A3.1 Diversity of Organisms

Species

Group of Organism that can interbreed and produce fertile offsprings

Why is horse and donkey not the same species

Horse(2N=64) and donkey (2N=62

= Mule (2N=63)

→ cannot carry out meiosis as chromosome cannot form homologous pair in metaphase I

→ Infertile

→ cannot produce fertile offspring

Clasify Organisms- Carl Linnaeus

1. Taxonomy

2. Based on the Morphological structure: Classifying organisms based on their physical appearance and structure

Taxonomy

→ classifying organsims into taxa (ordered group)

Kingdom → Phylum → Class → Order → Family → Genus → Species

Challenges to the biological species concept

Asexual Reproduction

Migration bringing different species together, who can interbreed

Species who look almost identical to each other

Divergent Speciation

• If two populations of the same species are separated in some way and are unable to interbreed

• They may diverge

• developing adaptations to their environment

• genetically becoming more different until they can be classified as two different species. 

Speciation:

splitting of one species into two or more species

Population

group of organisms of the same species living in same area at same time

Karygram and karyotype

A karyogram shows the chromosomes of an organism in homologous pairs, organised in decreasing length.
The karyotype is the number and types of chromosomes in a eukaryotic cell.

• technique used to observed chromosomes.

• It can be used to identify the

  • sex of the fetus

  • check for any chromosome abnormalities

  • compare chromosomes between species

Karygram and karyotype steps

1. Extract cells from sample organism

2. Cells are stained and prepared on a glass slide under light microscope

3. Allow cell to divide and pause at metaphase

4. Photomicrograph images are obtained

5. Arrange chromosome base on their size and structure

Karyotypes in a karyogram

• Banding patterns can be used to identify which chromosome it is and the pairing.

• Images of chromosomes are placed in order by size and position of their centromeres.

• Generally arranged in decreasing length, except chromosome 23

Compare Human and Chimpanzee Chromosome

Human - 46

Chimpanzee - 48

→ Two possible hypotheses:

1. Chromosome disappeared

2. 2 chromosome from chimp has fused

evidence for fusing of chromosome in chimpanzee and human

12&2

• When chromosome 12 and 13 are placed end to end, they have a similar length to the human chromosome 2

• Centromere of chromosome 2 line up with chromosome 12

• Band pattern in short arm for chromosome 2 matches chromosome 12

• Telomeric DNA are found in the middle of chromosome 2 and it correspond to the end position of chromosome 12

13&2

• Centromere of chromosome 13 corresponds to a non-coding part of human chromosome 2

• Band pattern in long arm for chromosome 2 matches chromosome 13

A genome contains

all the genetic information of an organism

Dichotomous Keys

tool to identify a species that is not recognised

Dichotomous keys can be represented as either

1. A branch diagram

2. A paired statement key

• The subjects are repeatedly sorted into 2 categories until they no longer share any further characteristics with each other.

Variations in Species - SNP

• Organisms in the same species share most of their genome but variations from SNPs (single-nucleotide polymorphisms) exist

• SNPs are classified as positions in the gene where at least 1% of the population have a different base.

• smaller than 1% of having different base → mutation

Unity and Diversity in same species

same:

• Number of chromosomes

• Position of the same genes in the same sequence on the chromosomes.

Different

• different versions of those genes (alleles) → base differences

Variation between species

• Variation in genome size. This is determined by the total amount of DNA, measured in base-pairs.

• Variation in base sequence. 

• Variation in number and types of genes

Uses of genome sequencing

Current

• investigate the evolutionary origins of species

• Research into the genomes of pathogens → help us control and prevent infectious diseases caused by these organisms.

Future

• understand the origins of human life, and migrations.

• every person’s genome can be sequenced to develop personalized medicines and treatments, as well as accurately predict future health problems.

Human genome project

• The goal is to sequence the nucleotide of varies gene

• There are 25000 genes present in the human genome.

Outcomes:

1. To determine the function of genes

2. Knowing the evolutionary relationship between human and other organism

3. Helps to classified a newly discovered organism

4. Allow development of genetic diagnosis

5. Allow development of genetic tailored-made drugs

why is bacteria not a species

due to horizontal gene transfer

• Not interbreeding→ not making a new bacteria, just sharing a copy of plasmid

• Not fertile offspring→ just another individual

DNA barcodes 

• short sequences of DNA, usually from only one gene, which are distinct enough to identify different species.

DNA barcode in identifying a organism

• unknwon speciman / environmental sample

• DNA extraction and amplification

• DNA sequencing , produce dna barcode

• sample compared to barcode database

• match found → species identified

Use of dna barcoding

1. distinguish between morphologically similar species

2. identify a specimen from a small or incomplete sample (e.g. leaf litter)

3. monitor biodiversity (simply through organism’s interaction with sampled environment)