Diversity of organisms, A3.1

• What is an organism?

  An organism is any biological system that functions as an individual life form. All organisms are composed of cells.
• What is a population?

  A population is a group of organisms of the same species in the same area. Even though they are the same species, the individual organisms of the population vary from each other.
• What is a community?

  Communities are the populations of two or more different species occupying the same geographical area at the same time. There is great variation between different species.
• What is a species?

  A species is a group of organisms that share key structural (morphological), genetic, and functional traits, and typically:

  - Interbreed to produce fertile offspring (in sexually reproducing organisms)

  - Share a common gene pool - Are reproductively isolated from other such groups
• What is variation?


  - Variation is a defining feature of life.

  - Variation refers to differences between members of a group. It results in natural selection, which drives evolution.

  - Genetic variation arises from DNA differences (e.g., mutations, meiosis).

  - Environmental variation comes from external factors (e.g., sunlight, nutrition).
• Why is variation essential?

  - Basis of Evolution: Natural selection acts on variation - fitter traits are inherited.

  - Basis of Classification: Organisms are grouped based on similarities and differences.

  - Raw Material for Speciation: Discontinuous variation can lead to the formation of new species.
• What is discrete variation?

  Discrete variation is the variation of traits that can be put into distinct qualitative categories. It can be shown on a bar chart.

  Discrete variation is caused by only one or a few genes. They can also be influenced by environment, although not significantly.
• What is continuous variation?

  Continuous variation is the variation of traits that vary along a quantitative continuum. Most types of biological variation are continuous. It can be shown as a histogram.

  Continuous variation is caused by complex interaction between many different genes (polygenis), with the environment playing a significant part in the expression of the phenotype.
• What is somatogenic variation?

  Somatogenic variation is the variation of traits that are acquired during one's lifetime.
• What is blastogenic variation?

  Blastogenic variation is the variation of traits that arise from genetic differences in gametes.
• What is meristic variation?

  Meristic variation is the variation of traits relating to the number of body parts in an organism.
• What is substantive variation?

  Substantive variation is the variation of size, shape or colour.
• What is Linnaeus's system of classification?

  Linnaeus's system of classification was the first formal system of grouping organisms.

  1- Kingdom

  2- Phylum

  3- Class

  4- Order

  5- Family

  6- Genus

  7- Species
• What is the morphological species concept, and what are some issues with it?

  A species is a group of organisms that look similar and can be distinguished from other groups based on shared, observable traits (morphology).

  However, there are issues with this method of classification via morphology:

  - Convergent evolution

  - Cryptic species

  - Intraspecific variation

  - Subjectivity
• What is binomial nomenclature?

  Species are named using binomial nomenclature.

  Here, two terms are used.

  - The first term indicates the genus

  - The second term indicates the species
• What are the rules for formatting binomial nomenclature?

  - Genus name begins with capital letter

  - Species name begins with lowercase letter

  - The name is in italics if types, underlined if written

  - After its first use, the genus name is abbreviated to its first letter.
• What are some reasons for the use of binomial nomenclature?

  - Reflects evolutionary relationships between organisms

  - Is a standardised form of communication between scientists
• What is the biological species concept?

  A species is a group of actually or potentially interbreeding populations which are reproductively isolated from other groups.
• What are the limitations of the biological species concept?

  - Naturally and artificially produced hybrids

  - Variation across geographical ranges

  - Divergence during speciation

  - Practical challenges of testing

  - Asexually reproducing organisms

  - Geographical isolation
• How are hybrids limitations for the biological species concept?

  Hybrids are the offspring that result from two closely related but separate species.

  Examples:

  - Mules are hybrids as they are the offspring of donkeys and horses. Mules have been deliberately bred by humans since ancient times, as they are larger and faster than horses, and also less picky around food than horses. Under the biological species concept, mules are not considered species as they are infertile and cannot reproduce with other mules.

  - Another example are pantherine, which are a subfamily of cats that include tigers, leopards, jaguars and tigers. In captivity, they may breed and produce fertile hybrids. For example, a tigon and a liger are both hybrids of lions and tigers, and are also both fertile. Under the biological species concept, this would assume the pantherine to be one single species. However, the pantherine can only breed fertile hybrids in captivity.
• How is variation across geographical ranges a limitation for the biological species concept?

  Species are often not discrete grouping, but are approximations. This is because there is a gradient of variation within species, often across geographical ranges.
• How are asexually reproducing organisms limitations for the biological species concept?

  As asexually reproducing organisms do not interbreed, the biological species concept is unapplicable to them.

  Therefore, asexually reproducing organisms are classified into species based on appearance or biochemical similarities.
• How are the practical challenges of testing a limitation for the biological species concept?

