Genetics is the study of heredity and genetic variation. It involves DNA, genes, chromosomes, and the mechanisms by which characteristics are passed from parents to offspring. DNA carries the genetic information in cells and is made up of nucleotides with four bases - adenine, thymine, cytosine and guanine. Genes are sections of DNA that code for specific proteins. Chromosomes package and carry the DNA, and genes determine traits by dictating which proteins are produced. Genetic information flows from DNA to RNA to proteins through the processes of transcription and translation.

1. Genetics

2. WHAT IS GENETICS?????
■ The branch of biology that deals with
heredity, especially the mechanisms of
hereditary transmission and the
variation of inherited
characteristics among
similar or related
organisms

3. ■“ Genetics is that branch of
biological sciences which deals
with the transmission of
characteristics from parent to off
spring.”

4. What Is DNA?
■ DNA (deoxyribonucleic acid) carries the
genetic information in the body’s cells.
■ DNA is made up of four similar chemicals
(called bases and abbreviated A, T, C, and
G) that are repeated over and over in pairs.
■ Adenosine, Thymine, Cytosine, Guanine

5. DNA
• Genes are composed mainly of very long strands of DNA; the
total length of DNA in each cell is about a metre.
• Because this is packaged into chromosomes, which are
micrometres (10−6 m) long, this means that the DNA must be
tightly wrapped up to condense it into such a small space.
• DNA is a double-stranded molecule, made up of two chains of
nucleotides.
• Nucleotides consist of three subunits: • a sugar • a phosphate
group • a base.
• The DNA molecule is sometimes likened to a twisted ladder,
with the uprights formed by alternating chains of sugar and
phosphate units

6. DNA
• In DNA, the sugar is deoxyribose, thus DNA.
• The bases are linked to the sugars, and each base binds to
another base on the other sugar/phosphate chain, forming the
rungs of the ladder.
• The two chains are twisted around one another, giving a double
helix (twisted ladder) arrangement.
• The double helix itself is further twisted and wrapped in a highly
organised way around structural proteins called histones, which
are important in maintaining the heavily coiled three-
dimensional shape of the DNA.
• The term given to the DNA–histone material is chromatin.
• The chromatin is supercoiled and packaged into the
chromosomes shortly before the cell divides.

7. Functions of DNA
•DNA is not only responsible for storing genetic
information, but they perform several other functions as
well. These include-
•Replication process: Transferring the genetic information
from one cell to its daughters and from one generation to
the next and equal distribution of DNA during the cell
division.
•Cellular metabolism
•DNA fingerprinting
•Transcription
•Gene therapy
•Mutations

8. Functions of RNA
•RNA is involved in many functions and is found
easily in living organisms, including viruses, plants,
bacteria and animals.
•Here are the primary functions of RNA-It
promotes DNA translation into proteins
•It acts as an adapter molecule during protein
synthesis
•It functions as a messenger between ribosomes
and DNA
•RNA is termed as the carrier of all genetic
information

9. What Is Gene?
■ Ageneisthebasicphysicalandfunctionalunitofheredity.
■ Along the length of the chromosomes are the genes.
Each gene contains information in code that allows
the cell to make (almost always) a specific protein,
the so-called gene product.
■ Each gene codes for one specific protein, and
research puts the number of genes in the human
genome at between 25 000 and 30 000.
■ Genes normally exist in pairs, because the gene on
one chromosome is matched at the equivalent site
(locus) on the other chromosome of the pair

10. Structure of gene
• The structure of gene consists of many elements of which the actual
protein coding sequence is often only a small part. These include DNA
regions that are not transcribed as well as untranslated regions of the
RNA.
• All genes contain a regulatory sequence which is required for their
expression.
• In order to be expressed, genes require a promotor sequence.
• The promotor is recognized and bound by transcription factors and
RNA polymerase to initiate transcription.
• In addition genes can have regulatory regions upstream or downstream
to the open reading frame. These act by binding to transcription factors
which then cause the DNA to loop so that the regulatory sequence
becomes close to RNA polymerase binding site.
• There are enhancer or silencer regions in a gene.
• Enhancer inc. transcription by binding an activator protein which then
helps to recruit the RNA polymerase to the promotor.

