Biodiversity and Evolution Part 2

Biodiversity and Evolution Part 2

1. Species

   • A Species: A group of organisms with similar characteristics that can interbreed to produce fertile offspring
   • Two organisms can interbreed to produce hybrids
     • If the hybrids are fertile then the two organisms are in the same species (but may be different varieties)
     • If the hybrids are infertile then the two organisms are from separate species
       • The hybrids are infertile as they have an odd number of chromosomes, so their cells cannot perform meiosis as the chromosomes cannot pair up. So no gametes can be made

2. Binomial System

   • All organisms have two scientific names
     • The first name is the genus that the species belongs to
       • The second name is the species name

3. Biodiversity

   • Biodiversity: A measure of the number and variety of organisms found within a specified region
   • Varies depending on where you are on earth
     • The number of species per square kilometre increases as one moves from the poles to the equator.
     • Rainforests and coral reefs are the most diverse habitats on earth, they have the greatest number of species per square kilometre compared to anywhere else.
   • Extinction: The loss of species
     • Rate increased by: Loss of habitat, Over hunting, Competition from introduced species, New diseases, Drainage of wet lands, Pollution.
   • Varies over time
     • There has aways been extinction throughout history.
     • Humans have accelerated the rate of extinction during the last 200 years.
       • Due to negative impact on the enrolment which in turn effects the survival of organisms
   • The Simpsons diversity index is a calculation that can be done to asses the number of species in an area and the number of individuals of each species
     • The bigger the number the larger the biodiversity
       • Values are between 1 and 0
     • Low diversity index
       • Indicates harsh enviroments
       • There may be a lot of organisms but few species
       • There may be a lot of species but few organisms (Rare)
     • High diversity index
       • Less hostile environments
       • Wide range of niches and habitats available
       • More feeding relationships so more competition (may decrease biodiversity a little)
       • Something impacting one species is less likely to effect the numbers of another
         • Ecosystem is more stable

4. Polymorphism

   • An organisms appearance (phenotype) is determined by the genes in its genome (DNA)
     • An allele: A form of a gene
       • Two different alleles are heterozygous
       • Two of the same alleles are homozygous
     • When a species is being considered all of the alleles in a population are referred to as the gene pool
   • If a gene has more than one alley it is referred to as polymorphic
     • Arise from mutations which are passed on to offspring
   • The position of a gene on a chromosome is known as a locus (plural loci)
     • Polymorphic loci are an indicator of the genetic variation in a population
       • A high proportion of heterozygous individuals for lots of genes in a population mean that there is a lot of variation
         • Reduced polymorphism
           • E.g. the cheetah
             • In the past Cheetahs have experienced period where the population was drastically decreased. In a small population allele frequencies can increase or decrease by chance
               • Not al members of the population will become parents, so there alleles won't be passed on.
               • Not all parents produce the same number of offspring (genetic drift)
               • Many tests show no polymorphism between individuals
           • This is dangerous as one disease could wipe out the whole population

5. DNA fingerprinting

   • The sequences of bases of DNA can be used to asses the variation within a population
   • Molecular studies of DNA are helping taxonomists to asses relatedness of evolution of species and to overcome classification problems caused by convergent evolution.
     • DNA fingerprinting produces bands which can be used to compare base sequences.
       • The DNA is cut into fragments using restriction endonucleases (enzymes)
         • The fragments are then separated by gel electrophoresis.
           • The DNA is pul in a gel matrix and a current is applied, the DNA moves towards the cathode (as they are negatively charged). Smaller fragments move further than larger ones.
             • The DNA is then stained and photographed, the bands can then be compared.
   • conservationist use this information to help in captive breeding programmes
     • It can also be used to decide which species are endangered

6. Evolution

   • Evolution: The process by which new species are formed from pre-existing ones over very long periods of time
   • Darwins Observations
     • Observation 1
       • Individuals have a large number of offspring but adult population remains the same from one generation to the next
       • Conclusion 1
         • There is a struggle for survival between individuals in a population because there is competition for limited resources
     • Observation 2
       • Variation exists between individuals in a population
       • Conclusion 2
         • Individuals with beneficial or a selective advantage are more likely to survive and reproduce
           • These individuals with beneficial characteristics onto their offspring . This will repeat generation after generation.
   • Selection pressures: Enviromental factors that keep populations relatively stable.
     • These include: Disease, Predation and competition for resources

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