A3.1 - Diversity of Organisms

Variation

A defining feature of life.

No two individuals have all the same traits. The pattern of variation is complex and it it the basis of naming and classifying organisms.

Morphological species concept

Species = a group of organism that have shared traits, share particular outer form or inner structure

Doesn’t take account into Charles Darwin’s evolutionary theory

Binomial system

Genus + species

Species in the same genus have shared traits

Biological species concept

Species = a group of organism that can breed and produce fertile offspring.

Difficulties of biological species concept

Difficult to apply for some organisms due to geographical separation and gradual divergence.

Further difficulties when migration brings two closely related species together but apparently distinguished species

Speciation

Splitting of a species into two or more.

Two populations of a species do not interbreed and diverge. Recognizable physical differences may develop as the population becomes genetically more different. Differences continue to accumulate and two population eventually become separate species.

It is an arbitary/difficult decision whether two population are regarded as the same or different species.

Diversity in chromosome numbers

Humans have 46 chromosomes while chimpanzees have 48. This number can change during evolution. Decrease if they fuse together, increase if they split apart.

Diploid cells have an even number of chromosomes due to fusion of male and female gametes

Genome

All the genetic information of an organism, contains functional units called genes.

Unity of genomes

Diversity in genomes

SNP = Position in a gene where more than one base pair is present. Main factor in making humans different from each other.

Diversity of eukaryote genome

Genome size vary in different species, which is determined by the total amount of DNA.

Genome size is measured in base pairs

Populations have difference in base sequence - if populations start to diverge to form separate species, differences will accumulate.

Diversity in eukaryote genome 2

Different species have different types and numbers of genes. Genes can be removed or added to a genome.

Species that developed from a common ancestor developed differences. Variation between species is much larger than variation within species.

Genome sequencing

Technological development both increased the speed of sequencing and reduced the cost.

Genome sequencing current use

• Easier to conserve and protect biodiversity

• Increased understanding of human origins and migrations in all parts of the world.

• Provide more data about genetic diseases and genes that affect human health.

• Identify evolutionary relationships between species

Genome sequencing future use

May be possible to sequence the genome of every person which could lead to the development of personalized medicine.

Difficulties of applying biological species concept

Do not work with organisms that does not sexually reproduce or transfer genes.

Difficulties of applying biological species concept - asexually reproducing organisms

If a clone does not interbreed with a clone, it is a separate species according to the BSC.

Example includes dandelions. Sexually reproducing organisms are a unified group.

Difficulties of applying biological species concept - horizontal gene transfer

There is so much gene transfer in bacteria that it is debated whether BSC should be applied. Genes are transferred among distinct species of bacteria.

Cross breeding - chromosome number

Cross-breeding between closely related species is unlikely to produce fertile offspring if parent chromosome numbers are different.

If two organisms with different numbers of chromosome mated, meiosis is unlikely to occur as some chromosomes will not pair up.

DNA barcode/DNA barcoding

Short sections of DNA from one gene or several genes, which are distinctive enough to identify a species.

Can be carried out from DNA collected from abiotic environment