1. And

2. A sudden change in the sequence of bases in DNA or
RNA.

3. Types of Mutations
There are a variety of types of mutations. Two major categories
of mutations are germline mutations and somatic mutations.
# Germline mutations occur in gametes. These mutations are
especially significant because they can be transmitted to
offspring and every cell in the offspring will have the mutation.
#Somatic mutations occur in other cells of the body. These
mutations may have little effect on the organism because they
are confined to just one cell and its daughter cells. Somatic
mutations cannot be passed on to offspring.
Mutations also differ in the way that the genetic material is
changed. Mutations may change the structure of a chromosome
or just change a single nucleotide.

5. Causes of Mutation
* Mutations have many possible causes. Some
mutations seem to happen spontaneously without
any outside influence.
They occur when mistakes are made during DNA
replication or transcription.
* Other mutations are caused by environmental
factors. Anything in the environment that can
cause a mutation is known as a mutagen.
Examples of mutagens are pictured
in Figure below.

7. Mutations are essential for evolution to
occur. They are the ultimate source of
all new genetic material in a species.
Most mutation are harmful, but some
mutations are beneficial.

11. (A)Numerical Abnormalities

12. 1) Aneuploidy Refers to a numerical change in part
of the chromosome set.
 Monosomic (2n-1)
-Lack of one chromosome each two identical chromosome
make bivalent, while the single chromosome not
combines with any chromosome so it’s called Univalent.
(Turner syndrome)
 Nullisomic( 2n-2)
-Lack of two chromosomes there complete absence of a pair
of identical chromosomes.
 Trisomic (2n+1)
-Increase in one chromosome, the chromosome repeats 3
times to form Trivalent. (Down syndrome)
 Tetrasomic (2n+2)
-Increase by adding 2 identical chromosomes, the
chromosome repeated 4 times to form Quatrivalent.

15. 2) Polyploidy Refers to a numerical change in the
whole chromosome set.
 Polyploidy can be induced in plants by some
chemicals as Colchicine.
 Autopoly ploidy:
Are polyploids with multiple chromosomes sets derived
from single species as (Potato & Banana).
 Allopolyploidy:
Are polyploids with chromosomes derived from
different species as Triticale (6 sets); 4 from
wheat(Triticum turgidum) & 2 from rye(Secale
cereale).

16. Examples
 Triploid(3 sets) Seedless
watermelon/Salamanders.
 Tetraploid(4 sets) Durum “ macaroni wheat”
 Hexaploid(6 sets) Bread wheat.
 Dodecaploid(12 sets) Xenopus genus.
 In humans it rarely occur in liver cells, heart
muscle & in bone marrow.

17. (B) Structural Abnormalities
 Structural abnormalities are mutations that change
chromosome structure.
 They occur when a section of a chromosome breaks
off and rejoins incorrectly or does not rejoin at all.
 Possible ways these mutations can occur are illustrated
in Figure below.

18. Chromosomal alterations are major
changes in the genetic material.

19.  A point mutation is a change in a single nucleotide in
DNA. This type of mutation is usually less serious than
a chromosomal alteration.
 Point mutations can be silent, missense, or
nonsense mutations, as shown in Table below.
 The effects of point mutations depend on how they
change the genetic code.

20.  Type Descriptio
n
 Example  Effect
Silent  Mutated
codon codes
for the same
amino acid
 CAA
(glutamine) →
CAG (glutamine)
 None
Missense  Mutated
codon codes
for a different
amino acid
 GAG (glutamic
acid) → GTG
(valine)
 Variable
Nonsense
 Mutated
codon is a
premature
stop codon
 CAA
(glutamine) →
UAA (stop)
usually
 Serious

23. A frameshift mutation is a
deletion or insertion of one
or more nucleotides that
changes the reading frame
of the base sequence.
Deletions remove
nucleotides, and insertions
add nucleotides.

24.  DNA repair systems are vital to the survival of all
organisms.
– Living cells contain several DNA repair systems
that can fix different types of DNA alterations.
 In most cases, DNA repair is a multi-step process:
1. An abnormality in DNA structure is detected.
2. The abnormal DNA is removed.
3. Normal DNA is synthesized.

25. 1) Direct Repair System

26. 2-Base excision repair(BER)
system
 Base excision repair (BER) involves a category of
enzymes known as DNA-N-glycosylases :
– These enzymes can recognize a single damaged base and
cleave
the bond between it and the sugar in the DNA.
– Removes one base, excises several around it, and
replaces with
several new bases using Pol adding to 3’ ends then ligase
attaching
to 5’ end.
 Depending on the species,, this repair system can
eliminate abnormal bases such as:
– Uracil; Thymine dimers

28. 3-Nucleotide excision
repair(NER) system
 This type of system can repair many types of DNA damage,
including:
– Thymine dimmers and chemically modified bases
 NER is found in all eukaryotes and prokaryotes
– However, its molecular mechanism is better understood in
prokaryotes.
 Several human diseases have been shown to involve
inherited defects in genes involved in NER:
– These include xeroderma pigmentosum (XP) and Cockayne
syndrome (CS)
" A common characteristic of both syndromes is an increased
sensitivity to sunlight “

30. Proofreading
enzymes
Correct errors
made during
replication

31. 4-Mismatch repair(MMR)system
 If proofreading fails, the methyl-directed mismatch
repair system comes to rescue.
 This repair system is found in all species.
 In E.coli by using (MutH,MutS & MutL) .
 Methyl-directed mismatch repair recognizes
mismatched base pairs, excises the incorrect bases,
and then carries out
repair synthesis.
 Eukaryotes also have mismatch repair, but the
mechanism to distinguish the template strand from the
new strand is still unclear.
– Four genes are involved in humans, hMSH2 and
hMLH1, hPMS1, and hPMS2.

34. Thank
You