A3.1:  Diversity of Organisms

Theme:  Unity and Diversity

The tools and methods used to study biodiversity demonstrate how scientific investigation uncovers both themes:

• Genome sequencing reveals both the shared genetic heritage that unites all life and the specific mutations and rearrangements that distinguish different species and populations
• Environmental DNA barcoding techniques can rapidly identify the incredible diversity of species in any habitat while using the same universal genetic principles that apply to all organisms
• Karyotyping analysis provides testable hypotheses about evolutionary relationships, such as the fusion event that created human chromosome 2, showing both our connection to other primates and our unique genetic features
• The ability to create systematic identification tools for local species demonstrates both the shared morphological principles that allow classification and the unique combinations of traits that distinguish each species​

Unity:

• ​All organisms are classified using the same two-part naming system that identifies genus and species, providing a unified framework for organizing life's diversity across all cultures and languages
• All organisms store genetic information in DNA using the same four-base genetic code
• Whether using morphological or biological species concepts, the fundamental idea that organisms sharing similar traits and evolutionary history can be grouped together applies universally across all life forms
• All diploid organisms have even numbers of chromosomes organized in homologous pairs, and all use similar mechanisms for chromosome packaging and inheritance
• Genome sequencing reveals that all organisms share fundamental genetic sequences and metabolic pathways, confirming the unity of life through common descent from ancient ancestors
• The same molecular techniques can identify species across all taxonomic groups, from environmental bacteria to complex multicellular organisms

Diversity:

• No two organisms are identical in all traits, creating the raw material for evolution and adaptation while making each individual unique within its species
• ​The challenge of defining a species reflects the complex ways organisms have diversified, with some reproducing sexually, others asexually, and bacteria transferring genes horizontally
• Different species have evolved dramatically different chromosome numbers, from single chromosomes in some organisms to hundreds in others
• Organisms show enormous diversity in genome size that does not correlate with complexity
• The continuous process of populations diverging into new species creates an ever-expanding tree of life, with the arbitrary nature of species boundaries reflecting the dynamic nature of evolutionary change
• Different species show unique chromosome banding patterns, lengths, and centromere positions 

Guiding Questions:  
Guiding questions help students view the content of the syllabus through the conceptual lenses of both the themes and the levels of biological organization.

• What is a species?
• What patterns are seen in the diversity of genomes within and between species?

​
Linking Questions:  
Linking questions strengthen students’ understanding by making connections between topics.  The ideal outcome of the linking questions is networked knowledge.

• What might causes a species to persist or go extinct?
• How do species exemplify both continuous and discontinuous patterns of variation? ​​

Key Terms to Know: * higher level only

Arbitrary
Asexual Reproduction*
Banding Pattern
Base Sequence
Binomial
Biodiversity*
Biological Species Concept
Centromere
Chromosome Number
Continuous Variation
Cross Breeding*
Dichotomous Key
Dichotomous Key*
Diploid
Discrete Variation

Divergence
Diversity
Diversity
DNA Barcode*
Environmental DNA*
Eukaryote
Fertile
Genome
Genus
Horizontal Gene Transfer*
Interbreeding
Interspecies
Intraspecies
Karyogram
Karyotype

Linneaus
Morphological Species Concept
Morphology
Organism
Personalized Medicine
Population
Sexual Reproduction
Single-Nucleotide Polymorphism (SNP)
Speciation
Species
Taxonomy
Unity
Variation
Whole Genome Sequencing

A3.1.1— Variation between organisms as a defining feature of life. 

• Define organism.
• Define variation.
• List sources of genetic variation within a species. 
• Compare discrete and continuous variation. 
• Compare variation within and between species. ​

A3.1.2— Species as groups of organisms with shared traits.

• Define species according to the morphological species concept.

A3.1.3—  Binomial system for naming organisms. 

• Define binomial nomenclature.
• State four rules of binomial nomenclature formatting.
• Outline why the binomial naming system is used in science rather than local names.

A3.1.4— Biological species concept.

• Define species according to the biological species concept.
• Describe limitations of the biological species concept, with mention of hybrids and geographical separation. ​

A3.1.5— Difficulties distinguishing between populations and species due to divergence of non-interbreeding populations during speciation.

• Define speciation.
• Explain the difficulties in distinguishing between populations and species during speciation. ​

A3.1.6— Diversity in chromosome numbers of plant and animal species.

• State that chromosome number is a distinguishing characteristic of a species.
• Explain why the typical number of chromosomes in a diploid cell is an even number.
• State the number of chromosomes in humans and in chimpanzees. ​
• Evaluate the evidence for the hypothesis that chromosome 2 in humans arose from the fusion of chromosomes 12 and 13 with a shared primate ancestor.
  

A3.1.7—  Karyotyping and karyograms. 

• Define karyotype and karyogram.
  
• List the characteristics by which chromosomes are paired and arranged on the karyogram.
• Define autosome and sex chromosome. 
• Deduce the sex of a human individual given a karyogram.

A3.1.8—  Unity and diversity of genomes within species.

• Define genome, gene and allele.
  
• Outline the cause and effect of “single-nucleotide polymorphisms” in genomes.

A3.1.9— Diversity of eukaryote genomes.​​

• Describe reasons why a larger genome does not necessarily indicate presence of more genes. 
• Compare variation in genomes sizes and gene sequences within and between species.​ ​

A3.1.10— Comparison of genome sizes.

• State the units for measuring genome size. 
• Use a database to compare genome sizes to determine if there is a relationship between the number of genes in a species and the species complexity in structure, physiology and/or behavior.

A3.1.11— Current and potential future uses of whole genome sequencing.

• Define “sequence” in relation to genes and/or genomes.
• State that technological improvements have sped the DNA sequencing process.
• List applications of genome sequencing.
• Discuss ethical considerations of genome sequencing.

AHL A3.1.12— Difficulties applying the biological species concept to asexually reproducing species and to bacteria that have horizontal gene transfer. 

• Compare sexual and asexual reproduction. 
• Discuss difficulties in applying the biological species concept to asexually reproducing species such as dandelions. 
• Define horizontal gene transfer. 
• Discuss difficulties in applying the biological species concept to bacteria that have horizontal gene transfer.​

AHL A3.1.13— Chromosome number as a shared trait within a species.

• Explain how sexual reproduction maintains chromosome number within a species. 
• Outline the mating of a donkey and a horse to produce a sterile mule as an example of cross-breeding between closely related species producing sterile offspring because of differences in parent chromosome numbers. ​

AHL A3.1.14— Engagement with local plant or animal species to develop a dichotomous key.

• Explain the use of a dichotomous key in the identification of a specimen.
• Demonstrate use of a dichotomous key given an unknown specimen.
• Develop a dichotomous key for a local plant or animal species.

AHL A3.1.15— Identification of species from environmental DNA in a habitat using barcodes.

• Define “DNA barcode” and “environmental DNA.”
• Outline the use of “DNA barcoding” to identify species from environmental DNA.
• List applications of DNA barcoding using environmental DNA.