Term 3 - A3.1 Diversity of organisms

A3.1.1 Variation (4)

• Variation is the differences in the characteristics of individuals in a population

• Is found in all living things - there is variations between same species, but more variation between diff species

• Due to genetics, environment, or combo

• No two individuals are identical in all their traits

A3.1.1 Genetics (1 + 2, 2)

• Genetics:

  • Diff members of population are diff DNA

  • Diff alleles (e.g. allele for blue eyes or allele for brown eyes)

• Genetic variations - some individuals are better adapted to their environment than others --> natural selection

• Examples: eye coloud, blood group

A3.1.2 Species (2 + 3 + 2)

• Definition: A species is a group of individuals that can interbreed that can produce fertile offspring and are reproductively isolated from other species

• Key points:

  • Can interbreed (can mate)

  • Can produce fertile offspring

  • Are reproductively isolated

    • Physically prevented from mating with other species

    • Genetically incompatible (e.g. different chromosome numbers)

A3.1.2 Two ways to determine species (2)

1. Old way - morphological species concept - looking at common structures - proposed by Carolus Linneaus

2. Newer way - biological species concept

A3.1.2 Carolus Linneaus (2)

• Taxonomy is the science of classifying organisms

• Carolus Linnaeus developed a classification system based on morphology (observable physical traits) of organisms

A3.1.2 Morphological Species Concept (1)

The morphological species concept defines species as groups of individuals which are morphologically similar (similar traits) to each other, and morphologically different from other species

A3.1.3 Binomial Nomenclature (2)

• All organisms are given a scientific name according to Linneaus's system of binomial nomenclature

• Are typed in italics and written with an underline; capital first letter of first word and all lowercase for second; genus then species

• When writing scientific name on paper, underline

• Genus species

A3.1.4 Biological Species Concept (2)

• A species is a group of organisms capable of reproducing with each other to produce fertile offspring

• Organisms may have similar characteristics, but if they are not capable of reproducing with each other, they are considered to be different species

A3.1.5 Speciation (3)

• The process of giving rise to a new species; is the splitting of one species into two or more species

• If a population of a species becomes reproductively isolated into two separate populations (groups are unable to meet and reproduce), they may gradually evolve into separate species, as the different populations evolve different traits over time

• It is an arbitrary decision, whether two populations are regarded as the same or different species, since they do not meet to reproduce in nature

A3.1.5 Population (1)

Population: A group of organisms of the same species, living in the same area, at the same time - members of the population can interbreed

A3.1.6 Diploid Chromosome Number in Eukaryotes (2)

• Diploid eukaryotic cells will have two complete sets of chromosomes in their nucleus, resulting in an even number of chromosomes in each cell

• There is great diversity in the number of chromosomes found in cells of different species

A3.1.7 Karyotype (3)

• A karyotype is the number and type of chromosomes found in a cell

• Humans have 22 pairs of autosomes, and 2 sex chromosomes (46 chromosomes in total)

• Visualised with a karyogram

A3.1.7 Karyogram (3)

• A karyogram is a diagram or a photo of the chromosomes found in a cell

• In a karyogram, chromosomes are organised into homologous pairs of chromosomes

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

A3.1.7 Karyogram Steps (1 + 3, 1 + 3)

• Steps:

  1. Stain cells

  2. Break cells to release chromosomes

  3. Photograph & rearrange chromosomes

• Chromosomes are arranged based on:

  1. Length

  2. Centromere position

  3. Bending patterns

A3.1.7 Origin of Human Chromosome 2 (2)

• Chimpanzees are humans’ closest relative, however chimpanzees (and other members of our taxonomic family such as gorillas and orangutans) have 24 pairs of chromosomes, but humans have 23 pairs of chromosomes

• 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

A3.1.7 Evidence for the Origin of Chromosome 2 (4)

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

• A vestigial telomere is found within human Chromosome 2, suggesting the fusion site for Chromosome 2A and 2B

