A3.1 Diversity of Organisms

A3.1.1 Variation Between Organisms As a defining feature of life

1. No two individuals are identical in all their traits 

   1. Even monozygotic twins have variation in epigenome (detailed in D2.2).

2.  The diversity of organisms adds to the richness of the natural world, and variation allows evolution by natural selection to occur.

What are species?

1. Carl Linnaeus pioneered calling a species “ a group of organisms with shared morphological traits. ” 

2. Claimed it was evidence of “ a creator ”

A3.1.3  Binomial System For Naming Organisms 

1. Written as Genus species, and if mentioned once already, as G. species (underline when handwritten). 

2. Species in the same genus have similar traits

effects of organizing organisms into species

a species is a group of organisms that can successfully interbreed and produce fertile offspring. 

1. Explains how a group of individuals can exist in a coherent unit and hence share genes in a gene pool. 

2. The biological species concept works well with some groups of organisms, but exceptions exist (ex., offspring produced by hybridization that are fertile - Lions x Tigers, for instance, but they are not a species).

 Difficulties Distinguishing Between Populations And Species

1. Two geographically isolated populations can still be the same species as long as they share the same DNA and physical traits.

2. Speciation is a slow, continuous, and ambiguous process: 

   1. First, there is no interbreeding between two populations. 

   2. Second, genetic and physical differences build up. 

   3. Third, eventually, they become so different that they can no longer interbreed.

A.3.1.7 Karyotyping and Karyograms

1. Chromosomes are best observed during metaphase - cells are stained, placed on a slide, and burst open to spread the chromosomes. 

2. A photograph is taken, and chromosomes are digitally rearranged to create a karyogram. 

3. Chromosomes are classified into pairs based on

   1. Banding patterns 

   2. Size 

   3. Centromere 

   4. position

Application of skills: Students should 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. NOS: Students should be able to distinguish between testable hypotheses such as the origin of chromosome 2 and non-testable statements

A.3.1.8 Unity and Diversity of Genomes Within Species

1. Members of the same species tend to have the same genes, in the same order on each chromosome. 

2. Allows for chromosome pairing and recombination during meiosis without omitting/duplicating genes. 

3. Variations of the same gene (alleles) allow for variation across members. SNPs (single-nucleotide polymorphisms) are positions in the genome where more than one base is common in the population (must occur in at least 1% of the population) and thus give variation. 
   Genome: entire set of genetic material in an organism.

   • measured in base pairs (bp) or megabases (Mb).

Includes: 

• all of an organism’s DNA

• both coding regions (genes) and non-coding regions

• All individuals in a species share most of their genome, ensuring: 

  • Similar body structures

  • Biochemical processes (e.g., enzymes, hormones)

  • Inherited traits typical of that species

• C-value paradox: many simple organisms have more DNA than complex ones.

 a species can havelots of DNA without having more genes or being more complex.

A.3.1.9 Diversity of Eukaryotic Genomes

1. Genomes vary across species in their: 

   1. Genome size. 

   2. Base sequence.

A.3.1.10 Comparison of Genome Sizes

1. Genome size refers to the total amount of DNA in a species. 

   1. Large genome ≠ more genes nor greater complexity of the organism. 

2. There are online databases you can access to view genomes of various species.

tudents should extract information about genome size for different taxonomic groups from a database to compare genome size to organism complexity

 Current and Potential Future Uses of Whole Genome Sequencing

1. Whole genome sequencing (determining the entire base sequence of an organism ’ s DNA) is now much faster and cheaper. 

2. Currently, it can be used to determine evolutionary relationships. 

   1. In the future it can be used to develop personalized medicine.

A.3.1.12 Difficulties in applying the biological species concept to asexually reproducing species and to bacteria that have horizontal gene transfer

Asexually Reproducing Species	Bacteria with Horizontal Gene Transfer
Asexually reproducing species produce offspring identical to the parent - they do not interbreed.  Technically, each offspring is a new species.	In horizontal gene transfer, genes move between different species (even distantly related ones).  Species are not isolated gene pools.

A.3.1.13 Chromosomes Number as a Shared Trait Within A Species 

1. Organisms with different chromosome numbers will produce offspring that have problems carrying out meiosis. 

   1. Gametes only have one set of chromosomes - if the other gamete doesn ’t have the other complete set of chromosomes, some will not pair up as bivalents.

A.3.1.14 Engagement With Local Plant or Animal Species to Develop a Dichotomous Key 

1. A dichotomous key allows for organizing characteristics in a step-by-step manner. 

   1. By using binary choices for each step, options clearly separate the group into distinct categories, becoming more and more specific with each step.

A.3.1.15.  Identification of Species from Environmental DNA in a Habitat Using Barcodes

1. DNA barcode: Short sections of DNA from a known gene that are unique enough to identify a species. 

   1. Identified by small tissue samples. 

2. Environmental DNA (eDNA): DNA shed by organisms into the environment (skin cells, hair, saliva, waste in water, soil, snow, etc.). 

   1. Non-invasive and efficient method of conservation, ecological studies, and tracking biodiversity.

Case study: link between chimpanzees and humans

• humans have 23 pairs, while other great apes have 24 pairs

• Their bandings match

• Telomeres present where the two chromosomes would have fused

• both have acrocentric shape
  

limitations to biological concept 

Limitations: 

• interbreeding is not applicable to asexual organisms

• Fossils don’t reveal reproductive behaviors (unable to test whether extinct organisms could interbreed)

• There are exceptions → can interbreed and produce fertile hybrids (e.g., lions x tigers) 

• Organisms may not interbreed simply due to physical separation

• Populations of species that can interbreed with neighboring groups but not with distant ones in the same ring

Conflicts with: 

Horizontal gene transfer: genes can be transferred across species → makes boundaries between species confusing

diversity in chromosome numbers of plant and animal species

• Chromosomes: thread-like structures made of DNA and protein found in the nucleus of eukaryotic cells.

  • Carry genetic information in the form of genes.

• Most organisms have chromosomes in pairs – one from each parent.

• The diploid number (2n): the total number of chromosomes in a somatic (body) cell.

  • 2 complete sets of chromosome 

  • Always an even number of chromosomes  because chromosomes are in pairs.

  • Usually the same number in same species

The haploid number (n): is half the diploid number, found in gametes (sperm/egg).

Comparison of Genome Sizes

When using a database: 

• Sort by group (plants, animals, fungi, protists)

• Compare average sizes

• Look for exceptions to the genome size vs. complexity trend

• Whole genome sequencing involves determining the complete DNA sequence of an organism’s genome at a single time.

Uses: 

• Comparing genomes across species to study common ancestry, mutation rates, and speciation

• Identifying genetic mutations responsible for inherited diseases like cystic fibrosis, BRCA (breast cancer risk), etc.

• Sequencing viruses (e.g., SARS-CoV-2) to monitor variants and outbreaks

• Understanding plant and livestock genomes to improve yield, disease resistance, 

Next-generation sequencing techniques: mix of laboratory hardware, chemical markers and powerful software to increase the speed and decrease the cost of sequencing people's genomes