11. • Conversely, silencer bind repressor proteins and make
the DNA less available for RNA polymerase.
• The transcribed pre – m RNA contains untranslated
regions at both ends which contain a ribosome binding
site, terminator , and start and stop codons.
• In addition open reading frames contain untranslated
introns which are removed before exons are translated.
• The sequences at the end of the introns dictate the splice
sites to generate the final mature m-RNA which encodes
the protein or RNA product.

13. Functions of genes
• Gene expression :
The process of producing a biologically functional molecule
of either RNA or protein is called as gene expression and
the resulting molecule is called a gene product.
• Genetic code:
The nucleotide sequence of gene’s DNA specifies the amino
acid sequence of a protein through the genetic code. Sets
three nucleotide called as codon
• Transcription
• Translation
• Regulation
• RNA Genes
• Genome

14. ALLELE
■ alleles are pairs or series of genes on a
chromosome that determine the hereditary
characteristics.. An example of an allele is
the gene that determines hair color.

15. ■ Adominant allele produces a
dominant phenotype in
individuals who have one copy of
the allele, which can come from
just one parent.
■ For a recessive allele to produce a
recessive phenotype, the
■
individual must have two copies,
one from each parent.
An individual with one dominant
and one recessive allele for a
gene will have the dominant
phenotype. They are generally
considered “carriers” of the
recessive allele: the recessive
allele is there, but the recessive
phenotype is not.

16. ■ Aphenotype (from Greek phainein,
meaning "to show", and typos, meaning
"type") is the composite of an organism's
observable characteristics or traits, such as
its morphology, development, biochemical
or physiological properties, phenology,
behavior, and products of behavior (such as
a bird's nest).

19. ■ Homozygous-an organism in which 2 copies of
genes are identical i.e. have same alleles
■ Homozygous means you carry two genes that are
the same for each trait. Example: BB for brown
eyes.
■ Heterozygous-an organism which has different
alleles of the gene or Heterozygous means you
carry two different genes for each trait
Heterozygous-an organism which has different
alleles of the gene
■ Example: Bb would also be brown eyes, though the
small "b" would be the gene forblue eyes. It
doesn't show up in the phenotype (outward
appearance) because the gene for brown eyes is
dominant. If someone had blue eyes they would be
homozygous "bb".

20. Homozygous and Heterozygous
■ Here BB & bb is the homozygous and Bb is
the heterozygous

22. What Are Chromosomes?
■
■
word chromosome is derived
from the Greek words
“chromo” meaning colour
and “soma” meaning body.
Humans have 23 pairs of
chromosomes (for a total of
46).
■
■
Of those, 1pairis the sex chromosomes
(determines whether you are male or female),
and
the other 22 pairs are autosomal
chromosomes (determine the rest of the

23. • Each chromosome is one of a pair, one inherited from
the mother and one from the father, human cell has 46
chromosomes that can be arranged as 23 pairs.
• A cell with 23 pairs of chromosomes is termed diploid.
Gametes (spermatozoa and ova) with only half of the
normal complement, i.e. 23 chromosomes instead of 46,
are described as haploid.
• Chromosomes belonging to the same pair are called
homologous chromosomes.
• The complete set of chromosomes from a cell is its
karyotype

24. Cont..
• Each pair of chromosomes is numbered, the largest pair
being no. 1.
• The first 22 pairs are collectively known as autosomes,
and the chromosomes of each pair contain the same
amount of genetic material.
• The chromosomes of pair 23 are called the sex
chromosomes because they determine the individual’s
gender.
• Unlike autosomes, these two chromosomes are not
necessarily the same size; the Y chromosome is much
shorter than the X and is carried only by males.
• A child inheriting two X chromosomes (XX), one from
each parent, is female, and a child inheriting an X from

25. • Each end of the chromosome is capped with a length of
DNA called a telomere, which seals the chromosome and
is structurally essential.
• During replication, the telomere is shortened, which
would damage the chromosome, and so it is repaired
with an enzyme called telomerase.
• Reduced telomerase activity with age is related to cell
senescence

