Diversity of Organisms

Classification of Species

    Broadest to most Specific:

  • Domain
  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species

    Binomial Nomenclature:

  • Formal system of naming species
  • Consists of genus and species name
  • Underline the name when writing on paper or italicize when typing
  • Example: Homo sapien
    • Capitalize genus name
    • Homo → genus
    • Sapien → species

What is a Species?

There are two different ways to define species: morphologically or biologically.


    Morphological Definition

  • Species - An unchanging group of organisms with clear internal and external structural differences from other species
    • Based on shared morphological characteristics
    • The idea that organisms of the same species tend to look similar

  • Issues with this:
    • There is no clear way to define how similar a species looks to one another
    • In addition, how do we define different species that look extremely similar to each other
    • Also it violates evolution, as species are not unchanging

    Biological Definition

  • Species - A group of organisms that can breed and produce offspring

  • Issues with this:
    • The Case of Ligers - tigers and lions can reproduce but are different species
    • Asexuality - some animals can reproduce alone (asexually)
    • Extinction - extinct animals’ reproduction patterns cannot be determined by fossils
    • Ring Series - ring series involve a series of interlinking breeding populations with incompatible ‘ends’

Speciation

  • If two populations of the same species don’t interbreed for a prolonged period of time, they may diverge over time as they evolve in their respective environments
  • Population - a group of organisms of the same species living in the same place at the same time
  • Over time, separate groups may grow apart so far that they may not seem to be genetically similar anymore, thus forming a new species

Chromosome Numbers

  • Generally, different species have different chromosome numbers
  • Sexually reproducing species usually have even number of chromosomes due to the fact that they must combine two cells

Karyotyping

  • Chromosomes can be classified by banding patterns, length, and location of centromere
  • Karyotype - organized profile of a person’s chromosomes
    • Two chromosomes specify sex, while the others are arranged in size
    • This arrangement helps scientists quickly identify chromosomal altercations that may result in genetic disorders
    • To make, scientists take a picture of the chromosome from one cell, then sort them

Genomes

  • Genome - All the genetic information of an organism
  • Entire sequence of base pairs on each chromosome
  • Organisms of the same species share most of their genome
  • Genome sequencing:
    • Determines the order of bases in the genomes of organisms
    • Uses: research of evolutionary relationships, genomic medicine (specified to an individual)
  • The variation of genomes is essential for life; natural selection and evolution could not happen without it

Relation of Chromosome Numbers to Life

  • Chromosome numbers can increase or decrease with evolution
  • Changes in chromosome numbers are rare and usually do not occur over millions of years
  • Many different species have diverse chromosome numbers, ranging from 2 to hundreds
    • Some species may have many small chromosomes
    • Others may have few large chromosomes

Single-Nucleotide Polymorphisms (SNP)

    Alleles

  • Often within species, alleles of a gene differ from each other in base sequences
  • Usually, only one or a very small number are different
  • Sometimes larger sections of a gene become altered, but this usually results in a loss of gene function

    SNP

  • Position in a gene where more than one base may be present
  • The average human has 1 SNP in around 650,000 bases
  • At least 1% of individuals have to have the different base pair in order for the position to be an SNP
    • Child is homozygous if parental alleles have the same base at an SNP
    • Child is heterozygous if parental alleles have a different base at an SNP

    Eukaryotic Genome Diversity

  • Two populations of a species will have differences in their base sequences
  • As populations diverge to form separate species, more differences will accumulate
  • However, sometimes changes in base sequences are infrequent
  • These tend to be among genes with a vital function that does not change
    • As a result, distantly related species may have few (or no) base sequence differences
  • Species diverted from a common ancestor have thus developed differences in their genetic make-up, especially when they adapted to different ways of life