- Human DNA and RNA.

Human DNA

All nucleic acids are polynucleotides. A nucleotide consists of three components:

1.     A nitrogenous base: (Adenosine and guanine which are based on purine rings, Thymine and cytosine which are based on pyrimidine rings).

2.     A pentose sugar (deoxyribose in DNA and Ribose in RNA) at 3′ end

3.     1-3 phosphate groups at 5′ end

 There are two kinds of nucleic acids:

o   Deoxyribonucleic acid (DNA)

o   Ribonucleic acid (RNA).

•Two polynucleotide chains are linear but antiparallel (i.e. one chain runs in a 5' to 3' direction; the other runs 3' to 5').

•   The sugar and phosphate groups form the linear backbone of the strands with the bases projecting inwards towards their partners held together by hydrogen bonds between the opposing bases:

ü  Adenine (A) pairs only with thymidine (T) (2 hydrogen bonds)

ü  Guanine (G) pairs only with cytosine (C) (3 hydrogen bonds).

· Multiple fragments that, together with a protein skeleton (chromatin), form chromosomes.

· Site: Nucleus and Mitochondria.

- Indications of genetic testing!

Medical applications (indications of genetic testing, karyotyping, chromosomal culture, analysis) :

1.     Multiple congenital anomalies:

Birth defects > one developmental regions of the body

A.    Confirmation of a clinical diagnosis

B.    Estimate recurrence risk of future sibling

2.     Dysmorphic features or well-defined syndrome e.g down syndrome

3.     Unexplained Mental retardation (chromosomal abnormalities are responsible for 1/3  50% of MR which is due to genetic factor)   

4.     Pubertal failure

5.     Ambiguous genitalia

Provide diagnosis e.g turner, klinfilter

If Normal karyotyping → other endocrinal disorders

6.     Infertility: at least 5% of infertile men are killfilter.

7.     Recurrent spontaneous Abortions and miscarriage: