Fundamentals of Genetics

1. DNA Replication

• Timing: S phase of interphase in the cell cycle.
• Context: Occurs before cell division.
• Mechanism: DNA is unwound into two single strands, each acting as a template for the synthesis of a new complementary strand. This process adheres to the principles of base pairing and semi-conservative replication.
• Enzymes Involved: DNA polymerase, DNA ligase, helicase, primase.

2. Transcription

• Location: Nucleus of the cell.
• Mechanism: RNA polymerase uses one strand of DNA as a template to synthesize an RNA molecule.
• Outcome: Produces an RNA molecule carrying genetic information from DNA to the ribosome.

3. Translation

• Location: Ribosomes.
• Mechanism: Ribosomes move along the RNA molecule, reading the genetic code and linking amino acids in a specific sequence.
• Outcome: Forms a polypeptide chain (protein).

4. DNA

• Distribution:
  • Eukaryotic cells: Nucleus, organelles (chloroplasts, mitochondria).
  • Prokaryotic cells: Nucleoid (no nuclear membrane).
• Structure: DNA is a double helix, consisting of two polynucleotide strands linked by hydrogen bonds between complementary nitrogenous bases (A-T, G-C).
• Function: Carries genetic information, controls protein biosynthesis.

5. Eukaryotes

• Includes: Protists, fungi, animals, and plants.
• Characteristics: Have a nucleus, organelles enclosed by cell membranes, more complex genomes than prokaryotes.

6. Prokaryotes

• Includes: Bacteria.
• Characteristics: Lack a nucleus, simpler genomes than eukaryotes, often have additional plasmid DNA.

7. Amino Acids

• Number: 20 types of amino acids.
• Function: The building blocks of proteins, involved in the structure and function of various proteins.

8. Genetic Recombination

• Occurrence: Prophase I of meiosis.
• Mechanism: Crossing over of homologous chromosome segments between pairs of homologous chromosomes.
• Outcome: Generates gametes with new combinations of genes.

9. Lactose in Gene Regulation

• Role: Lactose is an inducer in gene regulation in bacteria.
• Mechanism: Lactose binds to the repressor protein, causing the repressor protein to change conformation and become unable to bind to the operator region of the gene, allowing RNA polymerase to transcribe the gene.

10. Gene Regulation in Prokaryotes and Eukaryotes

• Prokaryotes: Primarily occurs at the level of transcription (regulating the transcription process).
• Eukaryotes: Occurs at both the transcriptional and post-transcriptional levels (regulating transcription, RNA processing, translation, or post-translation).

11. Levels of DNA Coiling

• Nucleosome: 11 Angstroms.
• Chromatin fiber: 30 Angstroms.
• Solenoid: 300 Angstroms.
• Chromatin: 700 Angstroms.

12. Gene Mutations

• Impact: Can create new alleles but not new genes.
• Classification:
  • Point mutations: Substitution, deletion, or insertion of a single nucleotide pair.
  • Frameshift mutations: Deletion or insertion of one or more nucleotide pairs.
• Consequences: Most gene mutations are harmless, some can be harmful or beneficial.

13. Enzymes Involved in DNA Synthesis

• Primer synthesizing enzyme: RNA polymerase.
• New strand synthesizing enzyme: DNA polymerase.

14. Variation

• Characteristics:
  • Does not alter the genotype.
  • Uniform in a specific direction.
  • Not heritable.
• Example: Plants grown in sunny areas have darker leaves compared to those grown in shady areas.

15. Reaction Norm

• Broad reaction norm: Quantitative traits. Example: Rice yield, human height.
• Narrow reaction norm: Qualitative traits. Example: Butterfat percentage, flower color.

16. Nucleosome

• Structure: Composed of 8 histone protein molecules surrounded by 146 nucleotide pairs of DNA.
• Function: The basic structural unit of chromosomes, playing a role in chromosome packaging and gene regulation.

