Download Genetics

1- human genome project 
2- DNA structure 
3- genetic disorders 
4- mendelian inheritance 
5- autosomal dominant inheritance

DNA consists of long chains of molecules 
called nucleotides. Each nucleotide consists of a
nitrogenous base(pyrimidine and purine ),
deoxyribose sugar and a phosphate group.
DNA structure is in the form of two
polynucleotide chains arranged in a double
helix.
The arrangement of the bases in the double 
helix is organised such that adenine always
pairs with thymine, and cytosine always pairs
with guanine. Thus the arrangement of
nucleotides in the two chains is
complementary. Thymine is not present in
RNA but is substituted by uracil.
The pyrimidines are cytosine (C) and thymine
(T); the purines are guanine (G) and adenin(A

DNA exists not as one long molecule, but as 
multiple fragments that together with a protein
skeleton (chromatin) form chromosomes
Every human cell has 23 pairs of chromosomes.
One copy of each chromosome is inherited
from each parent. Twenty-two pairs of
chromosomes are autosomes; the remaining
pair is called the sex chromosomes. Females
have two X chromosomes; males have one X
and one Y.

DNA is packaged into chromosomes and at a
very simple level these can be considered as
being made up of tightly coiled long chains of
genes. Unlike DNA, chromosomes can be
visualized during cell division using a light
microscope, under which they appear as
thread-like structures or 'colored bodies'. The
word chromosome is derived from the Greek
chroma (= color) and soma (= body).

Under the electron microscope chromosomes
can be seen to have a rounded and rather
irregular morphology

common, with 2% of live-born babies having a
significant congenital malformation and about
5% a genetic disorder
burdensome to the affected individual, family
and society, as many are associated with severe
and permanent disability
1. Single gene mutations,((Mendelian disorders)
2. Chromosomal disorders
3. Multifactorially inherited conditions
4. Disorders that show an unusual pattern of
inheritance
5. Teratogenically caused conditions
Disorders with these patterns of inheritance,
described by Mendel in 1865, are rare
individually, but collectively numerous, with
over 15 000 single gene traits or disorders
described
There are three classic forms of genetic 
inheritance: autosomal dominant, autosomal
recessive, and X-linked

This is the most common mode of Mendelian
inheritance
Autosomal dominant inheritance is determined
by the presence of one abnormal gene on one
of the autosomes (chromosomes 1–22).
Male and female offspring each have a 1 in 2
(50%) chance of inheriting the abnormal gene
from an affected parent
Tuberous sclerosis
•
Marfan syndrome
•
Neurofibromatosis
•
Huntington's disease
•
Retinoblastoma
•
Waardenburg syndrome
•
Myotonic dystrophy
•
Familial hypercholestrolemia (LDL receptor defect Type IIa)
Adult polycystic kidney disease
•
von Hippel Lindau
•
Familial adenomatous polyposis and Peutz Jeghers Syndrome
Hereditory spherocytosis
•
Achondroplasia
•
Ehlor's Danlos (vascular type)
•
Acute intermittent porphyria
•
Hypertrophic Obstructive Cardiomyopathy (HOCM)
•
Von Willebrand Disease
•
Polydactyly
•
Osteogenesis Imperfecta (Except Type VII)
•
Hereditary hemorrhagic telengiactasia (Osler-weber-rendu
syndrome)
Osteopetrosis Type II (Adult type)
•
Hypokalemic Periodic Paralysis
•
•
•
•
Within a family, some affected individuals may
manifest the disorder mildly and others more
severely. For example, a parent with tuberous
sclerosis may have mild skin abnormalities
only, but his or her affected child may have, in
addition, epilepsy and learning difficulties.

Refers to the lack of clinical signs and symptoms
in an individual who must have inherited the
abnormal gene. An example of this is
otosclerosis, in which only about 40% of gene
carriers develop deafness
A new mutation in one of the gametes leading 
to the conception of the affected person. This is
the most common reason for absence of a
family history in dominant disorders, e.g. >80%
of individuals with achondroplasia have
normal parents.
Trait appears in every generation
Each child of an affected parent has a 1 in 2
chance of being affected
Males and females are equally affected
Male-to-male transmission occurs
Achondroplasia
achondroplasia is the most common skeletal
dysplasia in humans. The bony abnormalities
in achondroplasia lead to short stature,
macrocephaly, a flat midface with a prominent
forehead, and rhizomelic shortening of the
limbs.
Clinical symptoms mostly involve three 
systems: cardiac, musculoskeletal, and
ophthalmologic. Musculoskeletal findings
include dolichostenomelia (a tall, thin body
habitus), arachnodactyly (spider-like fingers
and toes), abnormalities of the sternum
(pectus excavatum or carinatum),
kyphoscoliosis, pes planus, and joint laxity
Eye findings include high myopia, which 
eventually can lead to vitreoretinal
degeneration; an abnormal suspensory
ligament of the lens, which can lead to ectopia
lentis (dislocation of the lens; in Marfan
syndrome, the lens usually dislocates upward
and outward); and cataracts. Cardiac findings
include a weakened aortic wall, which leads to
progressive dilation of the aortic root. Aortic
insufficiency followed ultimately by aortic
dissection is a common complication of this
disorder