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1. and
Organization
Genome
Structure

2. Difference between prokaryotes
and eukaryotes
In eukaryotes:
1. The nuclear genome is split into a
number of individual DNA molecules
2. The DNA molecules are linear
3. there are two copies of each
chromosome in most cells
Human chromosomes

3. In eukaryotes:
4. The integrity of individual genes can be interrupted .
5.There may be multiple and identical copies of particular sequences .
6.There may be large blocks of DNA that do not code for protein.
7.The arrangements for gene expression in eukaryotes must bedifferent
from those in prokaryotes .

4. C-value
• Means Constant or Characteristic
value
• is the amount of DNA in the haploid
genome of an organism
• Measured in picogram

5. False idea:
complexity of an organism
is directly proportional
with its genome size
There is no direct
correlation between:
➢ Genome size and
organism’s complexity
➢ Genome size and
chromosome number

6. • Ex: The toad Xenopus and man
have genomes of essentially the
same size , but we assume that
man is more complex in terms of
genetic development
1-genome size not related
to genetic complexity

7. 2-There is no correlation between
genome size and chromosome number
Saccharomyces cerevisiae
• Genome = 12.1 MB
• Split into 16 chromosome
Human
• Has DNA more about 150 times
(3200MB)
• Haploid complement of only 23
chromosomes

8. kinetics of the reassociation or reannealing reaction
• in molecular biology and genetics refers to the process of two
complementary single-stranded DNA molecules coming together and
forming a double-stranded DNA molecule.
• biochemical studies on purified eukaryotic DNA
purified nucleic eukaryotic DNA
Heat
The 2 strands separate
Allow to cool
DNA started coming together much faster than
was expected onthe basis of separated strands of
single genes finding each other.
Observation

9. “Fast reassociating DNA is low complexity”
• Repetitive DNA: a class of DNA that was present in many copies in the
genome
• Repetitive frequency (f): The number of copies present per genome
So, Do large genomes contain a greater number of different
genes or instead more copies of the same genes?
• a substantial part of the eukaryotic genome is made of repetitive DNA
or individual sequence elements that are repeated many times over ,
either in tandem arrays or interspersed throughout the genome.
conclusion

10. “There is an increase in the minimum genome size found in
each group as the complexity increases”
• Minimum Genome Size: It represents the minimal set of
genes necessary for the basic biological processes of
that organism.
• Groups: (e.g., different species, genera, families, or
orders) or other criteria like ecological roles or lifestyles.
• Complexity: More complex organisms typically have
more specialized cell types, tissues, organs, and
behaviors. They often perform a wider range of
functions and have more sophisticated life strategies.
• Increase in Minimum Genome Size: more complex
organisms generally require a larger set of genes to
support their complex functions and traits.
Therefore, It is necessary to increase the genome size in order to make insects ,
birds , amphibians and mammals.

11. Eukaryotic DNA
Non repetitive or
single copy DNA
sequences or
functional genes
Repetitive DNA
functional
sequence
Noncoding
functional
sequence
Telomeres
Families of coding
(and related
pseudogenes)
Dispersed gene
families
Tandem gene
families
“tandem array”
sequence with no
known function
Repeats in
centromeric
heterochromatin
“satellite”
Variable Number
Tandem Repeats
“VNTRs”
Transposonses
sequence
Transposons Retro transposons
Spacer DNA

13. (1) Non repetitive or single copy DNA
sequences.
• Present in single or low copy numbers.
• Includes coding sequence for structural genes (up to 1400 bp
in size),which account for 3% of the genome.
• The remainder is intrinsic sequence or spacer DNA
• portion of the genome that does not consist of repetitive
elements or sequences
• R= 1 or 2
• contains the genetic information necessary for encoding
proteins and regulating gene expression.
• plays a central role in determining an individual's traits,
functions, and overall biology

14. The organism The presence of non repetitive sequences
Prokaryotes only non repetitive DNA
Lower eukaryotes most of the DNA is non repetitive , < 20% falls into one or more moderately repetitive
components.
plants and amphibians the non repetitive DNA may be reduced to a minority of the genome , with the
moderately and highly repetitive components accounting for up to 80%
animal cells up to half of the DNA often is occupied by moderately and highly repetitive
components.
(1) Non repetitive or single copy DNA
sequences.

