The document discusses the genetic material in cells. It describes chromosomes as structures that contain DNA and proteins where genes are located. DNA is a double-helix molecule that contains the genetic instructions for cells. DNA replication ensures each cell receives the same genetic information by duplicating the DNA. Chromosomes determine traits and there are usually 23 pairs in human cells. Abnormalities like Down syndrome occur when an extra chromosome is present. The discovery of DNA's structure showed it directs cellular activities and traits through genes on its double helix. DNA replicates through enzymes unwinding and separating its strands, then new complementary strands are built.

1. The
Genetic
Material

2. SUBTOPICS:
CHROMOSOME
DNA STRUCTURE
DNA REPLICATION

3. Chromosome
Rod- shaped structure that forms when a
single DNA molecule and its associated
proteins coil tightly before cell division.
It is where genes are located.
GENES
segment
of
DNA
that
transmits
information from parent to offspring
DEOXYRIBONUCLEIC ACID (DNA)
a long, thin molecule that contains the
information needed to direct cell’s
activities
and
to
determine
cell’s
characteristics.

4. Structure of Chromosome:
CHROMATID
- one of a pair of strands of DNA that
make up a chromosome during
meiosis and mitosis
- forms prior to cell division when the
DNA molecule duplicates itself,
ensuring that each new cell will have
the same genetic information as the
old cell
CENTROMERE
- region joining the two chromatids

6. Human cells have 23 different
chromosomes. Your body cells (also called
SOMATIC CELLS) contain 2 copies of each
chromosome, for a total of 46
chromosomes.
HOMOLOGOUS CHROMOSOMES
- similar in shape, size and the genes
they carry
DIPLOID
- cell containing 2 homologues of each
chromosome (2n)

7. GAMETES – egg cells and sperm cells
HAPLOID
– cell contains only 1 homologue
of each chromosome
- the fusion of 2 haploid gametes
form a diploid zygote
ZYGOTE
- a fertilized egg cell, the first cell
of a new individual

8. Being haploid ensures that when an egg and
sperm fuse,
the resulting zygote will contain
characteristic
diploid
number
chromosome for that organism.
the
of

9. CHROMOSOMES AFFECT
DEVELOPMENT:
 Each of the 46 human chromosomes has
thousands of genes that play important
roles in determining how a person body
develops and functions.
MONOSOMY – condition in which a diploid
cell is missing a chromosome
TRISOMY – condition in which a diploid cell
has an extra chromosome

10. KARYOTYPE
– collection of chromosomes
found in an individual’s cells which
are arranged in order of size and
shape

11. TRISOMY 21 or DOWN’S SYNDROME
- described in 1866 by J. Langdon Down
- features: short stature, round face with
upper eyelids that cover the inner
corners of the eyes and varying degrees
of mental retardation
- It is much more common in children of
older mothers

12. Why more babies with Down Syndrome are
born to older mothers?
The reason that more babies with Down
Syndrome are born to older mothers is that all
the eggs a female will ever produce are
present in her ovaries when she is born. As the
female ages, the eggs can accumulate an
increasing amount of damage.
What events cause an individual to have an
extra copy of chromosome?
When a cell divides normally, each
chromosome and its homologue separate, an
event called DISJUNCTION.

13.  When normal disjunction does not occur, 1
or more chromosome may fail to separate
properly, causing an accident in chromosome
separation called NONDISJUNCTION.
- results in 1 new cell receiving both
chromosome and the other new cell
receiving none

14. ALTERATIONS IN CHROMOSOME STRUCTURE:
MUTATIONS
– changes in an organism’s genetic
material
Forms of Mutation:
DELETION – mutation in which a nucleotide or
segment of DNA is lost

15. DUPLICATION – mutation in which
chromosome contains an extra
copy of a segment of DNA

16. INVERSION – mutation in which a
chromosome fragment rejoins
its original chromosome with
its nucleotides reversed

17. TRANSLOCATION – mutation caused by a
chromosome fragment joining
a nonhomologous chromosome
during cell division

18. CHROMOSOME DETERMINE YOUR SEX:
Of the 23 pairs of chromosomes in human
somatic cells, 22 pairs are the same in males
and females.
o AUTOSOMES – a chromosome that is not
directly involved in determining sex
o SEX CHROMOSOMES – chromosomes that
differ between males and females
that carry the genes that determine
an individual sex
- exist in either 2 forms:
X and shorter Y chromosome

19. In humans and many other organisms, the
genes that cause a fertilized egg to develop
into a MALE are located on the Y
chromosome. Thus, any individual with a Y
chromosome is a MALE and any individual
with an X chromosome is a FEMALE.
FEMALES are designated XX because they
have two X chromosomes.
MALES are designated XY because they have
one X chromosome and one Y chromosome.
Because a female can donate only an X
chromosome to her offspring, the sex of an
offspring is determine by the male who can
donate either an X or Y.

