chromosomal aberations

1. Karyotype and chromosomal
aberrations

2. Karyotype
• The complete set of chromosomes possessed
by an organism .
• It is presented by the picture of metaphase
chromosomes lined up in descending order of
their sizes.
• Prepared by actively dividing cells.

3. Karyotype of human male

4. Karyotypes give info about
• No of chromosomes
• Major deletion, inversion, translocation and
duplication
• Addition or deletion of whole chromosome

5. Types of chromosomal mutations
• Three main types
1. Chromosomal rearrangemants
2. Aneuploids
3. Polyploids

6. Chromosomal rearrangements
• Arises due to alteration of structure of
chromosome
• In a way that a piece of chromosome may get
a) Duplicated
b) Deleted
c) Inverted
d) Translocated

7. Reasons for such arrangements
• Due to double stranded breaks in dna
and when these broken ends try to join together
after breaks their two possibilities
I. Either they join correctly and restore the info
II. Or they join wrongly and cause rearraned
chromosomes
• Crossing over may also be the reason

8. Duplication
• Part of chromosome is doubled

9. Formation of loop for synapsis

10. Types
Tandem displaced reversed
In which
duplicated
segment
immediately
adjacent to original
Duplicated
segment is far
away
In which the
duplicated
segment is
adjacent and
inverted

12. Deletion
A part of chromosome is lost

13. • A large deletion is easily detected
• In heterozygous for deletion loop must form in
normal chromosome form in order to align

14. Consequences of deletion
• If centromere is included in deletion the
segregation will not occur in mitosis and
meiosis and will usually be lost.
• In homozygous state it could be lethal as all
the copies of genes get lost
• In psuedodominance the recessive allele is
expressed when the wild type allele is deleted

15. Example
• Cri du chat syndrome;
In humans, a deletion on the short arm of 5
chromosome is responsible for cri-du-chat
Wolf hirschorns
Deletion on short arm of 4 chromosome

16. Inversion
• In which segment of chromosome is inverted
to 180 degree

17. Types
• Pericentric
• paracentric

18. Interesting fact
• Human chromosomes 4 differ from
chimpanzes by pericentric inversion.

19. Position effect
• expressions are altered as positions alter
• For example ,in drosophilla

20. Translocation
• Entails movement of genetic material
between non homologous chromosomes
• Not to be confused with crossing over

21. Types
• Reciprocal non reciprocal

22. • They may also cause position effect
• Neurofibromatosis is caused by translocation
in chromosome 17 . It is due to tumors of skin
and nervous system

23. Robertsonian translocation

24. Aneuploidy
• An increase or decrease in the no of individual
chromosome.
causes
It may be due to
1. Loss of chromosome due to deletion of
centromere
2. Robertsonian translocation
3. Due to non disjunction

25. Types
Nullisomy
The loss of both members of homologous
chromosome such as 2n – 2 =44

26. Monosomy
• Loss of single chromosome
• 2n – 1=45 chromosomes
• Example is that of turner syndrome

27. Trisomy
• gain of single chromosome
• Results from non disjunction of chromosomes
and leading to availability of three sets of
homologous chromosomes
• 2n + 1= 47
• Example is down syndrome, ptau and edward

28. Tetrasomy
• gain of two homologous chromosomes
• As 2n +2 = 48
Sex chromosomal aneuploidy is
better tolerated than
autosomal e. g turner n
klinefelter etc
Autosomal aneuploidy is less
tolerated as there is no dosage
compensation mechanism for
them.

30. Mosaicism
• Non disjunction during mitotic phase leads to
generation of patches in which every cell has a
chromosome abnormality and other normal
patches.
• e. g in turner syndrome

31. Polyploidy
• Represents the loss or gain of more than two
set of chromosomes such as 3n ,4n ,5n
• No animal has polyploidy except for a rat
argentina . Mostly found in invertebrates.

32. Autopolyploidy
• In which all chromosomal sets are from single
specie

33. Alloploidy
• Arises by hybridization of two species .
• Advantages of polyploidy are
• Plants with broad leaves flowers and fruit are
produced
• Wheat showing hexaploid genome has larger
seed as compaired to ancestors.

34. Methods to detect mutations
• Genetic amniocentesis can provide
information about developing fetus genetic
makeup.
• is usually done between weeks 15 and 20 of
pregnancy.
• Chorionic villus sampling (CVS) is used to
detect birth defects, genetic diseases before
birth done between 10 and 12 week.

36. Reference
• Benjamin A. Pierce - Genetics _ a conceptual
approach.