This document provides an overview of genetics and genetic disorders. It defines key genetic terms like DNA, genes, alleles, dominant and recessive genes, genotypes and phenotypes. It discusses different types of genetic disorders like single gene disorders, chromosomal diseases, and multifactorial diseases. Specific chromosomal disorders discussed include Down syndrome, Turner syndrome, and Klinefelter syndrome. The roles of meiosis, mitosis, mutations, and Punnett squares in genetic inheritance are also summarized. Overall, the document concisely introduces many fundamental concepts in genetics.

1. Hakim Shah
RN, BSN, MSN, PhD (Scholar)
30-08-2022
1
Required Reading Book:
Carol, Porth M. (2014). Pathophysiology concept of altered health
states (9th Ed). Philadelphia: J. B. Lippincott.
(Book is available in ICoNM Library)
Chapter-7, Page No. 138-158

2. Class Objectives
• Differentiate between Genetic and congenital disorders
• Define the following terminologies related to genetic
disorder:
– Trisomy
– Monosomy
– Polysomy
• Discuss the chromosomal defects with special emphasis on
aneuploidy
• Describe the pathophysiology and the clinical
manifestations of the following genetic disorders:
– Down’s syndrome
– Turner’s syndrome
– Klienfelters syndrome
2

3. Introduction to Genetics
• “Genetics is the study of heredity, the process
in which a parent passes certain genes onto
their children.”
• Children inherit their biological parents’ genes
that express specific traits, such as some
physical characteristics, natural talents, and
genetic disorders.
3

4. Congenital Diseases
• Those diseases present at birth
• Note that not all genetic diseases present at birth
• Congenital diseases include:
1. Developmental diseases
• Those that arise spontaneously during gestation
• Example: failure of testis to descend
2. Those that are secondary to environmental problems
• From trauma
• From poisons (teratogenic agents)
• From poor nutrition of mother during gestation
4

5. Types of Genetic Disorders
• There are Three types of Genetic Disorders:
1. Single gene disorders
2. Chromosomal diseases
1. Multifactorial diseases
5

6. 1. Single Gene Disorders
This type of genetic disorders occur due to
Nucleotide mutation. Classified by inheritance
pattern
6

7. 2.Chromosomal Diseases
Usually occurs during mitosis
There are 2 types of chromosomal diseases
a. Structural change of the chromosome
• Deletion: cause most serious problems and/or
death
• Translocation: broken part of chromosome
becomes attached to non-homologous
chromosome
7

8. Cont…
b. Change in chromosome number
• Caused during meiosis by nondisjunction
• Euploidy: normal number of
chromosomes
• Aneuploidy: abnormal number of
chromosomes. Example:
– Turner’s syndrome: monosomy X
– Down’s syndrome: Trisomy 21
8

9. 3. Multifactorial diseases
• May be a combination of environmental factors &
genetic tendency.
– Example: Lung cancer, colon cancer
• These may be polygenic.
– Example: deafness, diabetes
9

10. Basic Unit of Genetics: DNA
• DNA is present on Chromosomes in the nucleus
of a cell.
• DNA is made up of four different parts
called nucleotides.
• Nucleotides are set of blocks that has only four
shapes, or an alphabet that has only four letters.
• DNA is a long string of these blocks or letters.
• These blocks or letters (Nucleotides) are the
building block of DNA
10

11. Structure of DNA
• DNA is a long string of Nucleotides.
• Each nucleotide consists of a sugar (deoxyribose) bound on one
side to a phosphate group and bound on the other side to
a nitrogenous base.
• There are two classes of nitrogen bases
• Purines (double-ringed structures)
• Pyrimidines (single-ringed structures)
• The four bases in DNA's alphabet are:
• Adenine (A) - a purine
• Cytosine(C) - a pyrimidine
• Guanine (G) - a purine
• Thymine (T) - a pyrimidine"
• Adenine pairs with thymine and cytosine pairs with guanine.
• DNA comes in a shape known as double helix, which is basically a
twisted ladder. 11

