Biology Chapter 15: Chromosomal Inheritance

Chapter 15: The Chromosomal Basis of Inheritance

• DNA is the genetic material, a polymer of nucleotides
• Each DNA consists of sugar (deoxyribose), phosphate, and nitrogenous bases (A, T, G, C)
• Genes are DNA segments coding for molecules (proteins). These are responsible for phenotypic traits.
• Traits are passed to offspring through genes
• Chromosomes are long strands of DNA, wrapped around histones, containing thousands of genes.
• Chromosome 23 determines sex (XX=female, XY=male)
• X and Y chromosomes have different lengths, number, and kinds of protein-coding genes
• Phenotypes can be wild type (common) or mutant (changes from wild type due to a mutation or change of allele).
• Sex-linked genes are unique to either the X or Y chromosome.
• X-linked genes are common in females, while Y-linked genes are usually passed from father to son since there are fewer genes on the Y chromosome.
• Genetic disorders can result from chromosomal abnormalities (e.g., Down syndrome, Turner syndrome).
• X-inactivation in female mammals silences one X chromosome to avoid producing twice the amount of proteins.
• Linked genes tend to inherit together due to a close proximity on a chromosome.
• Crossing over during meiosis promotes genetic recombination, which affects inheritance patterns.

Chapter 16: Molecular Basis of Inheritance

• DNA is the genetic material, a polymer of nucleotides
• DNA has a sugar-phosphate backbone with nitrogenous base pairs (A with T, and C with G).
• The base pairs are held together by hydrogen bonds. DNA strands run in opposite directions (anti-parallel).
• Chargaff's Rule: DNA base ratios vary across species with the same number of bases.
• DNA replication occurs during the S phase of interphase.
• DNA replication starts at replication forks, where the helix splits
• Enzymes like helicase unwind the DNA, topoisomerase reduces tension, and single-strand binding proteins prevent strand rejoining
• DNA polymerase III synthesizes DNA in the 5' to 3' direction, creating leading and lagging strands. Okazaki fragments make up the lagging strand
• DNA Polymerase I removes RNA primers and replaces them with DNA.
• DNA ligase seals the fragments of DNA.
• DNA replication is semi-conservative, where each new DNA molecule has one original strand and one new strand.
• DNA proofreading and repair mechanisms correct errors during replication.

Chapter 17: Gene Expression: From Gene to Protein

• Gene expression is converting DNA information into protein synthesis, using two steps:

• Transcription and translation

• Transcription: Converting DNA into mRNA, occurs in the nucleus in eukaryotic cells and the cytoplasm in prokaryotic cells.

  • Uses RNA Polymerase to produce a pre-mRNA which is processed to mature mRNA.
  • The promoter region with a TATA box guides factors to place themselves before RNA polymerase takes place.
  • RNA Polymerase II unwinds the DNA to initiate the transcription.
  • Proceeds in the 5' to 3' direction continuously.
  • A sequence called the Polyadenylation signal (CAAAUAAA) in the pre-mRNA signals termination.
  • Final product includes a 5' cap and 3' poly-A tail to help with stability.

• Translation: Converting mRNA into a polypeptide chain. This occurs in the cytoplasm (ribosomes).

• mRNA is read by ribosomes in triplets of nucleotides (codons).

  • Each codon specifies a particular amino acid.
  • tRNA molecules carry specific amino acids to the ribosome based on the mRNA codons' anticodons.
  • A peptide bond forms between amino acids as the ribosome moves along the mRNA.
  • Codons (UAA, UAG, UGA) signal the end of the polypeptide and release factor detaches.

• Post-Translational modifications help to finish the protein folding and structure.

• Polyribosomes allow for multiple ribosomes to translate the same mRNA at the same time.

Chapter 22: Descent with Modification: A Darwinian View of Life

• Evolution is a process of genetic change in organisms over time.
  • Natural selection is a mechanism for evolution in which individuals with traits better suited to their environment are more likely to survive and reproduce. This helps to increase fitness.
  • Adaptation is a trait that increases an organism's fitness in its environment.
• Evidence for Evolution:
  • Direct observations (soapberry bug beak length changes, drug-resistant bacteria)
  • Homology (similarities in anatomical structures and development suggesting common ancestry). Vestigial structures are leftovers from previous functions
  • Fossil records (transition fossils show intermediate forms of evolution). The fossil record is a chronological record.
  • Biogeography (the geographic distribution of species). Species are found in areas in which their ancestors were before geographic events.
• Artificial Selection is where humans select and breed specific traits in plants or animals.
• Phylogenetic Trees show evolutionary relationships between organisms, representing common ancestors and branching patterns. Nodes represent an unknown common ancestor for two lineages.

Additional Information (General)

• Mutations: Changes in DNA sequences. They can be beneficial (supporting adaptation), neutral, or harmful.
• Point mutations are changes in a few nucleotides within a DNA sequence. If they happen in a gamete, future generations may be impacted. This may lead to genetic disorders.
• Different types of mutations include nucleotide pair substitution (silent, missense, nonsense), insertions, and deletions. These can cause frameshifts resulting in an entire shift of where the codons are read.