A3.1 Diversity of Organisms

Variation between populations of organisms is the basis for naming and classifying organisms. It is the difference In traits between individuals, no two individuals are identical in all traits.

Taxonomy- Linnaeus

The science of classifying organisms

Morphology- developed by Linnaeus, a classification system based on observable physical traits

  • Morphological Species Concept

    • defines species as groups based on morphological similarities and differences.

Binomial Nomenclature- scientific names are written in italics or underlined

Part one- Genus and begins with an uppercase letter

all members of a genus share similar traits

Part Two- species name and begins with a lowercase

ie- Homo sapiens

Biological Species Concept- a group of organisms capable of reproducing with each other to produce other fertile offspring.

  • replaced morphological species concept

Population- group of the same species, same place, same time

Speciation- the splitting of one species into 2+ species.

Diploid number of cells- differs by species

Humans- 46

Chimpanzees- 48

Dogs- 78

Karyotypes and Karyogras

  • Karyotype- the number and type of chromosomes found in a cell

  • Karyogram- diagram or photo of chromosomes found in a cell.

  • Homologous chromosomes- have the same sequence of genes and are the same length.

Males- X and Y chromosomes

Females- X and X chromosomes

Trisomy 18- Edwards syndrome- body development and growth (low birth weight, birth defects etc,)

Trisomy 13- Patau Syndrome intellectual disability and physical abnormalities

Origin of Human Chromosome 2

Chimps and humans are closely related, they have 24 pairs of chromosomes and we have 23.

The working hypothesis is that two ancestral chromosomes fused to form chromosome 2 in human ancestors after they had diverged from our common ancestor with chimpanzees.

Evidence

  • Chromosome 2 is the same length as Chromosome 2A and 2B in chimpanzees.

  • vestigial telomere suggest the fusion site for Chromosome 2A and 2B

  • Sequence of genes on human C2 matches the chimp gene sequence in 2A and 2B

  • banding pattern formed when human 2 is dyed matches the banding patter of chim 2A and 2B

Genome- includes all the genetic information of an organism needed for growth and development of cells.

Polymorphism- the existence of multiple forms of a particular trait or characteristics within a species.

  • can result from single-nucleotide base substitution mutations

Genome Size- total amount of DNA, measured in nitrogen base pairs (bp) which form the bonds between the two DNA strands. -

  • Kilobases (1kb = 1000bp) 

  • Megabases (1Mb = 1,000,000bp).

  • Gigabases (1Gb = 1,000,000,000bp)

Prokaryotes are more complex than viruses, and  require more genetic information.

Eukaryotic organisms require more genetic information than prokaryotes.

However, there is a wide range of genome sizes for eukaryotes,

Genome Sequence- determines the entire genetic makeup of an organism.

  • By analyzing the evolutionary relationships between species and the corresponding differences in their DNA, scientists can better understand how the appearance, behavior and biology of living things have changed over time

HL Content

Flaws of the Biological Species Concept

  • Asexual Reproduction: Some organisms can only produce asexually and cannot be defined as species.

  • Horizontal Gene Transfer- Transfer of genes between unrelated species is common amongst bacteria. It does not involved sexual reproduction but can lead to a new species.

Cross-breeding between closely related species is extremely unlikely if the chromosome number of the two species is not the same, as the chromosomes line up in homologous pairs during meiosis.

DNA barcode- a DNA sequence that uniquely identifies each species of living organism. It can be added and compared in a reference library, aiding species identification