26. Chromosomes:
■ Chromatin: made up of DNA, RNA &
proteins that make up chromosome,
Chromatin is located in the
nucleus of a cell.
• Chromatin fibers
become coiled into
chromosomes
■ Chromatids: one of the two identical
parts of the chromosome.
■ Centromere: the point where two
chromatids attach

29. Functions of chromosome
•Chromosomes assist in the growth of reproduction,
regeneration and repair process, which is an essential
survival element.
•The ultrastructure of the chromosome prevents
deoxyribonucleic acid or DNA coils from being damaged
and intertwined.
•Transferring genetic material from one peer group to
another is the primary function of chromosome cells.
•The chromatids that connect with the centromere
support the motion of chromosome cells at the time of
cell division.
•Chromosomes have thousands of genes that directly
provide codes for various proteins adjacent to living

30. Cont..
•As chromosomes hold the deoxyribonucleic acid
tightly and deliver proteins in eukaryotic cells, they
are called “packaging material”.
•Chromosomes play an essential role in replication,
cell division, and the creation of daughter cells as
the ultrastructure chromosome helps separate
copies by creating new complete sets

31. ■ NUCLEOTIDE: group of molecules that when
linked together, form the building blocks of DNA
and RNA; composed of phosphate group, the
bases: adenosine, cytosine, guanine and thymine
and a pentose sugar. In case of RNA, thymine base
is replaced by uracil.
■ CODON: series of three adjacent bases in one
polynucleotide chain of a DNA or RNA molecule
which codes for a specific amino acid.
■ GENETIC CODE: the sequence of nucleotides in
a DNA or RNA molecule that determines the
amino acid sequence in the synthesis of proteins.

32. ■ Aseries of codons in part
of amRNA molecule. Each
codon consists of three
nucleotides, usually
representing a single
amino acid.
■ The nucleotides are
abbreviated with the letters
A, U, G and C. This is
mRNA, which uses U (
uracil). DNA uses T (
thymine) instead.

33. Protein synthesis
• Protein synthesis is the process in which cells make proteins. It
occurs in two stages: transcription and translation.
• In eukaryotic cells, transcription takes place in the nucleus.
• During transcription, DNA is used as a template to make a
molecule of messenger RNA (mRNA).
• The molecule of mRNA then leaves the nucleus and goes to a
ribosome in the cytoplasm, where translation occurs.
• During translation, the genetic code in mRNA is read and used to
make a polypeptide. These two processes are summed up by the
central dogma of molecular biology: DNA → RNA → Protein.

34. Transcription
• Transcription is the first part of
the central dogma of molecular
biology: DNA → RNA.
• It is the transfer of genetic
instructions in DNA to mRNA.
• During transcription, a strand of mRNA
is made to complement a strand of DNA.

36. Process of Transcription
• During transcription, a strand of mRNA is synthesized from a
particular gene template.
1.Transcription factor binds to promoter region.
• A transcription factor binds to a promoter of a particular gene.
The binding of a transcription factor to a promoter leads to the
recruitment of several key enzymes and proteins to the gene.
2.DNA helicase unwinds the gene region
• DNA helicase unwinds the gene region by breaking the
hydrogen bonds between the two strands of DNA. This exposes
the bases on each strand. The two unwound strands of DNA are
referred to as either the coding strand or the template strand.
This strand is also sometimes known as antisense DNA.

37. CONT..
3.Enzyme RNA polymerase binds.
• The enzyme RNA polymerase binds in a region
just before the start codon of the gene.
4.RNA polymerase transcribes the mRNA.
• RNA polymerase reads the nucleotides on the
unwound template (antisense) strand of DNA.
It then recruits nucleotides and continually
makes a strand of RNA. The growing mRNA
strand lengthens in the 5’ to 3’ direction.
5.RNA polymerase reaches the stop codon.
• RNA polymerase stops transcribing mRNA once
it reaches the stop codon.
6.The resulting strand of RNA is known as pre-
mRNA. The pre-mRNA will have the complimentary
sequence to the coding strand, except all
thymine bases will be replaced with uracil

39. • Post-Transcription
Splicing
In prokaryotes,
transcription directly
leads to an mRNA.
However, in eukaryotes,
transcription makes pre-
mRNA, which then has to
be spliced to make mRNA..