  To determine species via the biological species concept, natural breeding and the production of fertile offspring must be observed. However, this approach is often impractical in many ecosystems. For example:

  - Some organisms live in the bottom of the ocean and cannot be logistically or technically observed

  - There are ethical concerns regarding the observation of some organisms

  - Extinct organisms cannot be observed reproducing, so they are classified into species based upon morphology. However, this is difficult due to chrono species- different stages in the same evolving lineage that existed at different points in time without splitting or branching.
• How is geographical location a limitation for the biological species concept?

  Organisms may not interbreed simply due to physical separation, not because they're genetically different.
• How is divergence during speciation a limitation for the biological species concept?


  Speciation is the formation of new and distinct species in the course of evolution.

  Speciation is gradual, and often arises from the splitting of pre-existing species. Genetically diverging populations may be difficult to distinguish as distinct species, especially as there is a continuum from restricted gene flow between the ancestral species and the reproductive isolation of the two resulting species.
• What is the phylogenetic species concept based on?

  Based on genetic lineage and evolutionary history (DNA comparisons)
• What is the ecological species concept based on?

  Based on ecological niche and role in the environment
• What is speciation, and why is it difficult to distinguish two distinct species?

  - A population is a group of organisms of the same species that live in the same area at the same time. If they do not interbreed, then physical and behavioural differences may accumulate and they may diverge to the point of becoming different species. This process is known as speciation.

  - Speciation often occurs gradually. It is also difficult to distinguish when there are two different species, as genetically diverging populations may be hard to distinguish as unique species as the speciation process is occurring, because there is a continuum from merely somewhat restricted gene flow within the ancestral species and the reproductive isolation of the two resulting species.
• What are some examples of speciation?

  - Brown bears (Ursus arctos) and polar bears (Ursus martimus) are closely related species. Biologists estimate that polar bears and brown bears speciated between 1.3 and 1.6 million years ago. However, despite their speciation and distinct species, brown bears and polar bears still mate with each other. This is due to climate change allowing both populations to come back into contact with one another.

  - Some related species may also be difficult to distinguish from one another. Transient killer whales (Orcinus rectipinnus) and resident killer whales (Orcinus ater) have only recently been identified as separate species and not different population of the same species.
• What are chromosomes?


  Chromosomes are defined as threadlike structures of nucleic acids and histone proteins that carry genetic information in the form of genes. They are found in the nucleus of eukaryotic cells.

  Most organisms have chromosomes in pairs (homologous pairs) - one from each parent.
• What are diploid and haploid numbers, and what are some examples?

  - Each species has a characteristic number of chromosomes in its somatic (body) cells.

  - The diploid number is the number of chromosomes in a single somatic cell, and is 2n.

  - Diploid cells have an even number of chromosomes because chromosomes are in homologous pairs.

  - The haploid number, n, is half the diploid number, and is found in gametes.

  Examples:

  - Human diploid number- 46.

  - Human haploid number- 23

  - Chimpanzee diploid number- 48.

  - Chimpanzee haploid number- 24
• What is the suggested origin of human chromosome 2, and what is some evidence that supports this?

  Human chromosome 2 arose from a fusion of chimpanzee chromosomes 12 and 13. This explains why humans have 46 chromosomes, while other great apes have 48.

  Evidence to support this:

  - Branding pattern

  - Telomeres in the middle

  - Two centromeres

  - DNA similarity
• What is a karyotype?

  The number and characteristic type of chromosomes present in the nucleus of a cell.

  Characteristic of a species (e.g., humans = 46).
• What is a karyogram?

  A photograph or diagram of the chromosomes of an organism, arranged in pairs according to size and structure. (from largest to smallest)
• What are some uses of a karyogram?

  - Sex determination

  - Diagnosing disorders

  - Evolutionary comparison
• How are chromosomes identified?

  - Size - largest to smallest. In humans, chromosome 1 is more than 5x longer than chromosome 21.

  - Centromere position - metacentric, submetacentric, acrocentric.

  - Banding pattern - visible after staining. There is different banding in each type of chromosome.
• How are sexes deduced from a karyogram?

  Chromosome 23:

  XX → female.

  XY → male (Y chromosome is smaller and distinct).
• What is a genome?

  A genome is the complete set of genetic material in an organism, or the entire base sequence of each of the organism's chromosomes.

  All individuals in a species share most of their genome- Humans share ~99.9% of their DNA with each other.

  This ensures:

  - Similar body structures

  - Similar biochemical processes (e.g., enzymes, hormones)

  - Inherited traits typical of that species
• What is a gene?

  A gene is a length of DNA that contains a sequence that codes for a specific polypeptide (or functional RNA).
• What is an allele?

  An allele is a different version of a gene that occupies the same locus (position) on a chromosome and differs by one or a few bases. The difference lies in the base sequence.

  Alleles introduce diversity into the genomes of species.