1. DR IFAT ARA BEGUM
Assistant Professor (Biochemistry)
Dhaka Medical College, Dhaka
2.
3. DNA contains original codes for making
protein that living cells need.
mRNA is a copy of a gene located on the
DNA molecule.
mRNA will leave the nucleus of the cell
and the ribosome will read its coding
sequences and put the appropriate
amino acids together.
4.
5.
6. Unit of heredity/inheritance/ genetic information,
arranged along the chromosome in linear order
Gene is the functional unit of DNA , composed of
coding region with its regulatory sequences that
carry genetic information encoded within the base
sequence of coding region.
Majority of genes are on chromosome in nucleus.
( only 37 genes on naked loop of mitochondrial
DNA).
7. Coding region : A mosaic of exons (E) and
introns (I)
Exons: Discrete units of DNA within the coding
segment that contain genetic code and are
expressed. They are found in the mature transcript
(messenger RNA).
Introns: Non-coding units of DNA interposed
between exons within the coding segment. They
are transcribed but not included in mature mRNA
and are not expressed. The introns are removed
from the primary transcript by a process called
splicing
8. The coding region begins with the
initiation codon, which is normally ATG.
It ends with one of three termination
codons.
On either side of the coding region are
DNA sequences that are transcribed but
are not translated. These untranslated
regions or non-coding regions often
contain regulatory elements that control
protein synthesis
9. Regulatory sequences: Coding region is flanked
by these sequences, also called transcription control
sequences.
i. Promoter sequences: Consists of TATA box,
GC box & CAAT box, lies towards the 5’ end
(upstream) of gene and initiates transcription.
ii. Terminator sequences: Lies towards 3’ end
(downstream) of gene and terminates transcription.
10. iii. Enhancer: lies in upstream/ downstream/ within
coding region and accelerates transcription.
iv. Silencer: lies in upstream/ downstream/ within
coding region and suppresses transcription.
Regulatory sequence is flanked by leader
sequence (5’ UTR) in 5’ end & trailer sequence (3’
UTR) in 3’ end.
UTR--- Untranslated region
11.
12.
13. There are two general types of gene
in the human genome:
1. Non-coding RNA genes
and
2. Protein-coding genes
14. Non-coding RNA gene:
o Represents 2-5 per cent of the total and
encode functional RNA molecules.
o Many of these RNAs are involved in the
control of gene expression, particularly
protein synthesis.
o They have no overall conserved structure.
15. Protein-coding gene:
o Represent the majority of the total and are
expressed in two stages: transcription and
translation.
o They show incredible diversity in size and
organization and have no typical structure.
o There are, however, several conserved
features.
16. The smallest protein-coding gene in the human
genome is only 500 nucleotides long and has no
introns. It encodes a histone protein.
The largest human gene encodes the protein
dystrophin, which is missing or non-functional in
the disease muscular dystrophy. This gene is 2.5
million nucleotides in length and it takes over 16
hours to produce a single transcript.
However, more than 99 per cent of the gene
made up of its 79 introns.
17. Position occupied by a specific gene on a
specific chromosome.
It is mentioned with reference to centromere
( connection point between 2 sister
chromatids as chromosome splits
longitudinally).
Genes don’t change the loci except in
recombination during cross over ( at meiosis)
or in alteration of chromosomal morphology.
18.
19.
20. Total genetic message encoded in the base
sequence of exons of coding region of gene.
OR
The genetic code is the set of rules by which
information encoded within genetic material
(DNA or mRNA sequences) is translated into
proteins by living cells. This information in DNA is
in the form of triplet codons. Each codon specifies
one amino acid in the protein.
SO
Anatomically, Genetic code is the collection of
codons that specify amino acids .
21.
22.
23. Every individual three letter code word of
genetic code .
Anatomically, it is triplet (3) consecutive
bases, composed of A, T, G & C at
different combinations.
Each codon represents one amino acids
24.
