The document discusses genetic disorders, defining them as congenital diseases caused by mutations in DNA or chromosomes. It describes various types of genetic disorders including single gene disorders, multifactorial disorders, and chromosomal disorders, detailing inheritance patterns and examples for each type. Additionally, it outlines the mechanisms of mutations and their categories, providing references for further reading.

1. Dr. G. Shanmugavel,
Assistant Professor of Biology ,
Department of HSS,
Puducherry Technological University
Email : shanmugavel.g@ptuniv.edu.in

2. Genetic disorder
• Disorder or disease is any deviation from the normal structure
and function of the body, which are transmitted from one
generation to next generation are called genetic disorder or
genetically transmitted disease.
• Genetic disorders are congenital disease i.e. disease condition
that occur during intrauterine life.
• Genetic disorder also called as birth defects.
• Genetic disorder caused by changes in the structure or
number of DNA sequence and chromosome mainly due to
mutation.
• It can be caused by a mutation in a single gene (monogenic)
or multiple genes (polygenic) or by a chromosomal
abnormality.

3. Mutation
• Mutation is a heritable change in the structure of a gene or
chromosome or a change in chromosome number.
• Mutation is an alternation in the nucleotide sequence of the
genome of an organism, virus or extrachromosomal DNA.

4. Mutation causing agents

5. Mutations are categories into of three classes:
Gene mutation
– Changes occurs in the gene (DNA sequence) is
known as gene mutation or point mutation.
Chromosomal mutation
– Structural changes occurs in the chromosome is
called as chromosomal mutation.
Genomic mutations
– Variation in chromosome number of a whole
genome is known as genomic mutations.

6. Types of genetic disorders
1. Single gene disorder
• Autosomal dominant disorder
• Autosomal recessive disorder
• Sex-linked inheritance
– X linked disorder
– Y linked disorder
2. Multifactorial disorder
3. Chromosome disorder

7. Single gene inheritance
• Single gene inheritance is also called
Mendelian or monogenetic inheritance.
• Changes or mutations that occur in the DNA
sequence of a single gene cause this type of
inheritance.
• There are thousands of known single-gene
disorders. These disorders are known as
monogenetic disorders (disorders of a single
gene).

8. Autosomal dominant disorder
• Autosomal dominant disorders occur when only one
mutated gene in a pair of chromosome is sufficient to
cause disease.
• Mutated genes are dominant over their alleles in this
category of disorders. Such disorders are inherited like
typical Mendelian dominant characters.
• An essential feature of a dominantly inherited disorder
is that it is always present in at least one parent in each
ancestral generation.
• Some common dominant defective traits are
Polydactyly, Achondroplastic dwarfism, Huntington's
chorea and Opalescent teeth.

9. Autosomal dominant
Polydactyly

10. Autosomal dominant
Achondroplasia
 The most common form of short-limbed dwarfism

12. Autosomal recessive disorder
• Both chromosomes in a pair must have a mutated
gene that could cause a genetic disorder.
• If only one chromosome has a mutated gene, the
person is a carrier and does not have symptoms.
• These disorders are expressed only in a
homozygous condition.
• Major autosomal recessive disorders are Sickle
cell anemia, Phenylketonuria, Albinism,
Tay - Sachs disease, Cystic fibrosis, etc

13. Albinism
Photo Source: Wikipedia, The Economic times

14. Cystic fibrosis

16. Sex-linked disorder
• Disorders caused by mutated genes that are
located in sex chromosomes.
• The pattern of inheritances for sex-linked
differ from autosomal, because male and
female differ in their sex chromosomes.
• Based on the location of mutated gene in sex
chromosome, it classified as X-linked and Y
linked.

17. X-linked disorder
• Mutated genes located on the X chromosome cause
determine X-linked disorder.
• X-linked disorders are predominately inherited because
it presence in both the sex (Female - XX; Male - XY).
• X-linked disorders are more common in men than
women due to their X-linked inheritance pattern.
• X-linked disorders are categories into dominant and
recessive traits.
• In human, color blindness, hemophilia, muscular
dystrophy, fragile-X syndrome, etc. are X-linked
disorder.

18. X-linked disorder
• X-linked dominant disorder
– Fragile-X Syndrome
– Goltz syndrome
– X-linked dominant porphyria
• X-linked recessive disorder
– Color blindness
– Hemophilia
– Duchenne muscular dystrophy

19. Color blindness

20. Hemophilia

22. Y-linked disorder
• Mutated genes located on the Y chromosome cause Y-linked
disorder. It is also known as holandric inheritance.
• These disorders are present only in males, because only males
possess a Y chromosome. Thus, it can only pass from father to
son.
• In human, Y-linked disorder
– Hypertrichosis of the ears
– Webbed toes
– Male infertility

23. Hypertrichosis or hair pinna of the ears
Photo Source: Internet

24. Webbed toes
Photo Source: Internet

25. Multifactorial disorder
• Multifactorial disorders are caused by a
combination of mutations in multiple genes and
environmental factors.
• It is also called as complex or polygenic disorder.
• The genetic mechanisms underlying these
disorders are not well understood.
• Alzheimer disease, Bipolar disorder, Cleft lip or
palate, Neural tube defects, Diabetes,
hypertension, etc. are multifactorial disorder.

26. Multifactorial inheritance
• Birth defects such as neural tube defects and cleft palate
• Cancers of the breast, ovaries, bowel, prostate, and skin
• High blood pressure and high cholesterol
• Diabetes
• Alzheimer disease
• Schizophrenia
• Bipolar disorder
• Arthritis
• Osteoporosis
• Skin conditions such as psoriasis, moles, and eczema
• Asthma and allergies
• Multiple sclerosis and other autoimmune disorders

27. Chromosomal disorder
(Chromosomal abnormality)
• Abnormalities in chromosome number or structure can
result in this disorder.
• This type of abnormality results either loss or addition
of one or more chromosomes.
• It is typically occur due to a problem with cell division,
which leads to euploidy and aneuploidy condition of
chromosome.
• Euploidy is common in plants whereas aneuploidy is
common in animals.
• Examples of chromosomal disorders in humans are
Down syndrome (trisomy 21), Edward’s syndrome
(trisomy 18), Turner syndrome (45, X), Klinefelter
syndrome (47, XXY), etc.

28. Chromosomal abnormalities
• Down syndrome (trisomy 21)
• 45, X (Turner syndrome)
• 47, XXY (Klinefelter syndrome)
• 47, XYY; and 47, XXX
• The major chromosomal aneuploidies seen in
live-born babies are: trisomy 18; trisomy 13.

29. References:
• Concepts of Genetics (9th ed.), W. S. Klug, M. R. Cummings, C.
Spencer, C. A. Spencer, and M. A. Palladino, Pearson, 2008.
• Molecular Genetics (Second edition), Stent, G. S.; and Calender,
R. W.H. Freeman and company, Distributed by Satish Kumar Jain
for CBS Publisher.
• Human genetics : concepts and applications. Lewis, Ricki.
(2007). Boston :McGraw-Hill Higher Education.
• Genetics (9th ed.), Verma PS and Agarwal VK (2010). Publisher:
S Chand & Co Ltd.
• Textbook of PUBLIC HEALTH AND HYGIENE, G Shanmugavel
and Binu George (2021). Publisher: Darshan Publishers.
• Textbook of BIOLOGY FOR ENGINEERS, G Shanmugavel (2024).
Publisher: Lambert academic publishing.