Biology Lecture 15: Evolution and Aneuploidy

Evolution and Genetics

• Diversity in populations allows adaptation to changing environments and increases the likelihood of survival in the face of selective pressures.

Aneuploidy

• Aneuploidy refers to an abnormal number of a particular chromosome.
• Examples of aneuploid conditions in humans include:
  • Down syndrome (Trisomy 21)
  • Patau syndrome (Trisomy 13)
  • Edwards syndrome (Trisomy 18)
  • Klinefelter syndrome (XXY)
  • Turner syndrome (XO)
  • XYY and XXX variations

Nondisjunction

• Nondisjunction is the failure of chromosomes to separate properly during meiosis.
• This can result in an abnormal number of chromosomes in the resulting gametes.

Polyploidy

• Polyploidy refers to the possession of multiple sets of chromosomes.
• Some forms of polyploidy can lead to infertility due to problems in meiosis and gamete formation.
• Other forms, such as allopolyploidy, may result in fully fertile individuals.

X-Inactivation

• X-inactivation is a process by which one of the X chromosomes in female mammals is inactivated to ensure dosage compensation between males and females.
• X-inactivation prevents overexpression of X-linked genes in females and ensures equal gene expression between the sexes.
• X-inactivation leads to mosaic patterning in females because the inactivation of one X chromosome occurs randomly in each cell during early embryonic development.

Central Dogma of Molecular Biology

• The Central Dogma of Molecular Biology describes the flow of genetic information within a biological system.
• Genetic information is transferred from DNA to RNA (transcription) and then from RNA to protein (translation).

Transcription

• Transcription is the process by which RNA is synthesized from a DNA template.
• The template strand of DNA serves as the template for transcription.
• The three stages of transcription are:
  • Initiation: RNA polymerase binds to the promoter region of the DNA, forming a transcription initiation complex.
  • Elongation: RNA polymerase synthesizes RNA in the 5' to 3' direction along the template strand.
  • Termination: RNA polymerase recognizes termination signals, causing it to dissociate from the DNA.

Comparative Genomics

• Comparative genomics allows us to understand commonalities and differences between genomes, revealing conserved biological functions and organism-specific traits.
• Sequences are compared by aligning them next to each other and identifying points where sequences are the same.
• Comparing genomes within a species can reveal differences associated with disease, individual characteristics, and evolutionary history.
• Comparing genomes between species helps identify shared and unique genetic features, shedding light on evolutionary relationships and biological functions.

Microbiology

• Microbes exploit different environments by tuning their metabolic processes and utilizing available resources.
• The four key trophic groups of microorganisms are:
  • Chemoautotrophs
  • Chemoheterotrophs
  • Photoautotrophs
  • Photoheterotrophs
• The majority of the microbial world is uncultured because many microorganisms cannot be isolated in pure culture.
• Identification is often done using genetic 'fingerprints' such as 16S rRNA sequences, revealing a vast diversity of uncultivated bacteria.

Microbial Metabolism

• The two main areas of focus in microbial metabolism are:
  • Energy acquisition (e.g., harvesting electrons)
  • Building block acquisition (e.g., carbon fixation)
• Cable bacteria live in anoxic environments but create conductive filaments to shuttle electrons to oxic zones, allowing them to breathe oxygen while residing in anaerobic conditions.

Human Microbiome Project

• The primary goals of the Human Microbiome Project (HMP) were to understand the human microbiome and its role in health and disease.

Fecal Microbiota Transplantation

• Fecal microbiota transplantation is the process of transplanting fecal bacteria from a healthy donor into a patient, primarily used to treat multiple recurrences of Clostridium difficile infection (CDI).
• Modifying the gut microbiome can influence various aspects of health, such as enhancing the immune response, altering metabolism, and affecting susceptibility to pathogens.

Viruses

• Viruses consist of genetic material (either DNA or RNA) and a protein coat called a capsid.
• Some viruses also have an envelope of lipids that surrounds the protein coat.
• The three types of viral capsid symmetry are:
  • Helical
  • Icosahedral
  • Complex