mutation and plasmid for medical laboratory

Medical laboratory

1. Mutation

2. Outline
Types of mutation
Mutagenic agents
How mutation affects the genetic code?
Repair of Mutation
Mutant isolation & detection

3. 3
Introduction
Mutation is a permanent change in the
sequence of nucleotides in DNA
Passed to all daughter cells (inherited)

4. 4
Types of Genetic Variants
Single gene mutation
Chromosomal mutation

5. Single gene mutation
Mutation that affect only a single gene
due to changes in a nucleotide sequence
Not microscopically observable
Centers on changes in coding DNA or in
the regulatory sequences, changes in the
other parts usually have no clinical
consequences

6. Types of single gene mutation
1. Point mutation -base pair substitution
it is mutation in which one bpis replaced
by another
replacement of one nucleotide by
another may or may not affect amino
acid sequence
consists of: silent & non-silent

7. 7
Types of Point mutation
a. Silent mutation
onew codon still codes for same amino acid,
because of redundancy of genetic code,
b. Non-silent mutation: involves
Mis-sense mutation:
None sense mutation:

8. 8
Types of non-silent
Mis-sense mutation:
-codon changed such that it encodes a
new amino acid
-E.g. sickle cell anemia: glutamic acid
(normal) changed to valin (abnormal)

9. None sense mutation
codon changed to stop codon; causes
early chain termination in mRNA
resulting Incomplete (nonsense protein
chain) (inactive products).
Conversely. If the stop codon is altered
it encodes an abnormally elongated
polypeptide can

10. 10
2 Frame shift mutation
Addition or deletion of one or more base
pairs
This adding or deleting a single bp, change
the reading frame of the transcribed mRNA
Result in frame-shift mutations, & different
polypeptides being made, usually
nonfunctional

11. 11

12. 12
Chromosomal mutation
1.Chromosome number abnormality
Each organism has a typical number of
chromosomes
Each organism has a typical number of sets
of chromosomes

13. Chromosome number abnormality
A. Euploidy:
the chromosome number is a multiple of
the haploid set (23 chromosomes) &
termed as euploid (Greek, eu = good &
ploid = set)
E.g. Haploid gametes & diploid somatic
cells

14. 14
B. Aneuploidy
Cells that do not contain a multiple of 23
chromosomes are termed aneuploid.
missedor additionalchromosomes is
usually one but it is possible more than
one.
Causes: Non-disjunction

15. 15
Types of Aneuploidy
1.Monosomy:
Presence of only one copy of
chromosomes in diploid cells
E.g. Turner syndrome

16. Types of aneuploidy
2. Trisomy:
The presence of three copies of
homologous chromosomes.
Less sever than mosomies because
body can tolerate excess genetic
materials than deficit
E.g. trisomy 21, trisomy 18, trisomy 13,
klinefelter syndrome.

17. 17
Autosomalaneuploidy
It is the most clinically important of the
chromosomes abnormalities
Cause: Non-disjunction:

18. 18
1. Trisomy 21
Down syndrome (described in 1866 by
John Langdon Down)
1 /700 children affected & compatible
with survival to term
It is due to an extra copy of chromosome
21
correlated with age of mother
karyotyping, 47, xx, + 21 or 47, xy, +21

19. 19

20. 20
2. Trisomy 18
Edward syndrome
second most common abnormalities
Occurs 1/6,000 birth
karyotyping, 47, xy, +18 or 47, xx, +18

21. 21
3. Trisomy13
Patau syndrome
Kayotyping 47,xy, +13 or 47, xx, +13
1/500 –10,000;
Rarely survive more than a year.

