Evolution Flashcards
Define biological evolution
A change in the allele frequency of a population’s gene pool over successive generations
How do fossils provide evidence for evolution?
The fossil record provides evidence by revealing the features of an ancestor for comparison against living descendants
What is the fossil record and what does it show?
The totality of fossils, both discovered and undiscovered, is referred to as the fossil record
The fossil record shows that over time changes have occurred in the features of living organisms (evolution)
What are fossils and what two categories can they be divided into? What different types of evidence may they provide?
A fossil is the preserved remains or traces of any organism from the remote past
Preserved remains (body fossils) provide direct evidence of ancestral forms and include bones, teeth, shells, leaves, etc.
Traces provide indirect evidence of ancestral forms and include footprints, tooth marks, burrows and faeces (coprolite)
Explain the law of fossil succession
his chronological sequence of complexity by which characteristics appear to develop is known as the law of fossil succession
This ordered succession of fossils suggests that newer species likely evolved as a result of changes to ancestral species
Explain how strata form and how this provides information on the sequence of development
Fossils can be dated by determining the age of the rock layer (strata) in which the fossil is found
Sedimentary rock layers develop in a chronological order, such that lower layers are older and newer strata form on top
Each strata represents a variable length of time that is classified according to a geological time scale (eons, eras, periods)
Define transitional fossils, explain the. significance and provide an example
Transitional fossils demonstrate the intermediary forms that occurred over the evolutionary pathway taken by a single genus
They establish the links between species by exhibiting traits common to both an ancestor and its predicted descendents
An example of a transitional fossil is archaeopteryx, which links the evolution of dinosaurs (jaws, claws) to birds (feathers)
What may be a limitation to the use of fossils to evaluate evolutionary links?
Only the hard parts of an organism are typically preserved, meaning usually only fragments of remains are discovered
With limited fossil data, it can be difficult to discern the evolutionary patterns that result from ancestral forms
What may be a limitation to the use of fossils to evaluate evolutionary links?
Only the hard parts of an organism are typically preserved, meaning usually only fragments of remains are discovered
With limited fossil data, it can be difficult to discern the evolutionary patterns that result from ancestral forms
Define selective breeding and explain how it provides evidence for evolution
Selective breeding is a form of artificial selection, whereby man intervenes in the breeding of species to produce desired traits in offspring
By breeding members of a species with a desired trait, the trait’s frequency becomes more common in successive generations
Selective breeding provides evidence of evolution as targeted breeds can show significant variation in a (relatively) short period
Provide an example of selective breedng in the plant kingdom
Plants of the genus Brassica have been bred to produce different foods by modifying plant sections through artificial selection
This includes broccoli (modified flower buds), cabbage (modified leaf buds) and kale (modified leaves)
Provide two examples of selective breeding in the animal kingdom
Example 1: Horse Breeding
Horses have been selectively bred across many generations to produce variation according to a targeted function
Race horses have been bred for speed and hence are typically leaner, lighter, taller and quicker
Draft horses have been bred for power and endurance and hence are sturdier and stockier
Example 2: Cow Breeding
Cows have been selectively bred across many generations to produce offspring with improved milk production
Farmers have also targeted the breeding a cows with a mutation resulting in increased muscle mass
The resulting stock of cattle (termed Belgian Blue) have excessive bulk and produce more edible lean meat
Example 3: Dog Breeding
Dog breeds show an enormous amount of variety due to the targeted selection of particular traits by man
Hunting dogs (e.g. beagles) were typically bred to be smaller in stature so as to enter fox holes
Herding dogs (e.g. sheep dogs) were bred for heightened intelligence in order to follow herding commands
Racing dogs (e.g. greyhounds) were specifically bred to be sleek and fast
Toy dogs (e.g. chihuahuas) were selectively bred for their dimunitive size
How may comparing anatomy allow for ancestry to be established?
Comparative anatomy of groups of organisms may show certain structural features that are similar, implying common ancestry.
The more similar the homologous structures between two species are, the more closely related they are likely to be as the species would have had less time to evolve
What are homologous structures and how why does this occur?
Anatomical features that are similar in basic structure despite being used in different ways are called homologous structures
This occurs when species rapidly diversify from their common ancestor by adapting their function to a unique niche. This is known as adaptive radiation.
Discuss homologous structures with reference to an example
A classical example of homologous structures is 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
Despite possessing similar bone arrangements, animal limbs may be highly dissimilar according to the mode of locomotion:
-Human hands are adapted for tool manipulation (power vs precision grip)
-Bird and bat wings are adapted for flying
-Horse hooves are adapted for galloping
-Whale and dolphin fins are adapted for swimming
Discuss divergence in species [ 4 marks ]
Within a population of any given species there will be genetic variation (i.e. variation which is inheritable) Typically this variation will be continuous and follow a normal distribution curve as the rate of change is gradual and cumulative
If two populations of a species become geographically separated then they will likely experience different ecological conditions Over time, the two populations will adapt to the different environmental conditions and gradually diverge from one another
The degree of divergence will depend on the extent of geographical separation and the amount of time since separation occurred
Populations located in close proximity that separated recently will show less variation (less divergence) Distant populations that separated a longer period of time ago will show more variation (more divergence)
How does speciation occur once species are geographically seperated ?
