Chromosome Alterations and Genetic Engineering Techniques
Chromosomal Alterations
Structural Alterations
These affect the structure of chromosomes, impacting gene location. They are usually caused by errors in mitosis and meiosis, mainly affecting homologous chromosome pairing during prophase I. There are four types:
- Deficiencies or Deletions: Loss of a chromosome segment, affecting multiple genes. Example: Cri du chat syndrome.
- Duplications: Repetition of a chromosome segment, often in heterozygous series. Cytologically recognized during mating as a duplicated area.
- Inversions: A chromosomal segment rotates 180ยบ, changing gene order but not location. Detected by inversion ties.
- Translocations: Change of location of a chromosomal segment. It may not affect the individual but can seriously affect offspring through abnormal gametes.
Numerical Alterations (Genomic)
These are not observable by microscope but affect chromosome number due to errors in mitosis and meiosis, often caused by poor chromosome distribution or inducing substances. There are two types:
- Euploidias: Affect a complete haploid set; haploidy is the reduction of the normal chromosome number.
- Aneuploidy: Affecting one or a few chromosomes due to poor separation of homologues during meiosis. Examples include:
- Trisomy 21 (Down syndrome): Causes mental retardation and physical changes.
- Klinefelter syndrome: Males with feminization, reduced testes, azoospermia, sterility, and mental retardation.
- Trisomy X: Females with potential mental retardation.
- Turner syndrome: Females with underdeveloped characteristics, sterile ovaries, and lack of menstruation.
- XYY syndrome: Males showing very aggressive behavior.
Genetic Engineering
A set of techniques to intentionally alter the genetic material of a cell or individual.
Procedures
- Recombinant DNA Technology: Combines DNA pieces not naturally found together.
- Genetic Cloning: Isolation and replication of a gene of interest. Steps:
- Isolation of genes by DNA fragments using restriction enzymes.
- Joining DNA fragments to a cloning vector using DNA-ligase, forming recombinant DNA.
- Introducing the recombinant DNA molecule into a host organism for replication (cloning).
- Detecting the cloned gene and producing cells carrying that gene.
Restriction Enzymes
Bacterial enzymes that cut DNA at specific points, creating manageable fragments.
Cloning Vectors
Small DNA molecules used for recombining and replicating genes, facilitating DNA fragment transport to cells. Examples:
- Plasmids: Small, circular DNA molecules in bacteria, independent of the bacterial chromosome.
- Bacteriophages: Can transfer DNA fragments to bacteria via transduction. Used when the DNA fragment is larger than what plasmids can handle.
Host Cells
Cells, usually bacteria, into which vectors are introduced for replication. Common hosts include Escherichia coli, Bacillus subtilis, and Saccharomyces cerevisiae (yeast).
Applications of Genetic Engineering
Medicine
- Production of Therapeutic Substances (proteins):
- Hormones:
- Somatostatin: Inhibits growth hormone (GH) synthesis.
- Insulin: Regulates blood glucose concentration. Achieved by cloning the human gene in bacteria.
- Growth Hormone: Treats pituitary dwarfism.
- Enzymes:
- Interferons: Polypeptides produced in response to viral infections.
- Factor VIII: Blood coagulation factor, biotechnologically produced for hemophilia treatment.
- Renin: Enzyme for cheese making and certain drugs.
- Cellulase: Enzyme for cellulose hydrolysis, potentially vital for reducing world hunger.
- Recombinant Vaccines: Mainly viral, safer due to killed or attenuated pathogens, reproducible in high doses.
- Monoclonal Antibodies.
- Hormones:
- Diagnosis of Hereditary Diseases: Prenatal diagnosis of hemophilia, sickle cell anemia, muscular dystrophy, and Huntington’s chorea using Restriction Fragment Length Polymorphism (RFLP) technique.
- Gene Therapy: Inserting a normal gene (transgene) to replace a malfunctioning gene. DNA transmission can be done in two ways.