40. RNA Splicing
RNA Splicing
•The pre-mRNA contains both exons and
introns. Before the mRNA can go to the
ribosomes, the introns need to be removed. This
way, the final mRNA only has the exons which
contain the codons for the ribosomes to read.
•Splicing forms a spliceosome. Splicing is
carried out by specialised proteins that form a
structure known as the spliceosome. The
spliceosomes recognise where an intron starts
and where an intron ends. They then attach to
this region and cut them out of the pre-mRNA.
They then join the exons together.
•Finally an mRNA is made. Following 5’ capping,
poly A-tail formation and splicing, an mRNA is
made. This mRNA is then ready to travel out of

41. Cont.
Splicing removes introns from mRNA, Introns are regions
that do not code for the protein. The remaining mRNA
consists only of regions called exons that do code for the
protein. The ribonucleoproteins are small proteins in the
nucleus that contain RNA and are needed for the splicing
process.
Editing changes some of the nucleotides in mRNA. For
example, a human protein called APOB, which helps
transport lipids in the blood, has two different forms
because of editing. One form is smaller than the other
because editing adds an earlier stop signal in mRNA.
5’ Capping adds a methylated cap to the “head” of the
mRNA. This cap protects the mRNA from breaking down, and
helps the ribosomes know where to bind to the mRNA
•Polyadenylation : adds a “tail” to the mRNA. The tail
consists of a string of As (adenine bases). It signals the
end of mRNA. It is also involved in exporting mRNA from the

43. Translation
Translation occurs in three stages: Initiation,
Elongation and Termination.
Initiation:
• After transcription in the nucleus, the mRNA
exits through a nuclear pore and enters the
cytoplasm.
• At the region on the mRNA containing the
methylated cap and the start codon, the small
and large subunits of the ribosome bind to
the mRNA.
• These are then joined by a tRNA which
contains the anticodons matching the start
codon on the mRNA. This group of molecules

44. Elongation:
• tRNA keep bringing amino acids to the
growing polypeptide according to
complementary base pairing between the
codons on the mRNA and the anticodons
on the tRNA.
• As a tRNA moves into the ribosome,
its amino acid is transferred to the
growing polypeptide.
• Once this transfer is complete, the
tRNA leaves the ribosome, the ribosome
moves one codon length down the mRNA,
and a new tRNA enters with its

45. Termination:
• At the end of the mRNA coding is a
stop codon which will end the
elongation stage.
• The stop codon doesn’t call for a
tRNA, but instead for a type of
protein called a release factor, which
will cause the entire complex (mRNA,
ribosome, tRNA, and polypeptide) to
break apart, releasing all of the
components.

47. ■ Congenital Disease.
Diseases which are present at birth.
■ Hereditary/Familial Disease.
Diseases which are derived from
one’s parents and transmitted in the
gametes through the generations.
Not all congenital diseases are genetic( congenital
Syphilis) and not all genetic diseases are congenital
(Huntington disease).

48. Mutations.

49. Definition:
■Apermanent heritable change in a
gene or chromosomal structure and are
important in the causation of cancer
and some congenital diseases.

50. CAUSES OF MUTATIONS
■ Chemicals
✓ Nitrous acid
✓ Alkylating agents
✓ 5- bromouracil
✓ Antiviral drug iododeoxy uridine
✓ Benzpyrene in tobacco smoke

51. ■ X – rays & ultraviolet light
■ Certain viruses such as bacterial virus

52. Types Of
Mutations.

53. 1. Point Mutation
2. Deletion
3. Frameshift Mutations
4. Trinucleotide Repeat Mutations

54. 1. Point Mutation:
■ Substitution of a single nucleotide base by a
different base.