25. Total 64 codons which is of 2 types:
a) Sense codon: Represents one amino acid to
carry on protein synthesis. There are 61 sense
codons.
b) Nonsense codon: Also called stop codon.
They are 3 in number, don’t sense any amino
acid and are used to terminate protein
synthesis. These are: UAA, UAG, UGA.
26.
27. 1. Universality: A codon representing a
definite amino acid, specifies same amino
acid in all species.
2. Redundancy/ Degeneracy: For a given
amino acid, there is more than one codon
(except methionine & tryptophan).
Here 1st 2 bases are same mostly (5’->3’),
alteration is seen in 3rd base. e.g. Valine
(GUU, GUC, GUA & GUG)
29. 4. Nonoverlapping: Consecutive triplet
codons don’t share any base and follow
the strict sequence along the reading
frame of mRNA.
30.
31. 5. Commaless/ Nonpunctuated: Between
consecutive codons, there is no extra base to
separate the codons.
The last nucleotide of preceding codon is
immediately followed by the first nucleotide
of succeeding codon.
The genetic code is read from a fixed point
in a continuous sequence of triplet codons
without any punctuation between the codons.
32.
33.
34. Total genetic make up of a cell.
or
According to modern molecular biology
and genetics, the total genetic material of
an organism that is encoded in DNA (for
many types of viruses in RNA).
The genome includes both the genes and
the non-coding sequences of the
DNA/RNA.
35.
36.
37.
38. EvEry living organism
IS
The Outward Physical
Manifestation
Of
Internally Coded Inheritable
Information
39. This is the outward, physical
manifestation/appearance of an
organism/an individual for any particular
character/trait.
It is the observed expression of a gene
produced as an outcome of the interaction
between genotype and environmental
factors.
40.
41.
42. Phenotype is potentially variable, as it is
the product of interaction between genotype
and environmental factors.
Environmental factors include intrauterine
feeding, postnatal feeding and hormonal
exposure, exercise, sunlight etc.
AS internal environmental factors like
endocrine and nutritional disorders can
suppress the action of genotype, an
individual with tall genotype for height (TT)
may be short. .
43. Internally coded, inheritable information
(genetic information) carried by all living
organisms that defines the phenotype of them.
This stored information is used as a
"blueprint" or set of instructions for building
and maintaining a living creature.
These instructions are found within almost all
cells (the "internal" part), they are written in a
coded language (the genetic code).
44. They are copied at the time of cell division
or reproduction and are passed from one
generation to the next ("inheritable").
These instructions are intimately involved
with all aspects of the life of a cell or an
organism. They control everything from the
formation of protein macromolecules, to the
regulation of metabolism and synthesis.
45. Genotype is fixed at the time of
fertilization and does not vary later on.
Genotype of tall individual is TT or Tt
T: Dominant gene for tall
t: Recessive gene for short
46.
47.
48. Easy to remember:
Phenotype is observable characteristic
of an organism/individual
Genotype is genetic composition of
allele
49.
50.
51. A genetically determined physical
characteristic.
It may be: single gene trait (trait
determined by a single gene pair)
Or
polygenic trait (trait
determined
by many genes)
Most of the hereditary traits are polygenic
which are produced by interaction of many
genes & conditioned by environment.
52. A trait is some aspect of an organism that
can be described or measured.
The phenotype is the observed state of the
trait.
A trait is eye color, a phenotype is having
blue eyes.
53. Homologous copies of a gene.
OR
Alternative form/forms of a gene occupying the
homologous loci of homologous chromosome
(controlling same characteristic but may
produce different effect)
Homologous Chromosome: Chromosomes identical
to each other with respect to length, physical look,
centromere position, banding pattern & gene
distribution.
Homologous gene: Identical gene occupying the
homologous loci of homologous chromosome
54.
55. There may be multiple alleles of a gene but
one chromosome bears only a single allele at
a given locus.
