Medical Genetics and Its Basic Principles
Many diseases develop as a result of interaction between the genetic and environmental factors.
Some diseases are predominantly genetic, e.
g, achondrophasia and Turner's syndrome, other cases are predominantly environmental, e.
g Typhoid fever and Tuberculosis, while in many other genetic and environmental factors, play similar roles, e.
g, diabetes, hypertension.
Genetic disorders may be classified into: 1.
Single gene disorders 2.
Chromosomal disorders and 3.
Polygenic disorders.
Single gene disorders are those involving a mutation or change in a single gene.
For example Achondroplasia, thalassaemic, sickle cell disease, haemophilia, etc.
Chromosomal disorders are those in which a change or alteration of the chromosomal number or structure can be demonstrated e.
g, Down's syndrome, Klinefelter's syndrome or Turner's syndrome.
Polygenic disorders are those which arise from the combined influence of multiple small genetic defects.
Basic principles of Genetics Genetic information is contained in deoxyribonucleic acid (DNA).
It has a double stranded structure, twisted in the form of a helix, and distributed along the chromosomes.
The strand consists of deoxyribose residues linked by phosphate (covalent phosphate diester) bonds.
Each strand is connected with one of four bases; adenine, thymine, cytosine or guanine.
The bases on the opposite sides in the two strands are aligned together as a base pair by hydrogen bonds.
Adenine always pairs with thymine, and cytosine with guanine.
The role is to contain and transmit genetic information.
That information is encoded by the sequence of the bases.
DNA transmits this genetic information by unravelling its two strands and exposing previously paired bases, thus forming a nucleic acid.
If the information is to be propagated to daughter cells, the new strands of nucleic acid synthesized is more DNA.
This process of propagation is called replication.
If the information is to be used by the cell, the new strand is ribonucleic acid (RNA).
This process is called transcription.
RNA differs from DNA in having ribose as its sugar, and the base Uracil instead of thymine.
Uracil, like thymine, forms base pair with adenine.
The "transcribed" RNA acts as a messenger RNA, which travels from the chromosome on which it is synthesized to the cytoplasmic ribosomes, where it directs the assembly of aminoacids into proteins.
This process is called translation.
The aminoacids are carried to the ribosomes by small RNA molecules called transfer RNAs (tRNAs).
Each of the 20 aminoacids has one or more specific tRNAs.
Gene is that length of DNA which acts as a functional unit.
It is also termed as cistron.
One gene produces one polypeptide, which may combine with other polypeptides produced by other genes to form biologically active proteins like hormones or enzymes.
Some diseases are predominantly genetic, e.
g, achondrophasia and Turner's syndrome, other cases are predominantly environmental, e.
g Typhoid fever and Tuberculosis, while in many other genetic and environmental factors, play similar roles, e.
g, diabetes, hypertension.
Genetic disorders may be classified into: 1.
Single gene disorders 2.
Chromosomal disorders and 3.
Polygenic disorders.
Single gene disorders are those involving a mutation or change in a single gene.
For example Achondroplasia, thalassaemic, sickle cell disease, haemophilia, etc.
Chromosomal disorders are those in which a change or alteration of the chromosomal number or structure can be demonstrated e.
g, Down's syndrome, Klinefelter's syndrome or Turner's syndrome.
Polygenic disorders are those which arise from the combined influence of multiple small genetic defects.
Basic principles of Genetics Genetic information is contained in deoxyribonucleic acid (DNA).
It has a double stranded structure, twisted in the form of a helix, and distributed along the chromosomes.
The strand consists of deoxyribose residues linked by phosphate (covalent phosphate diester) bonds.
Each strand is connected with one of four bases; adenine, thymine, cytosine or guanine.
The bases on the opposite sides in the two strands are aligned together as a base pair by hydrogen bonds.
Adenine always pairs with thymine, and cytosine with guanine.
The role is to contain and transmit genetic information.
That information is encoded by the sequence of the bases.
DNA transmits this genetic information by unravelling its two strands and exposing previously paired bases, thus forming a nucleic acid.
If the information is to be propagated to daughter cells, the new strands of nucleic acid synthesized is more DNA.
This process of propagation is called replication.
If the information is to be used by the cell, the new strand is ribonucleic acid (RNA).
This process is called transcription.
RNA differs from DNA in having ribose as its sugar, and the base Uracil instead of thymine.
Uracil, like thymine, forms base pair with adenine.
The "transcribed" RNA acts as a messenger RNA, which travels from the chromosome on which it is synthesized to the cytoplasmic ribosomes, where it directs the assembly of aminoacids into proteins.
This process is called translation.
The aminoacids are carried to the ribosomes by small RNA molecules called transfer RNAs (tRNAs).
Each of the 20 aminoacids has one or more specific tRNAs.
Gene is that length of DNA which acts as a functional unit.
It is also termed as cistron.
One gene produces one polypeptide, which may combine with other polypeptides produced by other genes to form biologically active proteins like hormones or enzymes.
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