56. ■ Sickle cell anaemia is the result
of a point mutation in codon
6 of the b-globin
gene resulting in the substitution
of amino acid glutamic acid by
valine .
■ b-globin is a major component
of adult haemoglobin (HbA).
The single amino-acid
substitution results in a type of
haemoglobin termed HbS, which
has different properties from the
normal HbA. Under conditions of
low oxygen tension, or in an
atmosphere containing a low
oxygen level, the following

57. ■ (1)The haemoglobin agglutinates to form insoluble
rod-shaped polymers;
■ (2)Red blood cells become distorted and sickle-
shaped ;
■ (3)The sickle-shaped cells rupture easily causing
haemolytic anaemia;
■ (4)The sickle shaped cells tend to block capillaries
interfering with the blood flow to various organs.

58. 2. Deletion Mutations:
■ Insertion or deletion of one or more base
pairs alters the reading frame of the DNA
strand.
■ Deletion of one codon causing Cystic
Fibrosis.
■ Deletion of 6 codons in the b-globin gene
resulting in a variant haemoglobin

61. 3. Frame shift mutations
■ Frame shift mutations involve a deletion or insertion
of one or two base pairs within a coding sequence of a
gene.
■
■ As the coding message is read in triplets codons and
deletions the reading frame of mRNA is altered
resulting in a non-sense sequence of amino acids.
An example occurs in the b-globin gene in which one
nucleotide of codon 39 is deleted . The following
reading frame is completely altered and continues
until a stop codon is encountered.
■ Duchenne muscular dystrophy are caused by frame
shift mutations in the dystrophin gene.

62. Deletion

63. Insertion
■ Tay-Sachs disease is a rare inherited disorder that progressively
destroys nerve cells (neurons) in the brain and spinal cord

64. 3. Trinucleotide Repeat
Mutations:
■ Trinucleotides are triplets of nucleotides that are
repeated in tandem many times over. The number of
repeats varies in different individuals.
■ An example of trinucleotide repeats is - - - CAG
CAG CAG CAG CAG - - - -, and is designated as
(CAG)n where n is the number of repeats in the
particular individual.
■ A formof mutation characterized by a stretch of three
nucleotides (codon) repeated in multiple times in the
DNA sequence. e.g. Fragile X Syndrome(developmental
problems including learning disabilities and cognitive impairment. )

66. Classification Of Genetic
Diseases:
■ Single Gene Defects/Mendelian Disorders.
■ Disorders with Multifactorial or Polygenic
inheritance.
■ Cytogenetic Disorders.

67. Single gene disorders/
Mendelian Disorders
Agenetic disease caused by a
single mutation in the structure
of DNA, which causes a single
basic defect with pathologic
consequences

68. According to the Patterns Of
Inheritance, single gene disorders
are:
■Autosomal Dominant Disorder.
■Autosomal Recessive Disorder.
■X-Linked Recessive Disorder.
■X-Linked Dominant Disorder.

69. Autosomal
Dominant
Disorders.

70. The pedigree on the right illustrates the
transmission of an autosomal
dominant trait.
Affected males and females have an
equal probability of passing on the
trait to offspring.
Affected individual's have one normal
copy of the gene and one mutant
copy of the gene, thus each offspring
has a 50%chance on inheriting the
mutant allele.
As shown in this pedigree,
approximately half of the children of
affected parents inherit the
condition and half do not.
■ Individuals with these diseases
usually have one affected parent .*
■ Autosomal Dominant
Conditions:
• Huntington Disease
•Acondroplasia (short-
limbed dwarfism)
•polycystic kidney
disease

71. Inheritance Pattern:
•Typical mating pattern is
a heterozygous affected
individual with a
homozygous
unaffectedindividual.
•Both sexes are
affected equally..

72. Marfan’s Syndrome:
genetic disorder that affects the body's
connective tissue.
▪ Mutation in the fibrillin gene.
▪Fibrillin important component of
microfibrils in Elastin.
Tissues affected are Skeleton, Eyes and
the CVS.
▪it include tall stature, long fingers,
pigeon breast deformity, hyper-
extensible joints, high arched palate, BL
subluxation of lens, floppy Mitral valve,
Aortic aneurysm and dissection, defects
in skin, lungs.

