Wednesday, January 26, 2011

Chromosome Abberations

Please consider this is a note from a lecture and can have errors in spellings and where I fell asleep
Therefore anything wrong below is not to do with the lecturer but due to my laziness and neglect

Changes in the DNA at chromosome level are Chromosome aberrations / Chromosome mutations.
Changes at gene level are point mutations/gene mutations.
Chromosome mutations also get transmitted to offspring according to Mendal's laws. Chromosome aberrations include;
-Changes in the chromosome number
-Changes in the chromosome structure

Chromosome number variations
- Any departure from the normal chromosome number is called heteroploidy.
Two types

1) Aneuploidy

-An organism has gained or lost one or more chromosomes but not a complete set.
2n plus/minus chromosomes
Common conditions
2n-1 Monosomic
2n+1 trisomic
2n-2 nullisomic
2n+2 tetrasomic

2) Euploidy

-Organism in which complete haploid sets of chromosomes are found
deploid ->2n  , Normal state
poliploid -> more than 2n
  -triploid , 3n
  -tetraploid, 4n

Aneuploid in humans - Observed from karyotypes
Micrograph of chromosomes>>> Photograph it>>>Arrange and analyse to identify

Sex chromosome Aberrations

1) Klinefelter Syndrome (47) XXY - Trisomic ; complex - (48) XXXY, XXYY

2) Turner Syndrome (45) X - Trisomic

3) XXX Syndrome (47) XXX - Trisomic

4) XYY Condition (47) - Trisomy

Chromosome number aberrations - Human autosome
Downs Syndrome (47) - Trisomy,21
 Usually due to none-disjunction of the 21st chromosome pair during meiosis.

Trisomy has 3 doses of a given chromosome. The three chromosomes may form a trivalant association during meiosis. Association is not present over the entire length, because of this it upsets the meiosis balance.

Polyploidy

Common in plants and rare in animals.
1) Autopolyploidy - Extra chromosome sets are identical to the normal haploid set of the species
2) Allopolyploidy - Additional chromosome sets originates from different species

Origin of Autopoliploidy

In nature unreduced gametes may form if paired chromosomes fail to separate during meiosis. Both sets of chromosomes get incorporated in the restitution nucleus.
Autopoliploid plants are larger than their deploid relatives.
Shows a reduction its fertility.
Commercially important autopoliploids : Banana, Melon, Strawberry

Origin of Allopoliploidy

Results from hybridization between two closely related species.
Sterile due to absence of homology between chromosomes of the two species.

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