If two allelic genes occupying homologous
loci are same , it is called homozygous, and
if not same, it is called heterozygous.
In homozygous situation, homologous pair of
chromosome carry same genes.
In heterozygous situation, homologous pair
of chromosome carry different genes.
56.
57. If paired allele is TT or tt, it is homozygous
and will express as tall and short
respectively
BUT
If paired allele is Tt, it is heterozygous and
will express as tall, since ”T” is dominant
allele for tall over “t”, the recessive allele for
short.
58.
59. An organized profile of a person's
chromosomes.
OR
A complete set of metaphase chromosome of
an individual/cell.
Two chromosomes specify gender — XX for
female and XY for male. The rest are
arranged in pairs, numbered 1 through 22,
from largest to smallest. This arrangement
helps scientists quickly identify chromosomal
alterations that may result in a genetic
disorder.
60.
61. Individual Karyotype
Normal male 46 XY
Normal female 46 XX
Down Syndrome (male) 47 XY + 21 (Trisomy 21)
Down Syndrome (female) 47 XX + 21 (Trisomy 21)
Turner Syndrome 45 X
62. To make a karyotype, scientists take a
picture of the chromosome from one cell,
cut them out, and arrange them using
size, banding pattern, and centromere
position as guides.
63. The procedure to make out karyotype of an
individual where photographed metaphase
chromosome of a somatic cell are obtained
and arranged in order of decreasing length.
OR
A test to examine chromosomes in a sample
of cells, which can help identify genetic
problems as the cause of a disorder or
disease. This test can count the number of
chromosome and can detect any structural
changes in chromosomes.
64. The test can be performed on almost any
tissue, including:
Amniotic fluid
Blood
Bone marrow
Tissue from the organ that develops
during pregnancy to feed a growing baby
(placenta)
65. This test may be done:
1. On a couple that has a history of
miscarriage
2. To examine any child or baby who has
unusual features or developmental
delays etc
66. Additional conditions under which the test
may be performed:
Ambiguous genitalia
Chronic myelogenous leukemia (CML) or
other leukemia
Developmental delays
Multiple birth defects
67. The bone marrow or blood test can be
done to identify the Philadelphia
chromosome, which is found in about
85% of people with chronic
myelogenous leukemia (CML).
68. Normal Result:
Females: 44 autosomes and 2 sex
chromosomes (XX), written as 46, XX
Males: 44 autosomes and 2 sex
chromosomes (XY), written as 46, XY
69. Abnormal results: May be due to a genetic
syndrome or condition, such as:
Down syndrome
Klinefelter syndrome
Philadelphia chromosome
Trisomy 18
Turner syndrome
This list is not all-inclusive.
70.
71. Isolation of nucleated cell
Culture of that cell in appropriate culture
media
Arrest of cell cycle at metaphase by
adding colchicin.
Separation of dividing cells
Fixation of cells by methanol and glacial
acetic acid
Staining followed by micro-photography.
72.
73. Ploidy: It denotes the no. of chromosomal
set (n) in a cell.
One set of chromosome: It means 23
chromosomes selecting one from each of 23
pairs of homologous chromosomes. It is
symbolized as “n”
Euploidy: An exact multiple of the haploid
chromosome number (n). For example: 2n,
3n, 4n….
74. Aneuploidy: An irregular no. of
chromosomes, not an exact multiple of
haploid no. It involves loss/gain of
chromosome.
Polyploidy: An exact multiple of “n” ,
except 2n. For example: 3n, 4n….
Somy: No. of copy of individual
chromosome. For example: Trisomy 21.
75. A permanent change in the nucleotide base
sequence of the DNA involving coding or non
coding region , regardless of its functional
consequences.
It may be of 3 types :
Genomic mutation
Chromosomal mutation
Gene mutation
76.
77. Cause:
Unrepaired damage to DNA (typically
caused by radiation or mutagens)
Errors in the process
of replication/recombination events of
DNA
Spontaneous change, for example, by
depurination, deamination, etc
78. Genomic mutation: Characterized by alteration
of chromosome number in the genome due to
loss or gain of total chromosome. i.e.
