artificial selection Flashcards
artificial selection
-This example was used by Darwin in the origin of species
-Variation in species generated by human-driven selection
-Breeding and producing viable offspring
-Selecting on morphology
examples of animals that have been artificially selected
-pigeons: variations and selection of different characteristics and many years of breeding
-dogs: wolfs are the domestic dog ancestor
-crops: eichorn (small feeds) -> heritage wheat (beginning of 19th century, huge grain, lots an hour produced)-> modern wheat
-Ancestral crops were selected for desirable characteristics – these have been amplified through artificial selection
crops and artificial selection
-good evidence of evolution
-change using selective breeding
Has artificial selection generated a new species
-New species that is a hybrid between two existing ones.
-Parental species are Primula verticilliata and Primula floribunda
-Speciation through allopolyploidy: the hybrid of the two parent species has doubled chromosome number
-E.g. Primula kewensis – 2n=36; in both parents, 2n=18
-Leads to ‘instant speciation’
-More common than you might think in nature: 40-70% of plant species are polyploids
reasons for Darwin using the example of origins of species
-Species are not immutable – change is possible
-Accumulation of small changes
-Directional change through selection
changes in foxes due to climate
-Alaska in the north and California in the south.
-There are clear changes occurring: foxes are larger in the north; they have thicker fur, smaller ears, thicker limbs; on the other hand, further south thy have thinner fur, larger ears, thinner limbs and are smaller
-Lepus californicus = Black-tailed jackrabbit
-Similar trends in hares – arctic hare versus black-tailed jackrabbit.
-Herring Gull: light colour mantle
-Lesser black-backed Gull: darker wings
-have behavioural differences
what are Biogeographical ‘rules’
-Bergmann’s rule: animals get larger further north
-Allen’s rule: animals in colder climates have thicker limbs
Lack’s rule: the clutch size of each species has evolved to an evolutionary optimum
-Rensch’s rule: sexual dimorphism increases with average body size
-These ‘rules’ don’t always work, and have been controversial at times: however they tell us that there are common adaptive responses of organisms in different places
sparrow changes in space
-Italian sparrow occurs in an area of overlap of House and Spanish sparrows
-Almost certainly arose as a hybrid between them
-Now a distinct species (i.e. independent breeding populations)
fossil evidence
-Fossils are contained within layers of sedimentary rock
-Older layers covered by new ones
-Can trace inter-relationships and transitionary forms
-Also preserved animals – e.g. in permafrost
the evolution of horses
-hooves have evolved to run faster
-fossils of teeth and legs were traced back
what do transitional forms int the fossil record demonstrate
-the evolutionary links between major groups
what are homologous characters
-Homologous characters are traits that are inherited from a common ancestor
-Although they are inherited, they may now serve different functions
-The existence of homology shows that different groups have evolved from common ancestors
-As well as show where they have diverged
bats and homology
-The limbs of bats and birds are homologous as they inherited these from a common ancestor
-They each have 2 pairs of limbs – ‘arms’ and ‘legs’
-However the differences in structure mean that at the same time their wings are non-homologous (analogous)
-The forelimbs of birds bats and humans show homology – they are comprised of the same bones
-But the wings of bats and birds are structurally very different: they are therefore not homologous
-all organisms developed bones from common ancestors
what are vestigial characters
-Extant organisms have structures that serve no function
-Their presence serves as evidence of evolutionary relationships
-Also, provides evidence of evolutionary change
-Eyes of organisms such as cave-dwelling fish have become vestigial showing evolutionary change in response to environmental selection
-Whales possess pelvis bones,
linking them to terrestrial mammals
whats experimental evolution
-Using fast-reproducing organisms, it is possible to demonstrate evolution under lab conditions
-e.g. until Covid-19 Richard Lenski and colleagues had been able to proliferate E. coli for 73 500 generations [Note there have only been about ~7500 generations of humans]
-There were 12 founding populations and all of these showed the same evolutionary response to the conditions
-Experimentally imposed stresses lead to evolutionary changes that can be measured
-Can test evolutionary theories