73. ■What is Fibrillin?
■ Marfan syndrome is caused by changes in fibrillin
genes. Fibrillin is a glycoprotein, which is essential
for the formation of elastic fibers or microfibrils that
provide strength and flexibility to connective tissue.
■ Connective tissue holds the body together and helps
control the growth and repair of tissues and organs.
■ Fibrillin normally is abundant in the connective
tissue found in the aorta, in the ligaments that hold
the eye's lenses in place, in the bones and the lungs.

74. ■ How is Fibrillin related to Marfan syndrome?
■ Marfan syndrome is caused by changes (mutations)
in one member of the pair of fibrillin genes. As a
result, the body produces fibrillin that does not
work and connective tissue that is not as strong as it
should be.
■ The growth and development of the body are
affected, particularly in the connective tissues of the
aorta, eye and skin.
■ It causes overgrowth of the long bones of the body,
resulting in tall height, long arms and legs, and a
weakened structural support in blood vessels, heart
valves, cartilage and ligaments.

75. Ehler-Danlos Syndrome(Cutis
Hyperelastica):
■ Characterized by defects in collagen
synthesis/connective tissue.
■ Clinical Features include fragile, hyper-extensible
skin, hyper-mobile joints, rupture of internal
organs like the colon, cornea and large arteries,
poor wound healing.

77. Autosomal
Recessive
Disorders

78. ■ Recessive conditions are clinically
manifest only when an individual has
two copies of the mutant allele.
■ When just one copy of the mutant
allele is present, an individual is a
carrier of the mutation, but does not
develop the condition.
■
■
Females and males are affected
equally by traits transmitted by
autosomal recessive inheritance.
When two carriers mate, each child
has a 25%chance of being
homozygous wild-type (unaffected); a
25%chance of being homozygous
mutant (affected); ora 50%chance of
being heterozygous (unaffected
carrier).
■
■
Affected individuals are
indicated by solid black symbols
and unaffected carriers are
indicated by the half black
symbols.
Autosomal recessive diseases:
• Cystic fibrosis
• Tay-Sachs
• hemochromatosis
• phenylketonuria (PKU)

79. Pattern Of Inheritance:
▪Typical mating pattern is two
heterozygous unaffected
(carrier) individuals.
The trait doesnot usually affect
the parent, but siblings may
show the disease
Siblings have one chance in
four of being affected
▪ Both sexes affected equally.

80. Disorders:

81. X-Linked
Recessive
Disorders.

82. ■ Most common X-linked
disorders.
■
■
Usually expressed only in males.
Rarely, due to random X-
inactivation, a female will express
disease, called manifesting
■
heterozygotes.
An unaffected woman carries one
copy of a gene mutation for an X-
linked recessive disorder. She has
an affected son, an unaffected
daughter who carries one copy of
the mutation, and two unaffected
children who do not have the
mutation.

83. Pattern Of
Inheritance:
•Disease usually passed on
from carrier mother.
•Expressed in male offspring,
females are carriers.
•Skipped generations are
commonly seen.
•In this case, Recurrence risk
is half of sons are affected,
half of the daughters are
carriers.

84. Recurrence risk:
All the daughters are
erozygous carriers and all
sons are homozygous
normal.
a man is affected with an l
inked recessive
ndition, all his daughter
l inherit one copy of the
tant allele from him.

85. Disorders:

86. X-linked Dominant
Disorder

87. ■ Because the gene is located on
the X chromosome, there is no
transmission from father to son,
but there can be transmission
from father to daughter (all
daughters of an affected male
will be affected since the father
has only one X chromosome to
transmit).
■ Children of an affected woman
have a 50%chance of inheriting
the X chromosome with the
mutant allele.
■ X-linked dominant disorders are
clinically manifest when only
one copy of the mutant allele is
present.
X.linked Dominant Disorders
•some forms of retinitis
pigmentosa
•Chondrodysplasia
Punctata
•hypophosphatemic
rickets

88. DISORDERS WITH
MULTIFACTORIAL
(POLYGENIC)INHERITANCE
■ Multifactorial inheritance, also called complex
or polygenic inheritance.
■ Polygenic inheritance occurs when one
characteristics is controlled by 2 or more
genes eg:height,skin colour,eye color, weight.
■ P.I is defined as quantitative inheritance where
multiple independent genes have an additive
or similar effect on single quantitative trait.