17. Gene Regulatory Structure in Bacteria

• Promoter: The transcription initiation site.
• Operator: The regulatory region where repressor proteins bind to block transcription.
• Structural gene: Encodes the protein that performs the function.
• Regulatory gene: Encodes the repressor protein.

18. Genes in the Same Operon

• Characteristics: Transcribed simultaneously, replicated together.
• Example: The Lac operon in E. coli bacteria.

19. Gene Mutation Mechanisms

• G*: Guanine is replaced by adenine (A).
• UV radiation: Causes thymine (T) to bond with thymine (T), leading to the loss of an AT pair.
• 5-bromouracil (5BU): A thymine (T) analogue that can replace AT with GX.

20. Translation Process

• Step 1: The small subunit of the ribosome binds to the mRNA molecule.
• Step 2: Methionine (Met) amino acid is attached to the small subunit.
• Step 3: The large subunit of the ribosome binds to the small subunit.
• Step 4: The ribosome moves along the mRNA, reading the genetic code and linking amino acids in a specific sequence.
• Step 5: When a stop codon (UAA, UAG, UGA) is encountered, Met is detached, and the polypeptide chain is released.

21. Gene Pool

• Definition: All alleles of all genes in a population.
• Representation: Through the relative frequencies of alleles and genotypes.

22. Mating Systems

• Random mating: The most prevalent mating system in animals.
• Non-random mating: Selective mating, inbreeding.

23. Breeding Population

• Key Feature: Polymorphism, variation in genotypes and phenotypes.

24. Hybrid Vigor

• Definition: The phenomenon where F1 hybrids exhibit greater vigor, growth rate, development, and productivity compared to their parents.
• Note:
  • Sometimes reciprocal crosses do not show hybrid vigor, but the reciprocal does.
  • Hybrid varieties are often used for product cultivation because hybrid vigor decreases in subsequent generations.
  • Limitations: Time-consuming, one-time use.

25. Cell Technology Breeding Methods

• Tissue culture: Rapid propagation of valuable plants, creating populations of plants with identical genotypes.
• Somatic hybridization: Creating new varieties carrying the genetic traits of two species.
• Culturing pollen or unfertilized ovules: Producing plants homozygous for all genes.

26. Animal Cell Technology

• Cloning: Generating a new individual with the same genotype as the original.
• Embryo transfer: Dividing one embryo into multiple embryos and implanting them in several individuals, creating a litter of genetically identical offspring.

27. Dolly the Sheep

• Characteristic: Identical to the sheep that donated the nucleus.
• Significance: Demonstrated the feasibility of cloning in animals.

28. Twins

• Identical twins (monozygotic): Same genotype, same sex.
• Fraternal twins (dizygotic): Different genotypes, same or different sexes.

29. Evolution

• Level of Evolution: Depends on the changes in genes on chromosomes.

30. Mutations with Serious Consequences

• Chromosomal structural mutations: Cause serious genetic diseases.

31. Extra-nuclear DNA

• Mitochondrial DNA, chloroplast DNA, bacterial DNA: Circular naked DNA capable of independent replication and transcription from nuclear DNA.
• Genes in mitochondria, chloroplasts: Can function as normal genes.

32. Maternal Inheritance

• Genes on mitochondria: Inherited maternally.
• Genes on Y chromosomes: Inherited paternally.

33. Epistasis

• Complementary gene action: A trait is controlled by multiple non-allelic genes, each gene having a separate but cumulative effect.

34. Phenotypic Ratio of Additive Traits

• 15:1: Phenotypic ratio when a trait is controlled by two non-allelic genes, each with two alleles.

35. Extra-nuclear Inheritance

• Discoverer: Correns.

Note:

• The above knowledge represents fundamental concepts; further exploration of specialized materials is recommended for a deeper understanding of genetics.
• Genetics is a vast field, encompassing various disciplines such as medicine, agriculture, and biotechnology.
• The application of genetics knowledge can enhance our understanding of living organisms, improve human health, and create high-yielding, disease-resistant crops and livestock.

References:

• Biology textbook for 12th grade.
• Specialized genetics websites.