Study of biological diversity in an environmental context, encompassing taxonomy,
involving reconstruction of phylogenetic history/ study of organisms and their
evolutionary relationships is Systematics.
Taxonomy is branch of Bio that names/classifies forms of life
Phylogeny refers to the evolutionary history of a species/group of related species.
(a) Explain binomial nomenclature of a species and hierarchical classification.
- 2 part latinised name
- 1st part – genus (genera pl.)
- 2nd part – species within the genus
(b) Describe the classification of species into taxonomic groups and appreciate
significance of various concepts of the species.
Kingdom Phylum Class Over Family Genus Species
(c) Explain relationship between classification and phylogeny
- Linnaean scheme is classification based on presumed homologies (anatomical
features of similar function or appearance because they were inherited from
common ancestor. The more homologies shared, the closer in evolutionary
distance.) Goal of systematics is to determine phylogeny, by constructing
phylogenetic trees representing hypothesized evolutionary relationships between
organisms. To do that, we must have data from classification.
(d) Explain why variation is important in selection
- Selection is based on heritable variation. When environmental changes occur,
variation allows some individuals to survive better, reproduce more successfully
to produce Fertile Offspring. This ensures perpetuation of species and safeguards
species from extinction.
(e) Explain with e.g. how environmental factors act as forces of natural selection.
Case study of peppered moth during Industrial Revolution. Melanic moths in
polluted areas can better camouflage with blackened tree trunks where they rested
during the day. Light-colored moths in distant forests were present in higher
frequencies.
(f) Explain how natural selection may bring about evolution
Natural selection refers to the differential success in reproduction of different
phenotypes resulting from interaction of organisms with their environment.
Because
Species produce large number of offspring, but only a constant fraction of the
offspring population will survive, mature and reproduce at reproductive age. This
is because there is a struggle for survival and reproduction due to competition for
limited resources (selection pressures). In a population, variation exists. Natural
selection works upon variation, identifying those better adapted to environment.
Because of selection pressures, there is the survival of the fittest (relative ability
of individuals to produce fertile, viable offspring) to reproduce ( reach
reproductive age to produce fertile, viable offspring), to pass on inheritable
selective and reproductive advantages.
Therefore
Overtime, the unequal ability of individuals to survive and reproduce leads to
gradual change in population= evolution. Certain favorable/advantageous
characteristics/genotypes accumulate.
(g) Explain why population is smallest unit that can evolve.
“Population” – Group of interbreeding individuals belonging to particular species,
sharing common geographic area.
“Evolution” – change in allele freq./ mutation, gene flow, genetic drift, random
mating, natural selection.
-
Evolution is the collective genetic response of a population – determining
survival or formation of species.
long term effects of natural selection are at gene level of population because
members interbreed and exchange inheritable genes
Evolution is measured as changes in relative proportions of heritable
variations in successive generations of a population.
(h) Explain how homology (anatomical, embryological and molecular) supports
Darwin’s theory of natural selection.
“Homology” is the similarity in characteristics resulting from shared ancestry
even though they may have different functions. E.g. Flipper of dolphin, forelimb
of human
“Analogy” structures with similar functions but based on vastly different
structures, and organisms do not share common ancestry. E.g. Fish fin and
dolphin flipper
Anatomical homology sharing common ancestry in aspect of morphology in
form and structure
Embryological homology common ancestry based on similarity of
developmental pathways (anatomical characteristics in embryos)
e.g. (comparative embryology) 1. all vertebrate embryos have gill pouches on
sides of throat. 30-ady old human embryo has pharyngeal gill pouches like
developing fish. 2. vertebrate embryos have a notochord and yet is the only
primitive protochordates that retain this structure in adult. Early in development,
human embryos have notochord that becomes greatly reduced, giving rise to discs
between adult vertebrae. 3. Visceral clefts become auditory canal and tube for
mammals.
Molecular homology common ancestry in molecular (DNA, Amino Acid
Sequences) makeup of related species
- it is consistent with other evidence in testifying that evolution is a remodeling
process in which ancestral structures that functioned in one capacity becomes
modified as they take on new functions.
(i) Explain how biogeography and fossil record support evolutionary deductions
based on homologies.
Biogeography – study of past and present distribution of indiv species/ entire
communities. E.g. Island Biogeography & Sugar gliders vs. Flying squirrels
1) many species are endemic to islands. Most island species closely related to
species from neighbouring islands. “Island Hopping” is the rise of new
species when populations spread out.
2) Species tend to be closely related to other species from same area than to
others with same way of life in other areas. Sugar gliders (aus), flying
squirrels (north america) are species with similar characteristics due to
environmental factors but are not closely related. (Convergent Evolution/
Analogy)
3) By studying distribution of organisms/how they disperse, this determines
if they are homologous and traces evolutionary pathway.
E.g. Continental Drift, Wallace Line and Lungfish Distribution
4) Lungfish believed to be closest living relatives of tertrapods. Each specie
found in different continent – continents connected in the past.
Fossil Records – support evolution by showing sucession of organisms shown within
layers. Deeper stratum – older organism, transitional forms. Also show
depopulation/immigrations/mass extinctions. BUT are often incomplete.
(j) State advantages of molecular (nucleotide and amino acid sequences) methods in
classifying organisms.
Species diverge as changes occur in nucleotide bases, with each specie acquiring
their own genetic mutations – can predict that species that are phylogenetically
closely-related have more simlar nucleotide sequences in nucleic acids/amino acid
sequences.
1. Objective, detailed, unambiguous and quantitative. Distant phylogenies share
few morphological similarities.
2. electronic databases for comparative study/classification
3. limits set of characters studied
4. Nuclei acids common characteristics of all known life.
5. Generated quickly in single experiment.
(k) Explain how genetic variation e.g. recessive alleles may be presented in a natural
population
(1) Diploidy – Heterozygote protection
A gene can be dominant/recessive. Dominant alleles mask or hide
recessive alleles so recessive trait requires 2 recessive alleles, one/parent.
Recessive Alleles are less favourable in current environment. BUT they persist
because they are propagated in heterozygous individuals.
(2) Heterozygote advantage
E.g. Sickle Cell Anaemia Homozygous recessive individuals usually die,
eliminating 2 recessive alleles from population. Possessing a single sickle cell recessive
allele have increased resistance to malaria.
E.g. Cystic Fibrosis – autosomal recessive hereditary disease of
lungs/sweat glands/digestive system. Heterozygote advantage is increased survivorship of
disease involving fluid loss, e.g. diarrhea.
(3) Inbreeding
Low chances of inheriting recessive allele for genetic disorder because of
high genetic diversity. But inbreeding increases chances of both parents having recessive
allele.
(l) Briefly describe the neutral theory of molecular evolution.
Molecular clock – constant rate of evolution of alpha-globin is e.g. of ‘clocklike’
evolution of genes and proteins. Amount of molecular change between 2 species
ensures how long ago they diverged into 2 different species from a common
ancestor. = Molecular evolution is constant enough to provide clock for evol.
Neutral Theory contends that much evolutionary change at the molecular level
of genes and proteins are selectively neutral (no effect on fitness) and is driven by
genetic drift rather than natural selection.
Genetic drift reduces genetic variation in populations, potentially reducing a
population’s ability to evolve in response to new selective pressures. Genetic
drifts are greater in smaller populations, important effect for endangered species.
Genetic drift also contributes to speciation, having small isolated population
diverge from larger population.
So. Not all allele frequency changes are a result of natural selection. It is often
Explained by the Neutral Theory, a neutral selection outcome that does not affect
and organism’s fitness