12. 12

13. 13

14. Basic Concepts of Genetics
• Gregor Johan Mendel is known as the “father
of Genetics”.
• He was born on July 20, 1822 in Austria and
was died on January 6, 1884.
• He laid the foundation of Genetics by working
with seven characteristics of pea plants: plant
height, pod shape and color, seed shape and
color, and flower position and color.
14

15. Principle of Independent Assortment
• During his experiment with the seven characteristics
of pea plan, Gregor Mendel found out:
Inheritance of one trait has no effect on the
inheritance of another trait.
• This is called principle of independent assortment.
15

16. Traits
• Traits are determined by the genes on the
chromosomes.
• Genetics is the study of how traits are passed
from parent to offspring
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17. Traits
17

18. Genes
• Genes are the segments of DNA, and are
present on chromosomes.
• Genes determine the Traits.
18

19. 19
Tissue Cell Nucleus Chromosomes DNA Genes

20. Chromosomes & Genes in Human
• Chromosomes come in homologous pairs, thus
genes also come in pairs.
Homologous pairs of chromosomes have matching
genes, which come one from female parent and one
from male parent
• Example: Humans have 46 chromosomes or 23 pairs.
One set from father – 23 in sperm
One set from mother – 23 in egg
20

21. One pair of Homologous Chromosomes
21
Homologous pair
of chromosomes
Gene for eye color
(blue eyes)
Gene for eye color
(brown eyes)

22. Alleles
Alleles are the group of two or more than two
different genes which determine the same
trait.
Example: blue eyes or brown eyes
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23. Dominant & Recessive Genes
23
• Gene that prevents the other gene from “showing” is
called dominant gene.
• Gene that does NOT “show” even though it is
present is called recessive gene
• Symbols of Dominant & Recessive genes:
• Dominant Gene: upper case letter “T”
• Recessive gene: lower case letter “t”

24. Example of Recessive & Dominant Genes
24
Straight thumb is dominant to hitchhiker thumb
T = straight thumb t = hitchhikers thumb
Always use the same letter for the same alleles.
(Not use S = straight, h = hitchhiker’s)
Straight thumb = TT
Straight thumb = Tt
Hitchhikers thumb = tt
Must have 2 recessive alleles for a recessive
trait to “show”

25. Homozygous & Heterozygous
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• When both genes of a pair are the same it is
called homozygous or purebred
TT – homozygous dominant
tt – homozygous recessive
• When both genes are Not same, one dominant
and one recessive gene, it is called
heterozygous or hybrid
Tt – heterozygous

26. BB =Black (Homozygous)
&
Bb = Black (Heterozygous)
(has dominant gene of Black and
recessive gene of white)
bb = White (Homozygous)
(Has both recessive genes of white)
26

27. Genotype & Phenotype
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• Combination of genes an organism has (actual gene
makeup) is called genotype
Example: TT, Tt, tt
• Physical appearance resulting from gene make-up is
called phenotype
Example: hitchhiker’s thumb or straight thumb

28. Punnett Square and Probability
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• Punnett Square is a two by two table method is
used to predict the possible gene makeup of
offspring.
• Example: Black fur (B) is dominant to white fur (b) in
mice. Cross a heterozygous male with a homozygous
recessive female.
Black fur (B)
White fur (b)
Heterozygous
male
White fur (b)
White fur (b)
Homozygous
recessive female

29. Bb Bb
bb bb
Possible offspring – 2N
Male gametes - N
(One gene in
sperm)
Female gametes – N
(One gene in egg)
Male = Bb X Female = bb
Genotypic ratio = 2 Bb : 2 bb
50% Bb : 50% bb
Phenotypic ratio = 2 black : 2 white
50% black : 50% white
b
b
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B
b
b

30. Sex Determination
30
• Human has 46 chromosomes or 23 pairs
• 22 pairs are homologous (look alike) and called autosomes, which
determine body traits
1 pair is the sex chromosomes, which determines sex (male or female)
• Females sex chromosomes are homologous (look alike), label XX
Males sex chromosomes are different, label XY