89. ■ Multifactorial inheritance disorders are caused
by a combination of environmental factors and
mutations in multiple genes(genetic factor).
For example, different genes that influence
breast cancer
■ susceptibility have been found on
chromosomes 6, 11, 13, 14, 15, 17, and 22.
Some common chronic diseases are
multifactorial disorders.

90. ■ Rate of recurrence is 2 to 7%

91. COMMON DISEASES ASSOCIATED with DISORDERS WITH
MULTIFACTORIAL INHERITANCE
■ Diabetes mellitus
■ Hypertension
■ Gout
■ Cleft lip and palate
■ Schizophrenia
■ Bipolar disorder
■ Congenital heart disease
■ Skeletal abnormalities
■ Neural tube defects
■ Coronary artery disease

92. Cytogenetic
Disorders.

93. ■Cytogenetic disorders may result
from structural or numeric
abnormalities of chromosomes
■It may affect autosomes or sex
chromosomes

94. Numeric Abnormalities:
■ Normal Chromosomal number is 46. (2n=46). This
is called euploidstate. (Exact multiple of haploid
number).
■ Poly
ploidy
: posession of more than two sets of
homologous chromosomes. Chromosomal numbers
like 3n or 4n. (Incompatible with life); generally
results in spontaneous abortion
■ Aneuploidy
:Any Chromosomal number that is not
an exact multiple of haploid number . E.g 47 or 45.

95. Aneuploidy:
■ Most common cause is
nondisjunction (attach)of
either a pair of homologous
chromosomes during
meiosis I or failure of sister
chromatids to separate
during meiosis II.
■ The resultant gamete will
have either one less
chromosome or one extra
chromosome.

96. ■Fertilization of such gamete will
result in zygote being either trisomic
( 2n+1 ) ormonosomic ( 2n-1 ).
■Monosomy in autosomes is
incompatible with life.
■Trisomy of certain autosomes and
monosomy of sex chromosomes is
compatible with life.

97. Mosaicism:
■ Aperson ora tissue that contains two ormore
types of genetically different cells.
■ Mosaicism is caused by an error in cell division
very early in the development of the unborn baby.
■ Examples of mosaicism include:
■ Mosaic Down Syndrome
■ Mosaic Klinefelter Syndrome
■ Mosaic Turner Syndrome

98. Structural Abnormalities:
■ Usually result from chromosomal
breakage, resulting in loss or
rearrangement of genetic material.
■ Patterns of breakage:
•
•
•
•
•
Translocation.
Isochromosomes.
Deletion.
Inversions.
Ring Chromosomes.

99. TRANSLOCATION
■ when a part of one chromosome is transferred
to another chromosome
■ Translocations are indicated by t
■ E.g. 46,XX,t(2;5)(q31;p14)
■ There are two type of translocation.
1. In a reciprocal translocation,
segment from two different
chromosomes have been
exchanged

100. 2. Centric fusion type or robertsonian
translocation:
✓ The breaks occur close to the centromere, affecting
the short arms of both choromosomes
✓ Transfer of the chromosome leads to one very large
and one extremely small chromosome
✓ The short fragments are lost, and the carrier has 45
chromosomes
✓ These occur with chromosomes 13, 14, 15, 21, and
22
✓ Such loss is compatible with survival

102. ISOCHROMOSOMES
■ Result when one arm of a chromosome is lost and the
remaining arm is duplicated, resulting in a chromosome
consisting of two short arms only or of two long arms.

103. DELETION
■ Loss of a portion of chromosome
■ This can be terminal (close to the end of the
chromosome on the long arm or the short
arm), or it can be interstitial (within the long
arm or the short arm).
■ Aring chromosome is a variant of deletion.It
occurs when break occurs at both the ends
of chromosome with fusion of the damaged
ends.

104. INVERSIONS
■ A portion of the chromosome has broken off ,
turned upside down and reattached, therefore
genetic material is inverted.
■ Occur when there are two breaks within a single
chromosome with inverted reincorporation of the
segment.
■ Since there is no loss orgain of chromosomal
material, inversion carriers are normal.
■ An inversion is paracentric if the inverted segment
is on the long arm or the short arm .
■ The inversion is pericentric if breaks occur on both
the short arm and the long arm .

