diversity of organisms A3.1

Variation between organisms

• no 2 organisms are completely identical in all their traits.

• The patterns of variation are complex and are the basis for naming and classifying organisms.​

morphological concept

describes species based on their observable features

advantages of the morphological concept

• can be applied to both sexual + asexual organisms

• does not require any information on the extent of gene flow

• can be applied to extinct + fossilised species

disadvantages of the morphological concept

• subjective

• different individuals of the same species can look very different.

• individuals of different species can look similar

Binomial system for naming organisms

• groups organisms to represent similarities and proposed relationships. (based on physical traits)

• consists of 2 names :

• Genus (begins uppercase)

• Species (begins lowercase)

• e.g Homosapiens

smallest group in binomial system

• subspecies (3rd name)

• can potentially interbreed if a barrier/challenge were to be removed

species according to biological species concept

a group of organisms that can breed and produce fertile offspring. (in reproductive isolation)

advantages of biological concept

• not subjective

• practical

• Clear reproductive criterion – focuses on whether populations can interbreed, which directly links to reproductive isolation and speciation.

disadvantages of biological concept

• doesn’t apply to organisms that reproduce asexually

• doesn’t apply to extinct organisms

• over emphasises gene flow and downplays natural selection - natural selection can cause many pairs of species which are morphologically and ecologically distinct to remain distinct and yet have gene flow between them

how is reproductive isolation ensured?

• Geographical isolation - populations are physically separated by barriers

• Behavioural isolation - differences in courtship behaviours prevent mating

• Temporal isolation - populations reproduce at different times during the day/season/year

what can lead to a barrier of reproductive isolation being removed?

• climate change - Shifts in temperature, rainfall, or seasonality can cause species to breed at the same time/place again.

• human activity - Deforestation, urbanisation, agriculture, and habitat modification

• geographical barriers removed - (Mountains erode, rivers dry up, land bridges form, zoos)

open vs closed populations

• open - population can migrate in or out. Allows more gene flow between populations. → less distinct features develop. ​

• closed - population with no migration. → little genetic mixing → different selection pressures to act.

speciation definition

• The gradual splitting of one species into 2 or more. 

• Becomes an arbitrary decision whether 2 populations are regarded as the same or different species. 

Homologous chromosomes definition

a pair of chromosomes that carry the same information. (can be some variety in info)

what are chromosomes made from

• DNA wrapped around a protein

• 1 chromosomes = 2 identical strands of DNA

number of chromosomes in humans + chimpanzees

• humans - 46

• chimpanzees - 48

diploid vs haploid cells

• diploid - even

• haploid - half

• e.g 46 and 23

what is chromosome number not an indicator of

how complex an organism is

what affects whether 2 animals can interbreed

• number of chromosomes

• position of genes on the chromosomes

how did chromosome 2 arise in humans

arose from the fusion of chromosomes 12 and 13 in a shared ancestor

• maybe chimpanzee ?

what is Karyogram

• an image where chromosomes are organised in their homologous pairs.

• according to size from the biggest to the smallest.

• Sex chromosomes are shown last.

karyotype definition

• the total number and types of all chromosomes in the nucleus of a cell during the early stage of nuclear division (mitosis)

• Each chromosome is present as two

  chromatids, held together by its centromere.​

features used to identify chromosomes

• 1. size

• 2. banding pattern

• 3. centromere position

genome definition

all the genetic information of an organism

human genome is made from 23 pairs of chromosomes

where is the genome found in a cell

mostly in cells nucleus but also a small amount is in mitochondria

how is genome size measured

• base pairs (bp)

• determined by total amount of DNA

• isn’t necessarily caused by number of chromosomes as chromosomes can have different lengths

diversity of eukaryotic genomes

• genome size within a species is usually the same

• Variation between members of the same species are caused by changes in the base sequence of the DNA.​

• genome size between different species varies in number of chromosomes + total amount of genetic material(genome).

what is diversity in genome of the same species caused by?

• SNP’s Single nucleotide polymorphisms

• variation in individual genes - alleles

• gene usually differs only by a few bases.

alleles

• alternative forms of a gene

• Alleles are caused by different changes occurring to the DNA, such as deletions, additions, insertions.​

Single nucleotide polymorphisms (SNPs).​

alleles in which only one nucleotide within the sequence differs → causes variation in genome of the same species

variation between species vs within a species

variation between species is much larger than variation within a species

relationship between genome size and organism complexity

genome size is not an indicator of organism complexity

why use genome sequencing

increasing speed and decreasing costs

current uses of genome sequencing

research into evolutionary relationships - when looking at whole genomes

future uses of genome sequencing

personalised medicine → a medical approach that tailors disease prevention, diagnosis and treatment to individual patients based on their unique genetic makeup, lifestyle + environment

• e.g cancer treatment → developing therapies based on the unique genetic makeup of a patients tumor to target it more effectivly