22. 22
Sex chromosome aneuploidy
1. Monosomy of the X chromosome (X
females)
occur 1/400males & 1/650female live birth
infants with some form of sex chromosome
aneuploidy.
Associated with a single X chromosome (45, x)
Turner’s syndrome: Described by Henry Turner in
1938
Phenotypically female but sex organs do not
mature & are sterile

23. 23
oCause of X females:
Deletion of some or the entire short arm
of X chromosome (10 –20 %)
Absence of paternallyderived x
chromosomes i.e. the offspring receives
an x chromosome only from her mother

24. 24
2. TrisomyX: XXX females
47, xxx
1/1000 live births;
Suffer from sterility& menstrual
irregularity
Cause: non-disjunction in the mother

25. 25
3. Klinefelterssyndrome: XXY males
Described by Harry Klinefelter in 1942
Associated with 47, xxy karyotype & 48, xxxy
& 49, xxxxy have also be recorded.
1/2000-1,000 live births;
have male sex organs, but are abnormally
small;
breast enlargement & other female
characteristics; breast dev’t is seen in 1/3rd of
the affected males & leads to an increased
risk of breast cancer

26. 26
4. 47, xyysyndrome: XYY males
Karyotye is 47, xyy
taller than average
Involves a slight degree of IQ reduction but
few physical problems
Cause: Non-disjunction in the father

27. 27
C. Polyploidy: extra chromosome sets
Presence of a complete set of extra
chromosomes
Include:
triploidy &
tetraploidy

28. a. Triploidy
Cells contain 69 chromosomes (karyotype
69, xxx).
Additional chromosomes encode surplus of
gene product, causing multiple anomalies
such as heart & CNS defect
1/10,000 & accounted for 15 % 0f
chromosomal abnormalities at conception.
Thus triploidyconceptions are
spontaneously aborted & those that
survived to term die shortly after birth.

29. 29
Triploidy contd.
Causes:
Dispermy fertilization of an egg
Fusion of an ovum & a polar body,
Meiotic failure: in which a diploid sperm or
egg cell is produced.

30. 30
b. Tetraploidy
92 chromosomes in each cell nucleus.
Karyotype, 92, xxxx
It is rarer than triploidy both at conception &
among live births.
It has been recorded in only a few live births
& those infants survived for only a short
period

31. 31
Tetraploidycontd.
Causes:
Mitotic failure in the early embryo in which
all of the duplicated chromosomes migrate
to one of the two daughter cells.
It can also result from the fusion of two
diploid zygotes

32. 32
2.2 Chromosome structure abnormality
chromosome numbers may be normal, but
abnormalities in chromosome structure can
cause disorders.
Chromosome breakage can lead to a variety of
rearrangements
Include: Deletions, Duplications, Inversions,
translocations

33. 33
Deletions
deficiencies or loss of a segment of a
chromosome
Terminal deletion: loss of the end of a
chromosome
Internal deletion: loss of an internal
segment of a chromosome
Effects of deletions
Large deletions are often lethal in the
heterozygous condition (dominant lethal)
Small deletions are often lethal in the
homozygous condition recessive lethal)

34. 34

35. 35
Duplications
segment of a chromosome is present in more
than one copy
Duplications usually do not have lethal effects
These mutations occur by recombination
between duplicated regions which increase
the copy number of this segment

37. 37
Inversions
a segment of a chromosome is present in
reverse order
Paracentric inversion, both breakpoints are
in the same chromosome arm & the
segment between the breakpoints is
inverted
Per centric inversion, one breakpoint
occurs in each arm & the segment between
the breakpoints is inverted

38. 38

39. 39
Translocations
Pairing of non-homologous
chromosomes in prophase I of meiosis

40. 40
Insertion

41. 41
Trisomies, non-disjunction & meternal age
Nearly all autosomal trisomies increase with
maternal age as a result of non disjunction.
Little evidence for paternal age effect on non-
disjunction

42. Trisomies, non-disjunction & meternal
age cont’d
Mothers
less than 30 -----risk is < 1/1000
At age of 35 ------risk increase to 1/400
At age of 40 ------risk increase to 1/100
At age of 45 ------risk increase to 1/25

43. 43
Summary of chromosome aberrations
Quantitative changes (duplications &
deficiencies)
Qualitative changes (inversion,
translocations, ring chromosomes)