• The sequence of genes on human Chromosome 2 matches the sequence of genes on the chimpanzee Chromosomes 2A and 2B

• The banding pattern formed when human Chromosome 2 is dyed matches the banding pattern on the chimpanzee Chromosomes 2A and 2B

A3.1.8 Genome & Gene (2)

Genome: all the genetic information of one organism, contains both coding and noncoding regions

Gene: the basic physical and functional unit of heredity

A3.1.8 Unity & Diversity (1 + 2, 1)

• Unity: Organisms within the same species have the same genes in the same position on their chromosomes

  • Similar chromosome length, shape, banding

  • ~99% of genome will be similar

• Diversity: the 1% of difference between individuals of the same species due to the presence of SNPs

A3.1.8 Polymorphisms (3)

• Polymorphisms refers to the existence of multiple forms of a particular trait or characteristic within a species

• Polymorphisms can result from single-nucleotide base substitution mutations

• Organisms in the same species share most of their genome, but variation exists in the form of single-nucleotide polymorphisms

A3.1.9 Diversity of Eukaryotic Genomes (3 + 3)

• Genome size is the total amount of DNA in a cell

• Genome size is measured by the number of nitrogen base pairs (BP) which form the two strands of DNA (NOT weight of DNA as it is too light)

• Usually genome sizes are measured in:

  • Kilobases (1kb = 1000bp)

  • Megabases (1Mbp = 10⁶bp)

  • Gigabases (1Gbp = 10⁹bp)

A3.1.9 Human Genome (2 + 3)

• 1.2% of the genome codes for protein --> coding regions

• 98-99% --> non-coding (not responsible for protein production)

  • 50% junk DNA (transposons) - function unclear

  • Regulatory elements - promoters that help to start transcription

  • Structural elements - telomeres (found at the end of chromises to protect the DNA sequence) & centromeres

A3.1.9 Complexity of Organisms (5)

• Variations in the number of chromosomes, genome size, and number of genes are greater between different species and don't predict the complexity of an organism

• However, organisms of the same species should have the same number of chromosomes, genome size, and number of genes

• Only variation between members of the same species --> SNPs

• The nucleotide base sequence of a genome varies between all individuals

• However, nucleotide base sequence variation between individuals from different species is much greater than for individuals from the same species

A3.1.9 Cyc1 Gene (4)

• Produces the cytochrome c protein (cyc1 protein)

• Responsible for cellular respiration and apoptosis

• Highly reserved within living things because it is important for general functioning of cells

• All four organisms should come from the same common ancestor

A3.1.10 Genome and Size Complexity (1)

• There is a clear increase in genome size and complexity from viruses → prokaryotes/bacteria → eukaryotes

• 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, as seen in the graph

 

A3.1.11 Genome Sequencing (2)

• Genome sequencing determines the entire genetic makeup of an organism

• Improving technology is reducing the cost and time of sequencing genomes

A3.1.11 Genome Sequencing and Evolution (1)

• Scientists have sequenced the genomes of thousands of organisms

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

A3.1.11 Genome Sequencing and Personalised Medicine (1)

Personalized medicine takes into account an individual’s genetic makeup to provide targeted and effective medical treatment

A3.1.11 Benefits of Personalised Medicine (3)

1. Diagnosis and treatment of genetic diseases though the identification of genetic mutations. The focus of treatment can shift from prevention rather than reaction to illness

2. Prescribe more effective drugs, with fewer side-effects, based on a person's genome

3. Reduces trial and error prescription of medicines, through identifying more targeted medications

A3.1.11 Genome Sequencing - Applications (1 + 1, 1)

• Fighting diseases:

  • Sequence the genome of patient and compare to the genome of healthy individuals --> find out what is the underlying cause of disease --> personalised medicine/targeted therapies -->

• Establish evolutionary relationships between different species --> cladograms