topic 5 Flashcards
when does evolution occur?
when heritable characteristics of a species change
what is the mechanism of evolution?
natural selection
give 5 pieces of evidence for evolution
- fossil record
- selective breeding of domesticated animals
- homologous structures
- speciation
- patterns of variation
fossil record
- many sequences of fossils are known, which link together existing organisms with their likely ancestors
- sequence in which fossils appear matches the sequence in which they would be expected to evolve, with bacteria/simple algae appearing first, then fungi and worms, and then land vertebrates
- sequence fits with the ecology of the groups, with plant fossils appearing before animal, plants on land before animals on land, and plants suitable for insect pollination before insect pollinators
selective breeding of domesticated animals
- by breeding members of a species with a desired trait, the frequency of this trait becomes more common in successive generations
- targeted breeds can show significant variation in a (relatively) short period
- this shows that selection can cause evolution
homologous structures
Comparative anatomy of groups of organisms may show certain structural features that are similar, implying common ancestry
the evolution of homologous structures by adaptive radiation explains similarities in structure when there are differences in function
define adaptive radiation
when several new species rapidly diversify from an ancestral source, with each new species adapted to utilise a specific unoccupied niche
define homologous structures
Anatomical features that are similar in basic structure despite being used in different ways
speciation
- speciation is the evolutionary process by which two related populations gradually diverge into separate species that can no longer interbreed and produce fertile offspring
- the degree of genetic divergence between geographically separated populations will gradually increase the longer they are separated
patterns of variation
- continuous variation across the geographical range of related populations matches the concept of gradual divergence
- Darwin gave examples of populations that are recognisably different, but not the the extent that they are clearly separate species
- this disproves the idea that species were created as distinct types (and should be constant across their geographic range) or that they are unchanging
give an example of a homologous structure and explain its significance
the pentadactyl limb in a variety of different animals: mammals, birds, amphibians and reptiles all share a similar arrangement of bones in their appendages based on a five-digit limb
however, they may also be highly dissimilar according to the mode of locomotion:
eg Human hands are adapted for tool manipulation (power vs precision grip),
Bird and bat wings are adapted for flying, whale and dolphin fins are adapted for swimming
describe the development of melanistic insects in polluted areas
Peppered moths (Biston betularia) exist in two distinct forms – a light colouration and a darker melanic variant
- adult Biston betularia moths fly at night to try to find a mate and reproduce.
- during the day they roost on the branches of trees.
- birds and other animals that hunt in daylight predate moths if they find them.
- in unpolluted areas tree branches are covered in pale-coloured lichens and peppered moths are well camouflaged against them.
- sulphur dioxide pollution kills lichens. Soot from coal burning blackens tree branches.
- melanic moths are well camouflaged against dark tree branches in polluted areas.
- in polluted areas the melanic variety replaced the peppered variety over a relatively short time, but not in non-polluted areas
natural selection can only occur if
there is variation amongst members of the same species - if all individuals in a population were identical, there would be no way of some being favoured over others
give 3 sources of variation
- mutation - new alleles produced by gene mutations enlarge the gene pool of a population
- meiosis - produces new combinations of alleles by breaking up the existing combination in a diploid cell, through crossing over and the independent orientation of bivalents
- sexual reproduction involves the fusion of male and female gametes, ensuring a new combination of alleles.
define adaptations
characteristics that make an individual suited to its environment and way of life. these develop by natural selection over time.
species tend to
produce more offspring than the environment can support, which may lead to a struggle for existence within a population due to competition for resources
describe how natural selection leads to change within a species
- individuals that are better adapted tend to survive and produce more offspring while the less well adapted tend to die or produce fewer offspring
- individuals that reproduce pass on genetic characteristics to their offspring
natural selection thus increases the frequency of characteristics that make individuals better adapted and decreases the frequency of other characteristics leading to changes within a species.
give an example of adaptive radiation and natural selection
changes in beaks of finches on Daphne major
Different finch species demonstrated adaptive radiation and show marked variation in beak size and shape according to diet.
G. fortis’ diet consists of seeds, which when weather conditions are normal are plentiful, small, and soft, but which become fewer, larger, and tougher during times of drought
The Grants observed a wide range of beak sizes in G. fortis when weather conditions were normal, but found that during periods of drought beak size increased
This is because G. fortis were forced to feed on larger, harder seeds, which only the larger-beaked individuals were able to crack open, so most of the population died.
give 4 reasons why antibiotic resistance has grown so quickly
- there has been very widespread use of antibiotics, both for treating diseases and in animal feeds used on farms.
- bacteria reproduce very rapidly, with a generation time of less than an hour.
- populations of bacteria are often huge, increasing the chance of a gene for antibiotic resistance being formed by mutation.
- bacteria can pass genes on to other bacteria in several ways, including using plasmids, which allow one species of bacteria to gain antibiotic resistance genes from another species.
describe the process of development of antibiotic resistance
- there is a population with no antibiotic-resistant bacteria
- an antibiotic resistance gene is formed by mutation in one bacterium//received from a bacterium in another population
- population with some antibiotic-resistant bacteria
- when the antibiotic is used natural selection takes place
what is the binomial system?
a system of scientific names for species that is universal among biologists and has been agreed and developed at a series of congresses. this is applied whenever species are discovered
give 4 rules of the binomial system
- the genus name begins with an upper-case (capital) letter and the species name with a lower-case (small) letter.
- in typed or printed text, a binomial is shown in italics
- after a binomial has been used once in a piece of text, it can be abbreviated to the initial letter of the genus name with the full species name
- the earliest published name for a species is the correct one
how do taxonomists classify species?
using a hierarchy of taxa
state the 3 domains into which all organisms are classified
bacteria, archaea, eukaryota
