Chromosomal aberrations

1. CHROMOSOME
Presented by:
1. Shadia Rahman
ID - 2015-1-77-009
2. Muhammad Jahid Mostofa
ID - 2015-1-77-033
3. Sania Naz
ID - 2015-1-77-050
4. Jannaty eva
ID - 2015-2-77-003
5. Asma Hossain
ID - 2015-2-77-004

2. What is Chromosome
Chromosome is a threadlike structure of nucleic acids and
protein found in the nucleus of most living cells, carrying
genetic information in the form of genes.
The term chromosome comes from the Greek words for color
(chroma) and body (soma). Scientists gave this name to
chromosomes because they are cell structures, or bodies,
that are strongly stained by some colorful dyes used in
research.
Where is the location of genes in Chromosome?
The total complement of genes in an organism or cell is
known as its genome, which may be stored on one or
more chromosomes. The region of the chromosome at
which a particular gene is located is called its locus.

3. Number of Chromosomes in humans
 Autosomes (body chromosomes):
An autosome is a pair of chromosomes in a diploid
cell in which each chromosome has the same form.
 Allosome (sex chromosomes):
An allosome is a chromosome that differs from an
ordinary autosome in form, size, and behavior.
 For example, humans have a diploid genome that
usually contains 22 pairs of autosomes and one
allosome pair (46 chromosomes total).

4. Chromosome Structure
Telomere: Telomeres are repetitive stretches of DNA located at the ends of
linear chromosomes. They protect the ends of chromosomes in a manner similar
to the way the tips of shoelaces keep them from unraveling.
In many types of cells, telomeres lose a bit of their DNA every time a cell divides.
Eventually, when all of the telomere DNA is gone, the cell cannot replicate and
dies.
White blood cells and other cell types with the capacity to divide very frequently
have a special enzyme that prevents their chromosomes from losing their
telomeres. Because they retain their telomeres, such cells generally live longer
than other cells.
Telomeres also play a role in cancer. The chromosomes of malignant cells usually
do not lose their telomeres, helping to fuel the uncontrolled growth that makes
cancer so devastating.
Centromere: The constricted region of linear chromosomes is known as the
centromere. Although this constriction is called the centromere, it usually is not
located exactly in the center of the chromosome and, in some cases, is located
almost at the chromosome's end. The regions on either side of the centromere are
referred to as the chromosome's arms.
Centromeres help to keep chromosomes properly aligned during the complex
process of cell division. As chromosomes are copied in preparation for production
of a new cell, the centromere serves as an attachment site for the two halves of
each replicated chromosome, known as sister chromatids.

5. Chromosome Structure
 Kinetochore: A complex of
proteins associated with the
centromere of a chromosome
during cell division, to which the
microtubules of the spindle
attach.
 The origin of
replication (also called
the replication origin):
It is a particular sequence in a
genome at which replication is
initiated. This can either involve
the replication of DNA in living
organisms such as prokaryotes
and eukaryotes, or that of DNA
or RNA in viruses, such as
double-stranded RNA viruses.

6. Four Major Types of Chromosome
Based on position of centromere
 METACENTRIC CHROMOSOMES:
Metacentric chromosomes have the centromere in the center, such that both
sections are of equal length. Human chromosome 1 and 3 are metacentric.
 SUBMETACENTRIC CHROMOSOMES:
Submetacentric chromosomes have the centromere slightly offset from the
center leading to a slight asymmetry in the length of the two sections. Human
chromosomes 4 through 12 are submetacentric.
 ACROCENTRIC CHROMOSOMES:
Acrocentric chromosomes have a centromere which is severely offset from
the center leading to one very long and one very short section. Human
chromosomes 13,15, 21, and 22 are acrocentric.
 TELOCENTRIC CHROMOSOMES:
Telocentric chromosomes have the centromere at the very end of the
chromosome. Humans do not possess telocentric chromosomes but they are
found in other species such as mice.

8. Functions of Chromosomes
 Genetic Code Storage: Chromosome contains the genetic material
that is required by the organism to develop and grow. DNA molecules
are made of chain of units called genes. Genes are those sections of the
DNA which code for specific proteins required by the cell for its proper
functioning.
 Sex Determination: Humans have 23 pairs of chromosomes out of
which one pair is the sex chromosome. Females have two X
chromosomes and males have one X and one Y chromosome. The sex
of the child is determined by the chromosome passed down by the male.
If X chromosome is passed out of XY chromosome, the child will be a
female and if a Y chromosome is passed, a male child develops.
 Control of Cell Division: Chromosomes check successful division of
cells during the process of mitosis. The chromosomes of the parent cells
insure that the correct information is passed on to the daughter cells
required by the cell to grow and develop correctly.
 Formation of Proteins and Storage: Proteins are essential for the
activity of a cell. The chromosomes direct the sequences of proteins
formed in our body and also maintain the order of DNA. The proteins are
also stored in the coiled structure of the chromosomes. These proteins
bound to the DNA help in proper packaging of the DNA.

9. Prokaryotic versus Eukaryotic
Chromosomes

11. DNA Packaging into Chromosomes
 The cell likes to keep things tidy, ordered, and
longshoreman-free. It packs DNA so that it does not take
up too much space. If you were to stretch out all of the
DNA in your body end-to-end, it would be approximately
1.2 × 1010 miles, which is about 70 trips to the Sun and
back.
 The double helix of DNA is highly negatively charged due
to all the negatively charged phosphates in the backbone.
All that negative charge must be counterbalanced by a
positive charge, and the cell makes proteins
called histones that bind DNA and aid in DNA's packaging.
Histones are positively charged proteins that wrap up DNA
through interactions between their positive charges and the
negative charges of DNA. Double-stranded DNA loops
around 8 histones twice, forming the nucleosome, which is
the building block of chromatin packaging.

14. Histones are divided into two groups:
#Core histones
#Linker histones
Core histones are H2A, H2B, H3, and H4, where two
H3/H4 dimers (H3 and H4 hooked together) and two H2A/H2B
dimers (these two hooked together) form the octamer (all eight of
these guys together). Linker histone H1 basically locks the DNA in
place onto the nucleosome and can be removed for transcription.

15. Chromosome Aberration
 Chromosome aberration: An irregularity in the
number or structure of chromosomes, usually a
gain, loss, exchange, alteration of sequence of
genetic material, which often alters embryonic
development.
 Chromosome abnormalities typically occur as a result of errors
in one, or more, of the following: meiosis, mitosis, maternal age,
or environment. They underlie genetic disease in roughly 15%
of patients with multiple congenital abnormalities and/or mental
retardation (MCA/MR).
 Two types chromosome aberration:
 Structural chromosome aberration
 Numerical chromosome aberration

18. ANY QUESTIONS??
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