Bio b355 final

• Biological evolution


  Inherited change in properties of groups of organisms over generations, descent with modification
• Framework of understanding biological diversity

  • Includes features and processes that are essential for human health and welfare
• Killer X chromosome in Drosophila flies

  Causes higher rate of female offspring
• Inheritance of killer X chromosome

  Gene on X chromosome - males only have 1 X, distorted X chromosome on female are more likely to get it
• Hypotheses for why a killer X chromosome would evolve

  • Selfish gene
• Why a gene on an X chromosome evolve to destroy sperm that carry a Y chromosome

  Insure survival of the selfish gene
• A killer X chromosome could evolve without benefitting the organism
• Why an X chromosome evolve to be preferentially inherited, relative to other X chromosomes
• Population genetics


  Study of naturally occurring genetic differences among organisms
• Polymorphism


  Study of genetics within species, variation within an allele
• Divergence


  Study of genetics between species
• Spandrels


  Space between arches there to help hold them up, used as a metaphor for traits that are not directly selected for
• Panglossian


  Too much faith/concern with natural selection, metaphor from Voltaire's novel "Candice"
• Adaptationist


  Regards natural selection as so powerful and without constraints that it becomes the primary cause of all organic forms, function and behaviour
• To demonstrate that something is adaptive, and not just telling a 'Panglossian' just-so story, one needs to show that the phenotype causes a change in fitness
• To determine the adaptive function of a trait, one needs to show that the phenotype causes a change in fitness
• Microcephalin and ASPM


  Genes involved in brain cell division and neural cells
• Phenotype of broken microcephalin and ASPM genes


  Improper proteins, leading to smaller brain size
• There is genetic variation in microcephalin and ASPM in humans
• The variation in microcephalin and ASPM shows geographic differences, likely due to genetic drift
• Haplotype


  A group of alleles in an organism that are inherited together from a single parent
• There is no statistical difference in head size between individuals with common haplotypes of microcephalin and ASPM
• The variants in microcephalin and ASPM do not appear to have a phenotypic effect
• Natural selection is the consistent difference in fitness among different classes of biological entities
• Adaptation


  A characteristic that enhances the survival or reproduction of organisms that have it, relative to alternative character states
• Adaptive


  Referring to a newer, more beneficial version of a trait
• Fitness


  The number of offspring an individual leaves in the next generation
• To study/measure/infer/demonstrate adaptation, natural selection, and fitness, one observes traits of populations over time, looking for genetic, reproductive, and survival changes
• Adaptations to high altitude found in Tibetans

  • Low chronic mountain sickness
  • Lower [hemoglobin]
  • Lower infant mortality and higher fertility
  • Lower incidence of preeclampsia
• The evidence for adaptation in Tibetans is the presence of different alleles in the population causing changes in phenotype
• Cynthia Beall and colleagues found an association between variation in the EPAS1 gene and adaptation to high altitude in Tibetans, with the EPAS1 variant being associated with lower levels of hemoglobin
• EPAS1 gene


  Codes for a transcription factor that regulates in response to low oxygen
• A genome scan/Manhattan plot can be used to identify variation at certain positions on a chromosome that are statistically significantly associated with a phenotype
• Emilia Huerta-Sánchez and colleagues concluded that the EPAS1 variant common in Tibetans originated from Denisovans
• The evidence used by Huerta-Sánchez et al. was aligning nucleotides from Chinese and Tibetan samples with a Denisovan sample to find matching sequences
• Denisovans were an unknown hominin species discovered through ancient DNA analysis
• Introgression


  The transfer of genetic material from one species into the gene pool of another by the repeated backcrossing of an interspecific hybrid with one of its parent species
• Hybridization


  The interbreeding of individuals from two genetically distinct populations, or races, to produce an offspring
• Svante Pääbo won the Nobel Prize in Physiology or Medicine for his discoveries concerning the genomes of extinct hominins and human evolution
• Most new mutations are deleterious, while most mutations that persist are beneficial