BIOL202 Lesson 10

• 1. X-linked inheritance


  Genes found in sex chromosomes; X and Y carry different sets of genes
• 1. X-linked traits


  • Traits controlled by X-linked genes
  • X-linked gene: a gene on X chromosome
• Red-green colour blindness

  • X-linked recessive disorder, common in males (22% Caucasian), affects ability to perform tasks requiring colour detection
• Hemophilia


  • X-linked recessive disorder, causes bleeding and clotting issues, even minor injuries can be life-threatening, treated with blood clotting factors
  • Also called "Royal Disease"
• Polygenic inheritance


  Single trait controlled by multiple genes with additive effect. Usually quantitative traits like height, skin colour. Complex diseases like diabetes, schizophrenia
• What are complex diseases?


  Caused by multiple genetic (polygenic) and environmental factors; develops when cumulative risks outweigh cumulative anti-risks
• Evolution


  Process of species change over time, by which existing organisms develop from ancestral forms
• Population growth

  Grows exponentially, but availability of resources grows arithmetically, leading to competition for resources
• Conditions for evolution by natural selection

  • Variation: particular trait within population
  • Heritability: variation must be inheritable
  • Differential reproductive success: individual with one version of the trait produces more offspring than those with different traits
• Evidence for evolutionaccording to Darwin

  • Fossil records: shows species evolved in the past
  • Biogeography: geographic species distributions reflect their evolutionary histories; individuals who live nearby are more similar than those who live far away
  • Comparative anatomy and embryology: comparison of bone structure and function between different species
  • Molecular biology: species with similar DNA sequences are closely related
  • Laboratory and field experiments: experiments allow us to know more about a specie's population and environment
• Molecular clock


  Used to estimate time since common ancestor, e.g. humans and monkeys shared a common ancestor 23 million years ago
• Agents of evolutionary change

  • Mutation: ultimate source of genetic variation in population
  • Genetic drift: Alleles frequency changes by random chance
  • Migration: group of individuals exist in a separate location
  • Natural selection: 3 criteria --> adaptations, fitness, and sexual selection
• Founder effect?


  Type of genetic drift; small subgroup of larger population establishes itself as separated and isolated completely; this leads to an increase in frequency of certain alleles in the subgroup
• What is a population bottleneck?


  A type of genetic drift; extreme and rapid environmental changes kill most individuals in population; survivors have different allele frequency than the original population
• Fitness


  Measure of reproductive output compared to other individuals in a population, depends on specific environment
• Sexual selection

  Natural selection for mating success, leads to reproductive strategies like male peacock displays
• Observations made by Darwin during his voyage?

  • Fossil records
  • Similar species, different places
  • Species are evolving
• What are the three possible genotypes/phenotypes of an X-linked gene in females?

  • xAxA: dominant trait
  • xAxa: dominant trait
  • xaxa: recessive trait
• What are the two possible genotypes/phenotypes of an X-linked gene in males?

  • xAy: dominant trait
  • xay: recessive trait