromosome segregation
• Segregation in a simplex (Aaaa) when the gene A is located
close to the centromere, crossing over between the
centromere and gene A would not take place.
• In this case, both the sister chromatids of each chromosomes
are attached to the same centromere and would move to the
same pole at AI.
• At AII the sister chromatids carrying the dominant alleles
would move to the opposite poles. Therefore, the two
dominant alleles do not reach the same gamete,i.e., AA gamete
is not produced. Such segregation is known as Random
chromosome segregation
Types of Chromosome segregation
a. Random chromosome segregation
b. Random chromatid assortment

25. • Chromosome segregation in in a simplex would produce two
type of gametes Aa and aa in the ratio 1:1 and genotypes
Aaaa, Aaaa and aaa in the ratio 1:2:1.
• If a single dominant allele A is able to produce phenotype. It
is assumed that at MI only quadrivalents are formed and
that separation of chromosome is random.