107. ■Ring Chromosome
■ Aportion of a chromosome has broken off
and formed a circle or ring . This can
happen with or without loss of genetic
material.

108. General Features of Cytogenetic Disorders:
■Associated with absence, excess, or
abnormal rearrangements of
chromosomes.
■Loss of genetic material produces more
severe defects than does gain.
■Abormalities of sex chromosomes
generally tolerated better than those of
autosomes.

109. ■Sex chromosomal abnormalities are
usually subtle and are not detected at
birth.
■Most cases are due to de novo changes
(i.e. parents are normal and recurrence
in siblings is low).
■ Defn of de novo change: An alteration in a gene that is present
for the first time in one family member as a result of a mutation
in a germ cell (egg or sperm) of one of the parents or in the

110. Cytogenetic
Disorders involving
Autosomes.

111. Trisomy 21/Down’s Syndrome:
■Most common chromosomal disorder.
■Down syndrome is a chromosomal
abnormality characterized by the
presence of an extra copy of genetic
material on the 21stchromosome
■Trisomy 21 is caused by a meiotic
nondisjunction (attach) event.

112. ■ With nondisjunction, a gamete (i.e., a sperm
or egg cell) is produced with an extra copy of
chromosome 21;the gamete thus has 24
chromosomes
■ When combined with a normal gamete from
the other parent, the embryo now has 47
chromosomes, with three copies of
chromosome 21.
■ About 4%of cases are due to Robertsonian
translocations.
■ Maternal age has a strong influence

113. Karyotype for trisomy Down syndrome. Notice the three copies of
chromosome 21

114. Other Trisomy Syndromes:
■Trisomy 18 : Edwards Syndrome.
■Trisomy 13 : Patau Syndrome.

115. Cytogenetic Disorders
involving Sex
Chromosomes

116. ■Extreme karyotypic variations seen
frequently with Sex Chromosomes, with
females having 4-5 extra X Chromosomes.
■Males with 2 to 3 Ychromosomes have also
been identified.

117. Klinefelter’s Syndrome:
■Defined as Male Hypogonadism (doesnot
produce enough testosterone), develops when
there are at least two X chromosomes
and one ormore Ychromosomes.
■Usual karyotype is 47,XXY. The extra X
may be maternal or paternal.
■ Akaryotype (Greek karyon = kernel, seed or nucleus) is
the number and appearance of chromosomes in the
nucleus of a eukaryotic cell.

118. ■Results from nondisjunction of sex
chromosome during meiosis.
■Risk factors include advanced maternal
age and a history of exposure to
radiation in either parent.

119. Clinical Manifestations:
■ Increase in body length between soles and
pubis.
■ Reduced facial, body and pubic hair.
Gynecomastia.(swollen male breast
tissue due to reduced male
hormones.
■ Testicular atrophy.
■ Infertility.
■ Mild mental retardation.

120. Turner Syndrome:
■Primary hypogonadism in females
■Results from partial or complete
monosomy of the X chromosome.

121. ■Most common cause is absence of one
X chromosome.
■Less commonly, mosaicism(addition no. of
chromosome), or deletions on the short
arm of the X chromosome.

123. Question bank
10 marks :
1. Write a note on genetic disorder / genetic pattern of
inheritance.
2. Enlist genetic disorder. And explain cytogenetic
disorder with one example of disease.
3. Discuss in detail about protein synthesis.
5 marks.
1.Discuss about gene and its function.
2. Explain DNA and its function
3. Write a note on chromosome.
4. Discuss about single gene disorder.
5.Explain marfan’s syndrome.

124. Cont..
2 marks.
1. Define : genetics, multifactorial inheritance
• down syndrome,
• Klinefelter syndrome ,
• Huntington Disease
•Acondroplasia
•Mutation
2. Write functions of : GENE, DNA, Chromosome
3. Enlist different types of genetic pattern of
inheritance

125. THANK YOU