Download - chromosomal aberrations in number
Numerical chromosomal aberrations.
Atika Noor 1
ASSIGNMENT ON GENETICS
NUMERICAL CHROMOSOMAL ABBERATIONS
Submitted to:
Sir IMRAN BASHIR.
Submitted By:
ATIKA NOOR.
Swot Degree College Liaquat Pur.
Numerical chromosomal aberrations.
Atika Noor 3
ACKNOWLEDGEMENT
Presentation, Inspiration and motivation have
always played an important role in the success of venture.
The success and final outcome of my assignment required a
lot of guidance and assistance .I am acknowledged to indebted all my
success to my Botany teacher
“Sir IMRAN BASHIR”, who encouraged
appealed and enlighten my abilities to help me to prepare such an
excellent assignment.
At last but not the least I pay humble thanks to my college
principal, “Sir NAEEM AKHTAR.”
Atika Noor
Numerical chromosomal aberrations.
Atika Noor 4
Dedication:
Dedicated to my teacher,
With words,
Across galaxies of time &space;
Travelling just to see my goal.
Lost amidst the countless stars;
To bring me back to where you are.
And my parents who say to inspire me,
“Though you can love you cannot master, you cannot
master what you don’t love.”
Atika Noor
Numerical chromosomal aberrations.
Atika Noor 5
Table of contents:
Numerical Chromosomal Aberrations
Euploidy
Aneuploidy
Types of euploidy.
Monoploidy (1n)
Diploidy.(2n)
Polyploidy.(3n,4n,5n…)
Types of polyploidy
Autopolyploidy.(AAA) or (AAAA)
Allopolyploidy.(AABB) or (AAB)
Types of Aneuploidy.
Hypoploidy.(2n-x)
Hyperploidy.(2n+x)
Monosomy.(2n-1)
Nullisomy.(2n-2)
Trisomy.(2n+1)
Tetrasomy.(2n+2)
Numerical chromosomal aberrations.
Atika Noor 6
Numerical Chromosomal Aberrations
Introduction:
All animals and plants have a complete genome consisting of two sets of
chromosomes in somatic cell and one set in gametes .Sometimes
aberrations occur in number or structure which causes abnormality.
Change in number of chromosomes is called numerical chromosomal
aberrations. It is as well termed as ploidy. There are two kinds of ploidy.
They are as follow:
Euploidy.
Aneuploidy.
Euploidy:
The state or condition of having a variation in
chromosome number that is an exact multiple of the
characteristic haploid number.
Types: Euploidy has three types .
1) Monoploidy.
2) Diploidy.
3) Polyploidy.
Numerical chromosomal aberrations.
Atika Noor 7
Monoploidy:
The condition where each chromosome is represented only once is
called Monoploidy and the organisms having this condition are called
monoploids or haploids.
The haploids have only one set of chromosomes.
e.g. algae and fungi.
A distinction should be made between monoploids and haploid.
e.g.
In Barley=2n=x=7
Corn=2n=x=10
X= basic number.
Origin and production of monoploids:
Monoploids I some cases are found naturally and are produced
due to parthenogenesis as in male insects, bees, wasps, ants etc.
In angiosperms monoploids may also originate spontaneously due
to parthenogenetic development of eggs.
Rarely monoploids plants may originate from the pollen tube and
antipodal of the embryo sac called androgenic monoploids.
e.g. tomato and cotton under cultivation.
Artificial means of production:
1) X–ray treatment.
2) Delayed pollination.
3) Temperature shock (cold treatment)
4) Colchicines treatment.
5) Distant hybridization.
6) Anther pollen culture.
Numerical chromosomal aberrations.
Atika Noor 8
Morphology of monoploids:
Monoploids plants have reduced size of;
All vegetative parts
Flowers, seeds and stomata.
Diploidy:
The condition in which organism is called has two sets of
chromosomes is called diploidy and these organisms are called
diploid.
Explanation:
Each sexually reproducing organism has two sets of chromosomes
called homologous sets.
Thus diploid has 2n number of chromosomes.
e.g. Maize, wheat most of animals.
Polyploidy:
It is a condition in which more than two sets of chromosomes are
present, is called polyploidy and individuals are called polyploids. i.e. 3n,
4n, 5n, 6n and so on.
Three sets of chromosomes are triploids.
Four sets are tetraploids.
Six sets are called hexaploids.
Some animals such as lizards, amphibians and fish are polyploids.
Types:
a) Autopolyploidy.
b) Allopolyploidy.
Numerical chromosomal aberrations.
Atika Noor 9
Autopolyploidy:
By the addition of one or more sets of
chromosomes identical to normal haploid complement of the
same species is called autopolyploidy.
If a diploid specie has two sets of chromosomes (2n) or genome
(AA)an auto triploid has three similar sets or genome.
Tetraploids have four sets of genome.
Origin and production of autopolyploidy:
Polyploidy may arise naturally by following means;
o Due to interference with cytokinesis once replication has occurred.
o It may occur during meiosis when unreduced gametes are
produced.
o All these may occur during chilling.
Artificial methods to induce autopolyploidy are follows
o Chloral hydride.
o Mercury chloride etc.
o Radioactive substances and temperature shocks.
o Colchicines’ method.
Autotriploids arise in several ways;
1) A failure of all gametes during meiotic division may produce diploid
gametes. If such gametes are fertilized by a haploid gamete a
triploid organism is produced.
2) Two sperms may fertilize an ovum resulting triploid zygote.
3) Triploids may be produced under experimental conditions by
crossing diploid with tetraploids.
