A3.1 Diversity of organisms

3 points about genetic variation

• exists across all organisms

• there is least genetic variation between genetically identical individuals

• essential for natural selection

genetic variation in monozygotic human twins

• embryo divides into two individuals

• start off with the same genes

• acquire different variations by mutations (different environment)

morphology

outer form and inner structure of typical members of a species

morphological concept/definition of species

• group of organisms sharing a particular outer form and inner structure

• organisms are unchanging

binomial naming system for naming species

• universal system

• avoids confusion from different local names existing for a species

genus

group of species that have similar traits

naming format for species

• [genus][species']

• genus name starts with UPPERCASE letter

• species name starts with LOWERCASE letter

• typed → italics

definition of species

group of organisms that can successfully interbreed and produce fertile offspring

challenge of the definition of species

• aesexual organisms might not be classified as species

• fertile hybridisation of two species might not be classified as species

  • e.g. female hybrids of tigers and lions

definition of population

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

speciation definition

gradual process where species diverge to form new species

• 2 populations living in different areas → no interbreeding → genetic variations → become 2 species

how is the number of chromosomes a characteristic feature of members of a species

• varies across species

• each species have a diploid number for chromosome number → even number

  • result of sexual reproduction - fusion of 2 haploid gametes

karyotype

number and type of chromosomes present in a cell or organism

karogram

photograph in which an organism’s chromosomes are shown in homologous pairs of decreasing length

preparation of karogram

• examine cells in metaphase

• photograph cell with no overlapping of chromosomes

• process photograph, classify chromosomes into homologous pairs

  • stains used to give chromosomes distinctive banding patterns

  • chromosomes vary in size → can classify easily

  • position of centromere is fixed for each chromosome type

evidence that humans and chimpanzees share recent common ancestor

hypothesis: ancestors used to have 48 chromosomes, 2 of them fused → 46 chromosomes only in humans

evidence:

• banding pattern of human chromosome 2 = very similar to banding of chromosome 12 and 13 in chimpanzees

• central region of human chromosome 2 has structure similar to telomere + extra vestigial centromere

  • chromosomes normally have 1 telomere at each end and one centromere

genome

all the genetic information of one individual organism / group of organisms

gene

a length of DNA carrying a sequence of bases

genome showing unity

members of a species carry the same genes along the same chromosome → no genes are lost/duplicated during meiosis while promoting genetic diversity

genome showing diversity

• different alleles (variations in genes)

  • Single nucleotide polymorphism: positions in a gene where more than one base may be present

    • found in more than 1% of population

diversity in eukaryotic genome

• variation in genome size

  • addition or removal of genes from chromosomes

  • duplication or deletion of chromosome sections

  • increase or decrease in chromosome number

• variation in base sequence

  • can lead to speciation

  • some genes have very few variations in base sequence because they serve vital functions

how is knowledge of genome sizes useful

estimate cost and difficulty of future genome sequencing programmes

gives information about genome evolution

whole genome sequencing

determining the entire base sequence of an organism’s DNA

• comparisons between genomes → reveal relationships between species and evolutionary origins from common ancestors

future uses of whole genome sequencing

• sequencing genome for everyone → personalised medicine

  • SNP and genetic features of a person’s genome is known → predict health problems

difficulties with the definition of species with aesexual species

organisms that only reproduce asexually are genetically identical to parents

• no interbreeding with one another → each clone is a separate species

• mutations → clones splitting → increasing number of different clones

example of aesexual species

blackberry

• many blackberry clones are named as separate species

• a better policy is to consider organisms that abandon sexual reproduction to no longer be species

horizontal gene transfer

genes transferred from one species to another; vertical gene transfer: genes transferred from parents to offspring

• horizontal gene transfer is frequent among bacteria and prokaryotes, less frequent in eukaryotes

  • antibiotic resistance genes move from one species to another

DNA barcodes

short sections of DNA from a gene / several genes which are distinctive enough to identify species

• allows scientists to identify species from small pieces of tissue that may otherwise be difficult to recognise

• allows scientisits to identify organisms that have interacted with the sampled environment → investigation of biodiversity of habitats