Fundamentals of Genetics, DNA and Biotechnology

Posted on Jan 7, 2026 in Biology

Genotype and Phenotype

Genotype: genetic constitution of an individual character or referring to a whole set of genes (e.g., AA, Aa).

Phenotype: external expression of the genotype. The phenotype is the property that presents in the individual (e.g., yellow, green).

Alleles: each of the variants of a gene. For each gene, the individual has a pair of alleles, which are commonly represented with a letter: A (dominant), a (recessive).

Heterozygous: an individual who carries two different alleles (e.g., Aa).

Mendelian Model and Laws

Mendelian model: Nowadays, each genetic trait is considered to be determined by a pair of factors (genes) that are passed to offspring according to these laws:

  1. First law — Principle of uniformity: the first filial generation (F1), resulting from crossing two inbred lines, is uniform; that is, it shows the character of one of the parents.
  2. Second law — Principle of segregation: a trait that is not expressed in the first generation can reappear in the second generation because the factors segregate (separate) in the gametes and recombine in the offspring.
  3. Third law — Principle of independent assortment: factors for different characters follow the above rules independently, without one influencing the proportions obtained for the other.

DNA and Nucleic Acids

DNA: stands for “deoxyribonucleic acid.” DNA is composed of:

  • A nitrogenous base: there are five common nitrogenous bases: adenine, cytosine, guanine, thymine, and uracil (uracil replaces thymine in RNA).
  • A pentose: either ribose or deoxyribose.
  • A phosphate group.

There are two types of nucleic acids:

  • Ribonucleic acid (RNA): RNA nucleotides contain ribose, phosphate, and one of these nitrogenous bases: adenine, cytosine, guanine, or uracil. There are several subtypes of RNA, such as mRNA and tRNA.
  • Deoxyribonucleic acid (DNA): DNA nucleotides are composed of deoxyribose, phosphate, and one of four bases: adenine, cytosine, guanine, or thymine.

Amino Acids and Proteins

Amino acids: there are 20 different amino acids that become part of the long chains of proteins. These molecules are central to vital activity. Very important proteins are enzymes, which enable the chemical reactions that occur in cells.

Transgenic Organisms and Gene Therapy

Transgenic organisms: organisms developed from a cell into which a DNA fragment from another living being has been introduced.

Gene therapy: treatment of a disease based on the introduction of genes into the body.

RNA and Protein Synthesis

RNA: RNA types include mRNA, rRNA, and tRNA.

Protein synthesis:

  1. Transcription: during this stage, the information stored in DNA is transferred to a type of RNA called messenger RNA (mRNA). The mRNA consists of a complementary base sequence based on a fragment of the DNA strand that served as its template. In RNA, adenine pairs with uracil instead of thymine.
  2. Translation: formation of a chain of amino acids according to the nucleotide sequence of mRNA. After transcription, the mRNA enters the cytoplasm and binds to ribosomes. Amino acids are attached to transfer RNA (tRNA), which is responsible for transporting each amino acid to the ribosome where the mRNA is read; the amino acids then join, allowing the formation of the protein chain.

Recombinant Organisms and Assisted Reproduction

Recombinant organisms: we speak of recombinant organisms when referring to genetically engineered viruses or bacteria.

Assisted reproduction procedures:

  1. Artificial insemination: introduction of semen into the uterus through a cannula. Semen can be obtained from the male partner or, if not possible due to infertility, from an anonymous donor via a sperm bank.
  2. In vitro fertilization: fertilization achieved in the laboratory and then implantation of the embryo in the mother’s uterus. The procedure involves implantation of the embryo in the uterine wall. Usually 2 to 3 embryos are implanted; the others are kept frozen to allow further attempts if the first is not successful. If semen quality is low, one can resort to the technique of intracytoplasmic sperm injection.

Applications of the Human Genome Project

Applications of the Human Genome Project:

  1. Genetic testing: for different types of cancer, diabetes, and other conditions. These tests may reveal the probability of developing these diseases and therefore allow preventive measures.
  2. Pre-transplantation genetic diagnosis: a healthy baby could save the life of a sick child (for example, a sibling) thanks to a transplant.
  3. Knowledge about human evolution: understanding migration of populations throughout history.

Gene therapy: is the treatment of a disease based on the introduction of genes into the body.