31. XX XX
XY XY
X
• What is the probability of a couple having a boy? Or a girl?
Chance of having female baby? 50%
male baby? 50%
Who determines the sex of the child? Male father
X
X
Y
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32. • When one allele is NOT completely dominant over another (they blend) –
incomplete dominance
Example: In flowers, the red (R) color is incompletely dominant over white
(W) color. The hybrid color is pink. Give the genotypic and phenotypic ratio
from a cross between 2 pink flowers.
RW X RW
RR RW
RW WW
W
R
W
Genotypic = 1 RR : 2 RW : 1 WW
Phenotypic = 1 red : 2 pink : 1 white
R
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Incomplete Dominance & Co-dominance

33. • When both alleles are expressed, are called Co-
dominance
Example: In certain chickens black feathers are
codominant with white feathers. Heterozygous
chickens have black and white speckled feathers.
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Co-dominance

34. • Genes for sex-linked traits
are located only on the X
chromosome (NOT on the Y
chromosome)
• X-linked alleles always show
up in males whether
dominant or recessive
because males have only
one X chromosome
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Sex-linked Traits

35. Examples of Recessive Sex-linked Disorders
Colorblindness
Is a disorder in which a person is unable to
distinguish between certain colors
35
You should see 58 (upper left), 18 (upper
right), E (lower left) and 17 (lower right).

36. Hemophilia:
Is a disorder in which blood won’t clot
36

37. Multiple Alleles
• 3 or more alleles of the same gene that code for a single trait
• In humans, blood type is determined by 3 alleles: A, B, and O
BUT each human can only inherit 2 alleles
Dominant: A and B (codominance)
Recessive: O
Blood type: A = AA or AO
B = BB or BO
AB = AB
O = OO
37

38. A B
Example: What would be the possible blood types of
children born to a female with type AB blood and
a male with type O blood?
AB X OO
AO BO
AO BO
O
O
Children would be type A or B only
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39. Euploidy & Aneuploidy
• Euploidy
– Normal variations of the number of complete sets
of chromosomes
– Haploid, Diploid, Triploid, Tetraploid, etc…
• Aneuploidy
– Variation in the number of particular
chromosomes within a set
– Monosomy, trisomy, polysomy
39

40. Gene Mutation
• Mutation is sudden genetic change (change in base pair
sequence of DNA)
• Mutation Can be:
• Harmful mutations: Organism less able to survive e.g
genetic disorders, cancer, death
• Beneficial mutations: Allows organism to better survive,
provides genetic variation
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• Neutral mutations: Neither
harmful nor helpful to
organism

41. Types of Mutation
Mutations can occur in 2 ways:
1. Chromosomal mutation
1. Gene/point mutation
41

42. Chromosomal mutation:
• less common than a gene mutation
• Has more drastic affects on entire chromosome,
so affects many genes rather than just one
• caused by failure of the homologous
chromosomes to separate normally during
meiosis
• chromosome pairs no longer look the same, too
few or too many genes, having different shape
42

43. Example of Chromosomal Mutation
43

44. Types of Chromosome Mutations
• May be Point/Gene Mutation or Chromosomal
mutation.
• Five types exist:
–Deletion
–Inversion
–Translocation
–Nondisjunction (Chromosomal)
–Duplication

45. Deletion
• Due to breakage, a piece of a
chromosome is lost

46. Inversion
• Chromosome segment breaks off
• Segment flips around backwards
• Segment reattaches

47. Duplication
• Occurs when a gene sequence is
repeated

48. Translocation
• Involves two chromosomes that aren’t
homologous
• Part of one chromosome is transferred
to another chromosomes

49. Translocation

50. Chromosomal Mutation
(Nondisjunction)
• Failure of chromosomes to separate
during meiosis
• Causes gamete to have too many or too
few chromosomes

53. 53

54. • Monosomy (Turner’s Syndrome)
• Trisomy (Down’s Syndrome & Klinefelters’s
syndrome)
• Polysomy
54

