A mutation is a permanent alteration in the DNA sequence of a gene that differs from what is typically found. Mutations can range in size from a single DNA building block to a large chromosome segment including multiple genes. There are several types of chromosomal mutations, including deletions, duplications, inversions, translocations, and disjunctions. An inversion occurs when a chromosome segment is cut out, flipped, and reinserted. Inversions are either paracentric or pericentric depending on if the centromere is inside or outside the inverted region. During meiosis, inversions can lead to deletions or gene imbalances if crossovers occur within the inverted region, resulting in non-viable gametes or z

1. MUTATION
Presented by:
Tousif Khan
Subham Karmakar
Suravi Saha Roy
Pranab Karmakar
Rahul Naskar
Vijaygarh Jyotish Ray College
Zoology dept.
Created by Tousif Khan

2. Mutation
A mutation is a permanent alteration in the DNA sequence that
makes up a gene, such that the sequence differs from what is found in
most people. Mutations range in size; they can affect anywhere from a
single DNA building block (base pair) to a large segment of a
chromosome that includes multiple genes.
Types of Chromosomal Mutation
Deletion
Duplication
Inversion
Translocation
Disjunction

3. Inversion
A segment of a chromosome is cut out, flipped, and reinserted.
Inversions are of two basic types :
Paracentric - If the centromere is outside the inversion, the inversion is
said to be paracentric.
Pericentric - If the centromere is inside the inversion, the inversion is
said to be paracentric.
Centromere

4. Individuals with inversions
are generally normal, if
there are no breaks
within genes. A break
that disrupts a gene
produces a mutation
that may be detectable
as an abnormal
phenotype. If the gene
has an essential function,
then the break point acts
as a lethal mutation
linked to the inversion.

5. Inversion heterozygote
Most analyses of inversions are carried out on diploid cells that contain
one normal chromosome set plus one set carrying the inversion. This type
of cell is called an inversion heterozygote.
Inversion loop
In meiosis, one chromosome twists once at the ends of the inversion to
pair with its untwisted homolog; in this way, the paired homologs form a
visible inversion loop.

6. In a paracentric inversion, crossing over
within the inversion loop at meiosis
connects homologous centromeres in a
dicentric bridge while also producing an
acentric fragment. Then, as the
chromosomes separate in anaphase I, the
centromeres remain linked by the bridge.
The acentric fragment cannot align itself or
move; consequently, it is lost. Tension
eventually breaks the dicentric bridge,
forming two chromosomes with terminal
deletions. Either the gametes containing
such chromosomes or the zygotes that they
eventually form will probably be in viable.
Hence, a crossover event, which normally
generates the recombinant class of meiotic
products, is instead lethal to those
products.
Inversion to Deletion (Paracentric)

7. In a heterozygous Pericentric inversion,
the net genetic effect is the same as
that of a paracentric inversion—
crossover products are not recovered—
but the reasons are different. In a
Pericentric inversion, the centromeres
are contained within the inverted
region. Consequently, the
chromosomes that have engaged in
crossing over separate in the normal
fashion, without the creation of a
bridge. However, the crossover
produces chromatids that contain a
duplication and a deletion for different
parts of the chromosome. In this case, if
a gamete carrying a crossover
chromosome is fertilized, the zygote
dies because of gene imbalance.
Inversion to Deletion (Pericentric)