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Genetics
Islamic University
College of Nursing
Introduction

Our understanding of human genetics improved in the few
past years.

This was occurred after the discovery of the gene map.

Human diseases and the different disorders are influenced by
both environmental and genetic factors with varying
degrees, for example, Down syndrome is pure genetic
disease, Scurvy is pure due to environmental factors. In
between combined such as DM, HTN (Multi-factorial).
Human Cell

Normal human cell contains 46 (23 pairs)
chromosomes, 22 pair autosomes and the 23rd
chromosome is sex pair.

XX for the female and XY for the male.

Approximately 50,000 genes encoded in the
human DNA. (Deoxyriboneuclic Acid)
Mitosis
46
Cell Division
23
23
Meiosis I
46
23
23
23
23
23
Meiosis II
23
23
23
23
23
23
23
Spermatogenesis & Oogenesis

Gametogenesis in male and female are principally
the same but differ in timing of the various stages.

Spermatogenesis begin in the seminefrous tubules
around the puberty & continue out life.

Oogenesis begin in the intrauterine life but is
arrested in meiosis I, with completion of the cycle
when ovulation occurs and continue up to 50 years
old.
Sexual Division of Ova and sperm
23
Ova
46
Normal
Polar body
Abnormal
Meiosis I
23
Normal
23
Sperm
46
23
Meiosis II
Not contain cytoplasm
Not contain cytoplasm
Polar body
Abnormal
Duplication of genetic materials
Female Chromosomes
Male chromosomes
The Same
Short arm (P)
Proteins
A
B
C
D
E
F
A
B
C
D
E
F
Centromere
Long arm (q)
Preparation for genetic study
1- Separation of WBCs by centrifugation.
2- Cultivate the lymphocytes by adding
phytohemagglutinin.
3- Arrest cell division after about 70 hours by
adding colchicines to the culture.
4- Release the chromosomes from the nucleus by
adding hypotonic saline.
5- Fix and stain.
Indications for chromosomal studies
1.
Mental retardation.
2.
Multiple congenital abnormalities.
3.
Recurrent abortion.
4.
Infertility.
5.
Ambiguous sex.
6.
Leukemia.
7.
Failure to thrive child.
8.
Some syndromes. (turner).
Definitions:

Gene: describe the hereditary factor that
determine the trait or disorder.

Locus: is the position at which the structural
gene lies. Individuals have 2 alleles at each
locus.

Homozygous: if the 2 alleles at a single
locus are identical. (Recessive)
Definitions

cont…
Heterozygous: if the 2 alleles in a single
locus are different. (Dominant)

Dominant: if the condition is manifest with
single gene, example heterozygous state.

Recessive: if the condition is seen only in the
homozygous state. Occurred when the two
alleles are abnormal.
Autosomal Recessive

Recessive: the condition is seen only in the
homozygous state. (identical)

Occurred when the two alleles are abnormal.

The disorder is more common among
consangeous marriage. Siblings have one half of
their genes in common, where first cousins have
one-eight of their genes in common.

One third of inherited traits are AR.
Criteria of AR disorders
1.
Parents are usually healthy.
2.
Affected individuals are almost the offspring of
heterozygot carrier parents.
3.
Percent % to be affected of children if the parents are
carriers is 1:4.
4.
If both parents are affected all children will be
affected.
5.
Both sexes are affected equally.
6.
It causes mainly enzyme deficiency.
7.
Example: Cystic Fibrosis, Galactosomia,
Phenlketonurea, Thalassemia, and others.
Autosomal Dominant (AD)

Dominant means that the disease allele or gene
need to be present only in single copy
(heterozygot) to result in phenotype.

The affected individuals posses both the
abnormal and normal gene.

More than half of the inherited traits are
autosomal dominant.
Criteria of Autosomal (AD) disorder

Disease is transmitted from generation to
generation and can be tracked to several
generations.

Sporadic cases can occur due to new mutations,
it occur more frequently in sever cases in which
the chance of survival or reproduction of the
affected persons are low.

It affect both sexes equally.
Criteria of Autosomal (AD) disorder

The risk of transmission to the offspring is 50%
they show variability in severity.

Anticipation: The severity of the disease
tended to increase with each generation.

An example: Myotonic dystrophy, the
grandfather could have cataract only, the
mother had myotonia and muscle weakness and
the affected child had congenital myotonic
dystrophy with developmental delay.
Example of AD

Achondroplasia. (disease of bone growth cause short
structure M. 131, F124, not able to convert cartilage into
long bone).

Neurofibromatosis.
(NF1)causes skin changes and
deformed bones. It usually starts in childhood. Sometimes
the symptoms are present at birth. (NF2) causes hearing
loss, ringing in the ears, and poor balance. Symptoms often
start in the teen years.
Example of AD

Polycystic Kidney disease.
(ADPKD) is a multi-systemic and
progressive disorder characterized by cyst formation and enlargement in
the kidney and other organs (eg, liver, pancreas, spleen). Up to 50% of
patients with ADPKD require renal replacement therapy by 60 years of age.

Retinoblastoma.
(is the most common primary ocular
malignancy of childhood).

Spherocytosis.
is a familial hemolytic disorder with marked
heterogeneity of clinical features, ranging from an asymptomatic condition
to fulminant hemolytic anemia
X-linked diseases






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Transmitted by heterozygous mother to sons
Daughters - 50% carriers, 50% healthy
Sons - 50% diseased, 50% healthy
Children of diseased father - sons are healthy,
all daughters are carriers
Hemophilia A (defect of Factor VIII)
Hemophilia B (defect of Factor IX)
Muscle dystrophy (Duchen disease)
Autosomal disorders
Trisomy 21 (Down syndrome)

Most frequent - 1:700 births; parents have normal
karyo-type.

Maternal age has a strong influence: <20 y.
1:1550 live births, >45 y. 1:25 live births

Most frequently is abnormality in ovum (ovum is
under long-time influence of environment)


HEREDITY The passing of traits from parent to offspring.
ALLELE The different forms of a trait that a gene may
have. One form of a gene

GENOTYPE
An organism's genetic makeup.

PHENOTYPE
Outward physical appearance and behavior of an organism.

TRAIT Ways of looking, thinking, or being. Traits that are
genetic are passed down through the genes from parents
to offspring.
Autosomal Dominant
Autosomal Recessive
Autosomal Recessive
Sex linked disease