55. Down’s Syndrome
• Is a disorder in which there is an extra
chromosome at pair #21. Total number of
chromosome is 47 instead 46. Is referred as
Trisomy 21
55

56. Down’s Syndrome
56

57. Clinical Manifestations of Down’s Syndrome
• Upward slant to eyes (Mongolian Eyes).
• Small ears that fold over at the top.
• Small, flattened nose.
• Small mouth, making tongue appear large.
• Short neck.
• Small hands with short fingers.
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58. Down’s syndrome
58

59. Cont…
• Low muscle tone.
• Single deep crease across center of palm.
• Looseness of joints.
• Small skin folds at the inner corners of the eyes.
• Excessive space between first and second toe.
• In addition, down syndrome always involves
some degree of mental retardation, from mild to
severe. In most cases, the mental retardation is
mild to moderate.
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60. Turner’s Syndrome
• There are only 45 chromosomes, missing a sex
chromosome (X)
• Girls affected: short, slow growth, heart
problems
60

61. Clinical Manifestation of Turner’s Syndrome
• Turner syndrome is associated with
underdeveloped ovaries, short stature,
webbed, and is only in women.
• Bull neck, and broad chest. Individuals are
sterile, and lack expected secondary sexual
characteristics.
• Mental retardation typically not evident.
• Chromosomal or monogenic?
61

62. Turner’s Syndrome
62

63. Klinefelter’s Syndrome
• There are 47 chromosomes instead 46, there is
an extra X chromosomes (XXY)
• Boys affected: low testosterone levels,
underdeveloped muscles, sparse facial hair
63

64. Clinical Manifestation of Klinefelter’s Syndrome
• Disorder occurring due to nondisjunction of
the X chromosome.
• The Sperm containing both X and Y combines
with an egg containing the X, results in a male
child.
• The egg may contribute the extra X
chromosome.
64

65. Cont…
• Males with some development of breast
tissue normally seen in females.
• Little body hair is present, and such person are
typically tall, have small testes.
• Infertility results from absent sperm.
• Evidence of mental retardation may or may
not be present.
65

66. Kleinfilter’s syndrome
66

67. 67

68. Point to Note!!
• Having an extra set of chromosomes is fatal in
animals, but in plants it makes them larger
and hardier.
68

69. 69

70. • Most common and least drastic
• Only one gene is altered
70
Gene or Point Mutation

71. Recessive Gene Mutation
1. Sickle Cell Anemia
Red blood cells are sickle
shaped instead of round and
cannot carry enough oxygen
to the body tissues.
Heterozygous condition
protects people from malaria
71

72. 2. Cystic Fibrosis
• A heredity, recessive gene
disorder in which Mucous
builds up in the lungs &
pancreases that is difficult
to clear, which leads to
lung congestion and
infection. There is also
malabsorption of nutrition
by pancreas
72

73. 3. Tay-Sachs Disease
• Deterioration of the nervous
system leads to early death.
• Mutated genes produce enzymes
that are less effective than
normal at breaking down fatty
cell products known as
gangliosides.
• As a result, gangliosides build up
in the lysosomes and overload
cells.
• Their buildup ultimately causes
damage to nerve cells.
73

74. 4. Phenylketonuria (PKU)
• An amino acid
common in milk
cannot be broken
down and as it builds
up, and it causes
mental retardation.
• Newborns are tested
for this
74

75. Dominant Gene Mutations
• There are two types of disorders in which Dominant
gene is involved:
1. Huntington’s disease
– Gradual deterioration of brain tissue, shows up in middle
age, and is fatal
2. Dwarfism
– Short height with variety of skeletal abnormalities
75

76. Dwarfism
76

77. Detecting Genetic Disorders
• Picture of an individual’s chromosomes, called
karyotype
• Amniotic fluid surrounding the embryo is removed for
analysis. This process is called amniocentesis
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Female with Down’s syndrome

78. Thank You
The Great Class!
Any Question?
78