CYTO: PRELIMS

• Cytogenetics is a branch of genetics that deals with the study of inheritance in relation to the structure and function of chromosomes
• Genetics encompasses levels from DNA to genes to chromosomes and even the human genome
• In cytogenetics, topics include nucleic acids, chromosomes, genes, cell cycle, Mendelian patterns of inheritance, chromosomal abnormalities, and cytogenetic techniques like karyotyping and PCR
• Characteristics in genetics:

  • Character: a heritable feature that varies among individuals
  • Trait: each variant for a character
  • True Breeding: parents produce offspring with the same phenotype
  • Hybridization: mating or crossing of two varieties
  • Genotype: genetic composition of an organism
  • Phenotype: the visible expression of information contained in a gene
  • Locus: specific position on a chromosome where a gene is located
• A genetic map of Drosophila melanogaster shows the locations of different genes along the chromosome, like brown eyes affecting eye color near one end of chromosome 2
• Allele is an alternative form of a gene, Mendel proposed that each trait requires two related but different determinants
• Homozygous organisms have a pair of identical alleles at a given locus, while heterozygous organisms have two different alleles at a given locus
• Genes are nucleotide sequences coding for polypeptides, enzymes, or structural proteins
• Overview of the history of genetics and cytogenetics:

  • Before 1860: observations on gametes and cell structures
  • 1860-1900: Mendelian traits, chromosomes, and meiosis
  • 1900-1944: chromosomal theory, sex linkage, and genetic mutations
  • 1944-present: DNA, RNA, molecular genetics, gene cloning, and genome sequencing
• After the RNA primer is made, DNA polymerase III starts to synthesize the leading strand, elongating continuously in the 5' to 3' direction as the replication fork progresses

  
• The 3' end of a primer strand annealed to a template strand is being extended by the addition of a nucleotide by DNA polymerase, forming a phosphodiester bond and releasing pyrophosphate

  
• The replication fork is the point at which DNA is being replicated, with the replication machinery and point of attachment of DNA

  
• The leading strand is synthesized continuously in the 5' to 3' direction, while the lagging strand is synthesized discontinuously in the 3' to 5' direction

  
• DNA replication involves the unzipping of the double helix, resulting in two double helices like the original, with DNA polymerase performing the replication
• Mutations during DNA replication can result from errors in base pairing or DNA damage not repaired before the next replication cycle
• Groups of three nucleotide bases form a codon specifying one of the 20 amino acids used in protein sequences
• Transcription involves the conversion of DNA to RNA by RNA polymerase, with RNA differing from DNA in sugar, base, and being single-stranded
• Types of RNA include messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA), each playing a role in protein synthesis
• Recombinant technology began with the discovery of restriction endonucleases, allowing DNA from different sources to be joined, with applications in agriculture, industry, and medicine
• Genetic engineering involves cloning animals by transplanting a nucleus from a somatic cell into an enucleated egg cell to produce a genetically identical individual
• Genomics studies an organism's complete DNA or RNA sequence, gene organization, and expression, with potential for designing drug therapies for specific diseases
• Transcriptomics studies all transcribed genes and their expression changes in response to stimuli or diseases, offering tailored drug therapies for specific diseases
• Evolutionary genetics studies mechanisms leading to changes in allele frequencies in populations over time, with Charles Darwin describing evolution as a result of natural selection
• The Hardy-Weinberg equilibrium is used as a baseline for comparing populations to see if evolutionary processes are occurring, with the equation relating allele and genotype frequencies
• Sociobiology suggests that social behavior is under genetic control and is acted on by natural selection, similar to morphological or physiological traits
• Classical genetics concerns genes, mutations, and phenotypes, including the arrangement of genes on chromosomes, mutation generation methods, and inheritance patterns
• Pedigree analysis involves pictorial representation of related individuals and their exhibited phenotypes to determine inheritance patterns and gene locations
• Karyotyping represents all chromosomes in an individual, revealing sex and autosomal abnormalities or rearrangements
• The chromosomal theory of inheritance states that chromosomes, containing genes, are carriers of genetic material
• George Beadle and Edward Tatum suggested that one gene encodes one enzyme, with many enzymes made up of more than one polypeptide
• Gregor Mendel published basic rules of inheritance in 1866, predicting traits controlled by genetic elements and the diploid state of organisms
• The law of segregation states that alleles separate randomly during gamete formation, while the law of independent assortment describes how alleles of different genes sort independently into gametes
• Crosses were made to determine genetic control of mutant traits, leading to chromosomal mapping and the chromosomal theory of inheritance
• The DNA sequence of a gene encodes the amino acid sequence of a protein, with each strand of linear DNA containing 3' and 5' ends with specific groups
• The ability to locate the relative positions of genes on chromosomes by crossing individuals with different phenotypes led to chromosomal mapping and the chromosomal theory of inheritance
• The 3' end of a primer strand annealed to a template strand is extended by the addition of a nucleotide by DNA polymerase, forming a phosphodiester bond and releasing pyrophosphate

  
• The replication fork is the point at which DNA is being replicated, with the replication machinery carrying out the process and the point of attachment of DNA to the machinery

  
• DNA replication involves the leading strand synthesized continuously in the 5' to 3' direction and the lagging strand synthesized discontinuously in the 3' to 5' direction

  
• DNA replication is a fundamental process where DNA is synthesized to form another DNA, minimizing mistakes and ensuring damage is repaired to prevent it from being transferred to the next generation
• Watson and Crick proposed the structure of DNA and suggested a self-duplication mechanism based on the complementary nature of DNA strands, predicting a semiconservative nature of replication