20. In some insects, such as grasshoppers,
there is no Y chromosome. In such cases, the
females are characterized as XY and the
males as XO (O indicates the absence of
chromosome).
In birds, moths and butterflies, the male has
two X chromosomes and the female only one.

21. DISCOVERY OF THE DNA:
 1928 – Frederick Griffith demonstrates
TRANSFORMATION
- transfer of genetic material from
one organism to another
- prepared a vaccine against the
pneumonia- causing bacterium
STREPTOCOCCUS PNEUMONIAE
• VACCINE – substance prepared from
killed or weakened
microorganism that is introduced
into the body to produce
immunity

22. • VIRULENT – refers to the deadliness of a
disease- causing agent
 1944 – Oswald Avery and his colleagues
demonstrated that DNA was
responsible for the transformation
- made the announcement that genetic
material was DNA
 1952 – Alfred Hershey and Martha Chase
showed that genes are made of DNA
- used a type of bacteriophage (T2
phage) -> virus that infects bacteria

23. DNA Structure:
DNA is an extraordinarily long, thin
molecule made of subunits called nucleotides
that are linked together like a chain.
 NUCLEOTIDES – building blocks of DNA
3 parts:
• Phosphate group
• Five- carbon sugar molecule
• Nitrogen base
While the sugar molecule and the
phosphate group are the same for each
nucleotide in a molecule of DNA, the
nitrogen base may be any one of four
different kinds.

24. 4 kinds of nitrogen base:
• Adenine and Guanine – belong to a class of
organic molecule which is,
PURINES – large molecules with a double
ring of carbon and nitrogen atoms
• Thymine and Cytosine – belong to a class of
organic molecule which is,
PYRIMIDINES – have a single ring of
carbon and nitrogen atoms

25.  1949 – Erwin Chargaff made an interesting
observation about DNA. Chargaff’s
research data showed that for the DNA in
each organism, the amount of adenine
always equals the amount of thymine.
Likewise, the amount of guanine always
equals the amount of cytosine.
- the findings known as Chargaff’s rules
or more commonly as the BASE-PAIRING
RULES, suggested that the precise
arrangement of nucleotides within a DNA
molecule specifies genes

26. 1952 – Maurice Wilkins and Rosalind Franklin,
developed some high- quality X- ray
diffraction photographs of the DNA
molecule
- it suggested that DNA molecule
resembled a tightly coiled helix and was
composed of 2 or 3 chains of nucleotides

27.  1953 – James Watson and Francis Crick, used
a tin-and-wire models of molecules, they
built as a model of DNA with the
configuration of DOUBLE- HELIX, “a spiral
staircase” of 2 strands of nucleotides
twisting around a central axis.
The sides of ladder are constructed
of alternating sugar and phosphate units,
and each rung is a purine and a pyrimidine
held together by hydrogen bonds.

28. Why is purine always paired with a
pyrimidine?
These base pairing are the only possible
arrangement because (A) can form hydrogen
bonds only with (T) and (C) can form
hydrogen bonds only with (G).
The strictness of base pairing results in 2
strands that are COMPLEMENTARY to each
other; that is the sequence of bases on 1
strand determines the sequence of bases on
the other strand.

29. For example, if the sequence of 1 strand of DNA
molecule is TCGAACT, the sequence on the other
strand:
AGCTTGA
HOW IS DNA COPIED:
 REPLICATION – process of synthesizing a new
strand of DNA

30. 
HELICASES – enzymes that unwind a DNA
molecule’s double helix before replication
- open up the double helix by
breaking
the hydrogen bonds that link the
complementary bases
- once the 2 strands are separated,
additional enzymes and proteins attach to
the individual strands and hold them
apart, preventing them from twisting

31.  REPLICATION FORK – point at which the
double helix separates (Y Shape)
 DNA POLYMERASES – enzymes that catalyze
the replication of DNA
- add nucleotides to the exposed
bases
- As it move along, new double helix
are formed.
- Once it has began adding
nucleotides to a growing double helix, the
enzyme remains attached to the strand
until it reaches a signal that tells it to
detach.

32. An important feature of DNA replication is that
DNA polymerase has a “PROOFREADING ROLE”
- it can add nucleotides to a growing strand
only if the previous nucleotide is correctly paired
to its complementary base.
In an event of a mismatched nucleotide,
DNA polymerase is capable of backtracking,
removing the incorrect nucleotide and replacing
it with the correct one.
This proofreading prevents error in DNA
replication.

33. Thank you!
God bless everyone 
Presenter:
Zendle Ann Loria Olarte