15. Eukaryotic DNA sequence

16. complexity is a multifaceted concept influenced
by various genetic and non-genetic factors.
• There is an increase in the minimum genome size found in each group
as the complexity increases
• It is necessary to increase the genome size in order to make insects ,
birds , amphibians and mammals.

17. (2) Repetitive DNA sequences.
• Functional coding sequence
a. Families of coding genes :
➢Dispersed gene families
❑Gene families are the representation of all those genes which are
originated from 1 ancestor gene due to duplication
❑Those genes are scattered rather than clustered and this scattered
distribution occurs due to gene duplication followed by gene
movement or transpostioins
❑several types of proteins are encoded by families of homologous
genes spread throughout the genome

18. families may comprise only a
few genes or very many
Gene family Number of genes
Actin from 5 to 30 genes
Keratin > 20 genes
Tubulins 3-15 genes
Histones 100-1000 genes
(2) Repetitive DNA sequences.

19. ➢Tandem gene family arrays:
▪ Tandem copies of rRNA genes in the
nucleolar organizer are essential for the
efficient production of ribosomal RNA,
which, in turn, supports the cell's ability to
synthesize proteins. Since ribosomes are
fundamental to protein synthesis, the
nucleolar organizer plays a crucial role in
cellular processes related to growth and
protein production.
(2) Repetitive DNA sequences.

20. ➢Tandem gene family arrays:
▪ One human Nucleolar Organizer (NO) has
about 250 copies of rRNA genes .
▪ For ensuring a large amount of rRNA per cell
because Cells need large amount of the
products of some genes
(2) Repetitive DNA sequences.
NOR

21. b. Non-coding functional sequences:
➢Telomeres:
▪ They are specialized structures located at the ends of linear
chromosomes in eukaryotic cells.
▪ consist of repetitive DNA sequences that are repeated hundreds to
thousands of times.
▪ Human telomeric sequence is 5’-TTAGGG-3’
▪ solve a functional problem that is inherent in the replication of the
ends of linear DNA molecules (end replication problem).
(2) Repetitive DNA sequences.

22. • Non-Functional repetitive
sequence
• 20% of the human genome
consists of nonfunctional
repetitive sequences of one kind
or another
a. Highly repetitive centromeric
DNA
(2) Repetitive DNA sequences.

23. • b. VNTRs:
• A special class of tandem repeats which shows variable number at different
chromosomal positions and in different individual members of a species.
• This type of repeat is called " Variable Number Tandem Repeat "
( VNTR), and sometimes called " Minisatellite DNA“.
• The VNTR loci in humans are 1-5 kb sequences.
• Consisting of variable numbers of repeating unit from 15 to 100
nucleotides long.
• These minisatellite DNA are very useful as "DNA fingerprints " . They are
used extensively in forensic medicine.
(2) Repetitive DNA sequences.

24. • b. VNTRs:
• Another class of dispersed repetitive DNA is composed of few
nucleotides (1-6) .
• This class of repetitive DNA is called " Microsatellite DNA " .
• Microsatellites are in fact dispersed regions composed of variable
numbers of few nucleotides repeated in tandem .
• Because the numbers of repeats varies between individuals, this type
of DNA has been most useful in providing a dense array of molecular
mark for genome mapping .
(2) Repetitive DNA sequences.

25. • c. Transposed sequences
• A large proportion of a eukaryotic genome is composed of repetitive
elements that have propagated within the genome by making copies
of themselves , which can move into new locations .
• These element collectively called transposed sequences
(2) Repetitive DNA sequences.

26. (3) Spacer
• The final (class/category) of DNA is spacer DNA , which is basically
what is the left after all the recognizable units have been identified.
• Possibly its function is to space , but no studies have yet been
performed to delete such DNA and observe the consequence.
• The amount of repetitive DNA is probably the main factor that
determines the size of an organism's genome Packaging /
Organization of DNA into Chromosome