The degree of divergence between geographically separated populations will gradually increase the longer they are separated
As the genetic divergence between the related populations increase, their genetic compatibility consequently decreases
Eventually, the two populations will diverge to an extent where they can no longer interbreed if returned to a shared environment
When two populations can no longer interbreed and produce fertile, viable offspring they are considered to be separate species
Define speciation
The evolutionary process by which two related populations diverge into separate species is called speciation
Discuss evolution in connection to peppered moths
Peppered moths (Biston betularia) exist in two distinct polymorphic forms – a light colouration and a darker melanic variant
In an unpolluted environment, the trees are covered by a pale-coloured lichen, which provides camouflage for the lighter moth
In a polluted environment, sulphur dioxide kills the lichen while soot blackens the bark, providing camouflage for the dark moth
The frequency of the two different forms of peppered moth is dependent on the environment and evolves as conditions change
Before the industrial revolution, the environment was largely unpolluted and the lighter moth had a survival advantage
Following the industrial revolution, the environment became heavily polluted, conferring a survival advantage to the darker moth
Those possessing the advantage are more likely to survive and reproduce passing on the advantageous gene
What are the key component of natural selcetion?
I - Inherited variation exists within the population
C - Competition results from an overproduction of offspring
E - Environmental pressures lead to differential reproduction
A - Adaptations which benefit survival are selected for
G - Genotype frequency changes across generations
E - Evolution occurs within the population
ICE AGE
What two types of variation exist?
This variation can manifest as either discontinuous (distinct classes) or continuous (range across a characteristic spectrum)
What are the main mechanisms by which genetic variation between individuals in a species may occur:
Mutations – Changing the genetic composition of gametes (germline mutation) leads to changed characteristics in offspring
Meiosis – Via either crossing over (prophase I) or independent assortment (metaphase I)
Sexual reproduction – The combination of genetic material from two distinct sources creates new gene combinations in offspring
Define gene mutation
A gene mutation is a change in the nucleotide sequence of a section of DNA coding for a specific trait
How does meiosis cause genetic variation?
- Crossing Over
Crossing over involves the exchange of segments of DNA between homologous chromosomes during prophase I
The exchange of genetic material occurs between non-sister chromatids at points called chiasmata
As a consequence of this recombination, all four chromatids that comprise the bivalent will be genetically different
Chromatids that consist of a combination of DNA derived from both homologous chromosomes are called recombinants
Offspring with recombinant chromosomes will have unique gene combinations that are not present in either parent
- Independent Assortment
When homologous chromosomes line up in metaphase I, their orientation towards the opposing poles is random
The orientation of each bivalent occurs independently, meaning different combinations of maternal / paternal chromosomes can be inherited when bivalents separate in anaphase I
The total number of combinations that can occur in gametes is 2n – where n = haploid number of chromosomes
Humans have 46 chromosomes (n = 23) and thus can produce 8,388,608 different gametes (223) by random orientation
If crossing over also occurs, the number of different gamete combinations becomes immeasurable
How does sexual reproduction lead to variation?
The fusion of two haploid gametes results in the formation of a diploid zygote
This zygote can then divide by mitosis and differentiate to form a developing embryo
As meiosis results in genetically distinct gametes, random fertilisation by egg and sperm will always generate different zygotes
This means that individual offspring will typically show variation despite shared parentage
How does competition form between species
If left to follow course, a stable population will inevitably outgrow its resource base, leading to competition for survival
When there is an abundance of resources, a population will grow according to its biotic potential (exponential curve)
With more offspring, there are less resources available to other members of the population (environmental resistance)
This will lead to a struggle for survival and an increase in the mortality rate (causing population growth to slow and plateau)
What are adaptations and how may they be classified?
Adaptations are features of organisms that aid their survival by allowing them to be better suited to their environment
These adaptations may be classified in a number of different ways:
-Structural: Physical differences in biological structure (e.g. neck length of a giraffe)
-Behavioural: Differences in patterns of activity (e.g. opossums feigning death when threatened)
-Physiological: Variations in detection and response by vital organs (e.g. homeothermy, colour perception)
-Biochemical: Differences in molecular composition of cells and enzyme functions (e.g. blood groups, lactose tolerance)
-Developmental: Variable changes that occur across the life span of an organism (e.g. patterns of ageing / senescence)