Polyploidy, Aneuploidy
Chromosomal mutation: Characterized by
microscopically detectable gross structural
changes of chromosome . For example:
deletion, duplication, translocation, inversion,
etc.
There may be autosomal mutation/ sex
chromosomes mutation.
79.
80. Gene mutation: Characterized by
submicroscopic alteration of 1/small no.
of bases .
It is of 4 types:
Point mutation
Frame shift mutation
Mutation by deletion/insertion of
3/multiple of 3 bases
Triplet repeat mutation.
81.
82. Missense mutation example: Sickle cell
anemia (glutamate at 6th position is replaced
by valine leading to defective globin chain
synthesis)
Nonsense mutation example: Beta
thalassemia (in beta chain gene of
hemoglobin, glutamate is mutated to stop
codon, UAG. So, a truncated beta chain is
synthesized which is rapidly degraded)
83. Conservative mutations: Result in an amino
acid change. However, the properties of the
amino acid remain the same (e.g.
hydrophobic, hydrophilic, etc)
Non-conservative mutations: Result in an
amino acid change that has different
properties than the wild type (a strain,
gene, or characteristic that prevails among
individuals in natural conditions, as distinct
from an atypical mutant type)
84. A genetic mutation caused
by insertions or deletions of a number
of nucleotides in a DNA sequence that is
not divisible by three (i.e. 1/2/>2 but never
3/multiples of 3)
Due to the triplet nature of gene
expression by codons, the insertion or
deletion can change the reading frame (the
grouping of the codons).
85.
86. Altered reading frame of codon leads to the
gross alteration of amino acid sequences &
composition in its protein from the site of
mutation onward.
Sometimes, altered reading frame can create a
stop codon somewhere to cause premature
termination of protein synthesis.
The resultant protein has alteration in its amino
acid composition, activity, function & stability.
87. Here reading frame of gene is not altered
beyond the site of mutation.
Reading frame of the codon, at definite
short segment of gene , may be changed
leading to insertion of new polypeptide
chain in the resultant protein
or
it may create a stop codon to cause
premature termination of protein synthesis
with truncated protein production.
88. abc def ghi jkl mno pqr
abc d↑ef ghi jkl mno pqr
(↑-> insertion of 3 bases)
abc dxy zef ghi jkl mno pqr
(Reading frame is changed only in
red segment)
89.
90. A normal gene has amplification of sequence
of 3 nucleotides.
Amplification happens during gametogenesis
and gradual expansion occurs down through
generation.
At the stage of full mutation, gene becomes
hugely bulky leading to impaired gene function.
Example: fragile- X- syndrome.
91. Gain of function mutation: Expression of
new function / increased expression of
normal gene function by the mutant
gene.
Loss of function mutation : Expression of
less/no activity by mutant gene &
reduction/absence of gene product
92. Source of all genetic variation
Adaptation to changing environment
leading to long survival of species
Evolution
Pathogenic, so harmful
93. Any agent that is capable of altering a
cell's genetic makeup by changing the
structure of the hereditary
material, DNA.
As many mutations cause
cancer, mutagens are therefore also
likely to be carcinogens.
94. Many forms of electromagnetic radiation
(e.g., cosmic rays, X rays, ultraviolet
light) are mutagenic, as are various
chemical compounds.
95.
96. Not all mutations are caused by
mutagens: so-called "spontaneous
mutations" occur due to
spontaneous hydrolysis, errors in DNA
replication, repair and recombination.
97. Gene expression is the process by which
information from a gene is used in the
synthesis of a functional gene product.
These products are often proteins, but in
non-protein coding genes such as transfer
RNA (tRNA) or small nuclear RNA
(snRNA) genes, the product is a
functional RNA.
It starts at DNA level & ends with synthesis
of protein/peptide.
