Biology Unit 5

• Speciation


  Two or more distinct species forming from a single ancestral species during an extended period of reproductive isolation and divergence
• New alleles are introduced in a population through mechanisms such as mutation, gene flow, genetic drift, and selection. They can change the allele frequencies and observed characteristics of a population over time.
• If the population is large or spread out across a wide area, it is possible for different parts of the population to change in different ways
• Speciation is more likely to occur if alleles are unevenly distributed, with some alleles found more often in certain regions.
• Morphological species concept


  Determining species based on observable traits
• The morphological species concept is subjective and unreliable, but this method is used in certain situations
• Biological species concept


  A species is a group of organisms that interbreed and produce fertile offspring under natural conditions
• Two populations that cannot or will not interbreed are said to be reproductively isolated from each other, and the populations are considered separate species by the biological species concept
• Reproductive isolation can be caused by a variety of mechanisms that prevent two groups of organisms from interbreeding. As a result, the groups stop exchanging alleles with each other and begin to diverge
• Reproductive barriers


  • Prezygotic
  • Postzygotic
• Prezygotic reproductive barriers


  • Geographic isolation
  • Temporal isolation
  • Ecological isolation
  • Behavioral isolation
  • Mechanical isolation
  • Gametic isolation
• Postzygotic reproductive barriers


  • Hybrid inviability
  • Hybrid sterility
• Biological species concept disadvantages:

  • not applicable to asexually reproducing organisms - prokaryotes
  • extinct organisms known only from the fossil record
• Phylogenetic tree


  A branching diagram that describes the inferred evolutionary relationships between select groups of organisms

  
• Phylogenetic trees represent hypotheses about evolutionary relationships, and were originally constructed using observable traits but are now usually based on genetic information

  
• Nodes

  Branching points on phylogenetic trees that represent the most recent common ancestor of descendant lineages
• Branches


  Lines on a phylogenetic tree that represent evolving lineages

  
• Synapomorphies

  Traits that are present in lineages that descend from a node or branch, also known as shared derived characters
• Monophyletic groups


  Consist of a common ancestor and all of the lineages that descend from that ancestor
• Evolutionary relatedness


  Determined by most recent common ancestry, not by perceived similarities, distance on the phylogenetic tree, or number of nodes between organisms

  
• Homology


  Traits that are inherited from a common ancestor
• Analogy


  Traits that are similar due to convergent evolution, not inheritance from a common ancestor
• The process by which new species arise is called speciation.
• Genetic drift refers to changes in allele frequencies within a population over time due to chance events.
• Founder effect occurs when only a small subset of individuals from one population migrates to another area and establishes a new population.
• Bottleneck effect results from a sudden decrease in population size, (can occur due to gamete sampling or natural disasters.)
• Gene flow refers to the movement of genes into or out of a population through migration.
• For natural selection to act on a trait, there must be variation for that trait. The trait must be heritable.
• Genetic drift has a larger impact on smaller populations.
• Mutation is the original source of variation but has a low impact on a population unless paired with another evolutionary mechanism.
• Hardy-Weinberg Principle states that allele and genotype frequencies will remain constant under certain conditions:

  1. no mutations occur
  2. randomly mating
  3. no trait advantages
  4. large populations
  5. no migration (of genes/alleles)
• The equations of Hardy-Weinberg are limited to:

  1. sexually reproducing populations
  2. autosomal genes
  3. no mixing between generations
  4. genes with only 2 alleles
  5. diploid organisms
• What are some examples that violate the Hardy-Weinberg equations?

  1. self-fertilization or asexual reproduction
  2. sex-linked alleles
  3. mixing of different generations
  4. genes with more than 2 alleles like blood (ABO)
  5. polyploidy organisms
• What makes the Hardy-Weinberg Principle unrealistic?


  Populations will never meet all of the assumptions in place. There will be mutations, nonrandom mating, selection, genetic drift, or gene flow in any real population.
• What are the mechanisms of Evolution?

  mutation, gene flow, genetic drift, selection
• Types of Selection (it's nonrandom):

  1. Natural: natural variation in every population; some traits are environmentally specific = higher fitness
  2. Artificial: any selection by human intervention (corn crop, dogs)
  3. Sexual: favorable to traits intended to attract mates not necessarily providing higher fitness; can sometimes decrease survivability
• Sexual Selection description:

  • Females: naturally invest more time and energy into offspring; produce a limited amount of offspring - must choose traits that increase fitness
  • Males: ability to produce indefinite number of offspring; mate with any available females leading to competition between males of the same species
• Natural Selection types:

  1. Directional: 1 extreme trait provides greater fitness
  2. Stabilizing: Intermediate trait is more favorable and produces greater fitness
  3. Disruptive: extreme traits simultaneously provide greater fitness
• • Geographic: physical separation
  • Temporal: different reproduction times
  • Ecological: environmental preference
  • Behavioral: prevention by specific behavior
  • Mechanical: physical inability - organs
  • Gametic: gametes are incompatible
• • Hybrid inviability: resulting embryos do not develop
  • Hybrid sterility: healthy embryo doesn't have the ability to reproduce