Examples:
Tomatoes.
Grapes.
Watermelon etc.
Numerical chromosomal aberrations.
Atika Noor 10
Autotetraploids:
Organisms having four sets of chromosomes are called auto
tetraploids and are produced by applying colchicines technique to cells
undergoing mitosis.
They can be produced applying heat shock proteins.
Allopolyploidy:
When the polyploidy results due to doubling of chromosome
number in a F1 hybrid which is derived from two distinctly varying
species, it is called allopolyploids. Organisms are called allopolyploids.
Explanation:
Allopolyploid has two or more genomes from two different
species. It is achieved by multiplication of chromosome sets of a hybrid
of two diploid species.
Examples:
1) A classical example of allotetraploidy in plants is the cultivated
species of American cotton (Gossipium hirsutum).this specie has
26 chromosomes, 13 large and 13 small. It was noted that old
world cotton has only 13 pairs of large chromosomes and wild
American cotton has only 13 pairs of small chromosomes.
New American cotton is tetraploid and is hybrid between old world
cotton and wild American cotton.
2) Wheat and rye example is the best example to explain the
Allopolyploidy.
Tetraploid Triticum durum (wheat),(4n=28) is crossed with diploid
Scale cereal ( rye plant),(2n=14).Triticale (6n=42) hexaploids is
obtained.
The hybrid demonstrates the characteristics of both wheat and rye.
Numerical chromosomal aberrations.
Atika Noor 11
Effects of polyploidy:
1. Morphological effects:
The polyploidy is invariably related with gigantism. The
polyploid plant has large size of;
Pollen grains.
Cells.
Leaves.
Stomata.
Xylem etc.
2. Physiological effets:
The ascorbic acid content is reported higher in tetraploid tomatoes
and cabbage.
Tetraploid maize seed has 40 %more vitamin A as compared to
diploid corn.
3. Effects on fertility:
The most important effect of polyploidy is that it produces infertility
in plants, as a result no seed formation.
4. Evolution through polyploidy:
Interspecific hybridization combined with polyploidy offers a
mechanism whereby new species may arise.
Aneuploidy:
‘’Aneuploidy may be due to loss of one or more
chromosomes or due to addition of one or more
chromosomes to the complete set of chromosomes and not
the complete set of chromosomes is involved.’’
The nuclei of aneuploids contain chromosomes whose number is not
true multiple of the basic number (n).
Types:
1) Hypoploidy.
2) Hyperploidy.
Numerical chromosomal aberrations.
Atika Noor 12
Hypoploidy:
Hypoploidy is a state in which cells contain one or more, fewer
chromosomes than what is normal.
Kinds:
a) Monosomy.
b) Nullisomy.
Monosomy:
The loss of only one chromosomes from the whole set of
chromosome is called monosomy.organisms are called monosomic
organisms.(2n-1) condition is present.
Explanation:
In animals Monosomy for one sex is common i.e. XO mechanism
in Drosophila melanogester have appearance; but is sterile male.
Loss of 4 chromosomes results in development of individual with
reduced body.
Loss of chromosome 2 or 3 is lethal.
Monosomy has been observed in maize, tobacco and datura.
A polyploid has many copies of same chromosomes so the loss of
one chromosome is easily tolerated.
Nullisomy:
Loss of a chromosome pair from the whole genome is called Nullisomy.
(2n-2) condition is present.
A nullisomy diploid often don’t survive.
In polyploids nullisomic condition survive as they have many
copies of genome.
Hyperploidy:
Having a chromosome number greater than but not an exact multiple of
the normal euploid number is called Hyperploidy.
Numerical chromosomal aberrations.
Atika Noor 13
Kinds:
a) Trisomy.
b) Tetrasomy.
Trisomy:
Trisomics are those diploid organisms which have an extra
chromosome. This condition is called Trisomy denoted by (2n+1).
Explanation:
Since the extra chromosome belongs to any of the different chromosome
of a haploid complement the number of possible Trisomics will be equal
to the haploid chromosome number, e.g. haploid chromosome number
of barley is 7 so there may 7 trisomics are possible .
Examples:
Datura trisomics ;
Haploid number of chromosome in datura is 12 and there is
12 possible trisomics.i.e.A plant with 24 chromosomes+ chromosome
no. 1 or plant with 24+an extra chromosome no. 2.
These trisomics have different shapes of capsules than normal diploids.
Drosophila trisomics:
Trisomy was discovered by Bridges in 1921.He found that
there are some female drosophila with an extra X chromosome (XXX) .
The normal drosophila male and female have XY and XX pairs of sex
chromosomes respectively.
Chromosome no. 4 of drosophila can also exist in trisomics form.
Trisomy in man:
Man has also trisomics conditions in several different chromosomes;
Down’s syndrome at chromosomes no. 21.
Patue syndrome at chromosomes no. 13.
Numerical chromosomal aberrations.
Atika Noor 14
Edward syndrome at chromosomes no. 18.
Kline filter’s syndrome is rare and is present at sex chromosomes.
Indicated by (XXY) or (XXX) females are also observed.
Tetrasomy:
The diploid organisms having two extra chromosomes are
known as tetrasomic.
Genomic formula is (2n+2).
All the 21 possible tetrasomics are available in wheat.
Numerical chromosomal aberrations.
Atika Noor 15
Referances:
Text Book of Botany.
Notes for B.Sc. by “Sir Imran Bashir.”
Notes for B.Sc. by “Sir Azad Ali Mirza.”
Genetics search on “Google”.
Genetics: Analysis and Principles by Robert Brooker.