Fundamentals of Genetics: DNA, Genes, and Human Biology

DNA Structure and Genetic Information

Genes are the carriers of biological information, found inside every cell. Their precise location was not known until their discovery within chromosomes. The chromosome number in sex cells is half that which exists in other somatic cells. Genes are contained within chromosomes, and each gene is made up of the molecule known as DNA (Deoxyribonucleic Acid).

DNA Replication: Ensuring Genetic Continuity

Each time a cell divides into two, the two resulting cells must receive the same genetic material. For this to happen, it is essential that DNA copies itself, a process known as replication or duplication.

RNA: Types and Functions

RNA (Ribonucleic Acid) is typically single-stranded. In RNA, the sugar deoxyribose is replaced by ribose, and the nitrogenous base thymine is replaced by uracil. There are several types of RNA, each with specific functions:

• Messenger RNA (mRNA): Carries a copy of the genetic message from DNA to the ribosomes.
• Ribosomal RNA (rRNA): A component of ribosomes, it binds amino acids to form protein chains.
• Transfer RNA (tRNA): Carries specific amino acids to the ribosome during protein synthesis.

Protein Synthesis: The Translation Process

The process of translation converts the genetic message carried by mRNA into a protein. This involves several steps:

1. The genetic message, copied into mRNA during transcription, is identical to the single-stranded DNA template.
2. The mRNA molecule is small enough to leave the nucleus and travel to the cytoplasm, unlike DNA.
3. Ribosomes, the cellular machinery for protein synthesis, bind to the mRNA.
4. Transfer RNA (tRNA) molecules, each carrying a specific amino acid, bind to complementary codons on the mRNA within the ribosome.
5. Amino acids are linked together in the sequence specified by the mRNA, forming a polypeptide chain.
6. The mRNA exists as a separate and distinct fragment from DNA, containing only the necessary information for a particular protein.

The Human Genome Project and Its Goals

The human genome refers to the complete set of genes in a human organism. Key objectives related to understanding the human genome include:

• Completing the sequence of all nucleobases in human DNA.
• Locating and mapping all genes on every chromosome.
• Understanding the complex relationships between genes.
• Discovering and identifying novel or unknown genes.

Biotechnology: Applications and Impact

Biotechnology is a field of biology that uses living organisms and biological systems to develop products and technologies to benefit humanity.

Current Advancements in Biotechnology

Modern biotechnology is largely based on the achievements of genetic engineering. Its ongoing development is expected to cause significant changes in various aspects of our lives, from medicine to agriculture.

Karyotype: Chromosomal Analysis

A karyotype reflects the number and characteristic structure of chromosomes of a species. It is used to compare an individual's chromosomes, often to detect abnormalities.

Karyogram: Visualizing Chromosomes

A karyogram is a graphical representation of a karyotype, where chromosomes are ordered by homologous pairs according to size and banding patterns.

Human Blood Groups: ABO System

Blood groups are a well-known example of discontinuous characteristics, determined by specific antigens present on the membrane of red blood cells. These antigens can react when they come into contact with blood from another individual. The ABO system classifies blood into four main types:

• Type A: Has antigen A on red blood cells and produces anti-B antibodies in the plasma.
• Type B: Has antigen B on red blood cells and produces anti-A antibodies in the plasma.
• Type AB: Has both antigen A and antigen B on red blood cells and produces neither anti-A nor anti-B antibodies in the plasma.
• Type O: Has neither antigen A nor antigen B on red blood cells but produces both anti-A and anti-B antibodies in the plasma.

Genetic Alterations and Disorders

Genetic alterations can lead to various disorders. Here are some examples:

• Polydactyly: An alteration where an allele controls the number of fingers or toes, often resulting in more than the usual five digits.
• Albinism: Characterized by the absence of melanin, the substance responsible for pigmentation of the skin, eyes, and hair.
• Hemophilia: A genetic disorder involving the absence or deficiency of one of the factors required for blood coagulation. Even a small rupture of a blood vessel can lead to serious bleeding in affected individuals. Women can be carriers of the gene without exhibiting the disease themselves.
• Trisomy: A chromosomal alteration characterized by the presence of an extra copy of a chromosome (e.g., Trisomy 21, also known as Down syndrome).