About monosomy and its application

1. Monosomic analysis

2.  INTRODUCTION
 HISTORY
 CYTOLOGY
 METHODS OF PRODUCTION
 IDENTIFICTION OF MONOSOMICS
 MONOSOMIC ANALYSIS
Content:

3. INTRODUCTION:
ANEUPLOIDY:
The loss or gain of one or few chromosomes as compared to
the somatic chromosome number of a species is known as
aneuploidy.
Hyperploidy: due to gain of one or more chromosome
Hypoploidy: due to loss of one or more chromosome

4. CLASSIFICATION:

5. MONOSOMIC:
An individual lacking one chromosome from one diploid or
somatic set(2n-1) of chromosome is called monosomic.
DOUBLE MONOSOMIC:
Double monosomic lack 2 chromosome , each from two
different chromosomes(2n-1-1).

6. MONOSOMY
DOUBLE
MONOSOMY

7. OTHER TYPES OF MONOSOMICS :
Monotelosomic (20II +1I ): loss of telocentric type
chromosome.
Monoisosomic (20II +1I iso): loss of isochromosome
Tertiary monosomic(20II +1I translocated):loss of a
translocated chromosome.

9. MORPHOLOGICAL EFFECTS:
Monosomic individual forms gametes of two types (n)
and(n-1).
Number of possible monosomics in an organism will be
equal to haploid chromosome number. (Eg. In common wheat
(n=21) , 21 possible monosomics are known).

10. CONTD…
Monosomy in diploids is not tolerated, since it creates
imbalance due to loss of one complete chromosome.
however in polyploids, monosomy has apparent effect, since
they have several chromosome of same type and loss of one
chromosome can be easily tolerated.

11. HISTORY:
1916-Bridges discovered X0 male in drosophila which
had 7 chromosomes.
1920’s- scattered reports of monosomic plants in tobacco,
bread wheat, cotton, maize.
1944- E.R.clausen and D.R.cameron reported 24
monosomics for tobacco(Nicotiana tabaccum).

12. CONTD….
1954- E.R.Sears reported 21 monosomics in wheat(chinese
spring)
1963-J.Endrizzi and coworkers reported monosomics in
cotton.

13. CYTOLOGY:
One chromosome of haploid complement does not have pair,
Remains unpaired during meiosis.
Present as univalent
Bivalents disjoins normally in A-I
Single univalent may be,
(1) move to one of the two poles
(2)lag behind at metaphase plate and be ultimately lost
(3)Divide into two chromatids which move to opposite poles

14. BEHAVIOR OF UNIVALENT
CHROMOSOME DURING MEIOSIS IN
MAIZE MONOSOMIC-6 PLANT:

15. CONTD…
( a ) Univalent chromosome attached to nucleolus during
pachytene.
( b ) Univalent chromosome 6 attached to nucleolus during
diplotene.
( c ) Metaphase I showing 9II + 1I with univalent
chromosome arranged on metaphase-I plate
( d ) Metaphase I showing 9II + 1I with univalent
chromosome lies o ff metaphase-I plate
( e ) Anaphase-I showing 9 − 9 chromosome disjunction
with univalent chromosome lagging at metaphase plate.
( f ) Late anaphase-I showing equational division of
univalent chromosome and two lagging monads

16. UNIVALENT SHIFT:
When monosomic plants are crossed with normal plant during
monosomic analysis, some progeny plants are monosomics for
a different chromosomes as compared to their monosomic
parent
 due to univalent reduces synapsis between homeologous
chromosomes.so more than one univalent present in MI.
Irregular distribution of these univalent in AI and AII leads to
univalent shift.

17. METHODS OF PRODUCTION:
FromHaploids,Nullisomics,Trisomics
Backcrosses of interpecific hybrids
Partially asynaptic plants
Irradiation methods
Spontaneous production

23. Contd….

35. Contd…..