Classification and Evolution Flashcards
State the Linnaean classification system
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
Describe the taxonomic classification system
In the Linnaean system, Each organism is categorised based on a number of different groups.
These groups are called taxonomic groups
Each individual group is referred to as a taxon
Together they are called taxa
The taxonomic system is hierarchical.
Means that we have the broadest groups at the top and the most specific at the bottom.
E.g. every type of organism falls into one of the three domains
Organisms are then subdivided into increasingly specific categories based on common features
At the bottom of the system, we have the most specific category which is the species (only one type of organism)
Describe what is meant by a species
A species is a group of organisms that can reproduce to produce live, fertile offspring
horse mate with donkey. offspring mule which is infertile
So because horses and donkeys cannot reproduce to produce fertile offspring, horses and donkeys are separate species
Use the binomial naming system
The binomial name simply consists of the genus and species
(genus first)
Only the first letter of the genus is a capital letter in the binomial name
Describe what is meant by interspecific variation
differences = variation
The differences between different species are called interspecific variation
Interspecific variation is often very significant
Different species can show marked differences e.g. in their body shape, how they get their food and how they reproduce
Describe what is meant by intraspecific variation
Variation between members of the same species
E.g. within cats there is significant variation in their fur colour .
Variation within a species is less pronounced than variation between different species
Causes of variation
Genetic
Environmental
Describe the genetic causes of variation
Caused by the genetic material that an organism inherits
Two members of the same species may inherit different alleles of a gene
E.g. alleles inherited by a cat will determine the colour and pattern of the cats fur
Sometimes a change can take place in the DNA sequence of a gene.
This is called a mutation
Mutations can lead to genetic variation
Sometimes a mutation can take place in a body (or somatic) cell
A good example are mutations which can lead to cancer such as skin cancer
Because these mutations do not affect gametes
They are not passed onto offspring
If a mutation is present in an organism’s gametes, then that mutation can be passed on to the offspring
Describe the environmental causes of variation
In humans e.g. scars from operations
E.g. flower colour in hydrageas
In acidic soil, these flowers are blue
while in alkaline soil the flowers are pink
Characteristics are often caused by a combination of genetics and the environment
Human height is influenced by both genetics and diet
Describe what is meant by anatomical, behavioural and physiological adaptations
Anatomical adaptations are adaptations to the physical features of an organism
E.g. eyespots, streamline body shape
Behavioural adaptations are adaptations is how an organism acts or behaves
Some behavioural adaptations are innate (they are passed on through genes) e.g. web building in spiders
Other behavioural adaptations may be learned- primates using sticks to probe for insects
Many behavioural adaptations are a combination of innate and learned
Physiological adaptations are adaptations to the way an organism’s biological processes function
E.g. antifreeze proteins produced by certain fish, plants and insects
All three types of organisms do not share any recent common ancestor
This means that antifreeze proteins must have evolved independently in these group of independents
When unrelated organisms evolve common features like this - called convergent evolution
Evolution by Natural selection
Organisms adapt to the conditions in their environments
Describe the process of evolution by natural selection
In any population of organisms, there is variation
A lot of this variation is due to the alleles present
The alleles present in a population is called the gene pool
Mutations are constantly taking place within the population
In many cases these mutations are harmful
However in some cases, a mutation can lead to a new , advantageous allele
The organism with the mutation has a better chance of detecting predators than others organisms of the same species
That means that this organism is more likely to survive and reproduce
Organisms without the advantageous allele are more likely to be killed by a predator
Referred to as survival of the fittest
When the organism with the advantageous allele reproduces, the allele can be passed on to its offspring
The offspring with the advantageous allele as more likely to avoid predation, survive and reproduce
Over time, the advantageous allele becomes widespread within the population
The frequency of the advantageous allele has increased in the gene pool
Over time, natural selection can lead to the development of new species
Evolution by natural selection usually takes place over a very long time period
Examples where this is more rapid. E.g. in bacteria and Introduction of antibiotics
Describe how evolution by natural selection can lead to antibiotic resistance in bacteria and pesticide resistance in insects
When antibiotics became more commonly used, atrial selection lead to the development of antibiotic-resistant bacteria
The presence of antibiotics was the selection pressure driving natural selection
Natural selection is also seen when insects are treated with pesticides
Selection pressures meaning
Selection pressures are factors that affect the survival of organisms in an environment
Selection pressures such as predation or the availability of food lead to the process of natural selection
Genetic causes of variation in organisms which reproduce by sexual reproduction
Genetic variation due to alleles and mutations apply to every organism, including those that reproduce by asexual or sexual reproduction
In organsims that carry out asexual reproduction, mutations are the only way that genetic variation can increase
However in organisms that reproduce by sexual reproduction genetic variation can increase in three other ways
Offspring produced by sexual reproduction will receive alleles from two different parents.
Means they will have a combination of features, inherited from these two parents
When an organism produces gametes, each of those gametes is genetically differemt
During meiosis, chromosomes are shuffled by independent assortment. Genetic material is exchanged between chromosomes during crossing over
Because gametes are genetically different, this produces genetic variation in an organisms offspring
Organisms that reproduce by sexual reproduction often produce a very large number of gametes
Fertilization between these gametes is a random process
We cannot predict which male gamete and which female gamete will fuse during fertilisation
This as a result introduces genetic variation between the offspring
characteristics which are purely genetic
– blood group and genetic conditions e.g. cystic fibrosis
Two categories of variation
Discontinuous (discrete)
Continuous
Describe what is meant by continuous variation
Feaures showing continuous variation can have any value within a range (this is called a continuum of values) between the smallest value and the greatest value
Continuous variation is normally represented using a histogram, overlaid with a curve
Good example is height - of continuous variation
Features that show continuous variation are usually controlled by several genes working together
These are called polygenes.
e.g. 80% of variation in human height is genetic.
remaining variation is due to environmental effects. e.g. diet
Normal distribution features
When we plot continuous variation (as a curve), this is called a normal distribution curve
The mean, median and mode are the same and are the measurement under the peak of the curve (vertical line downwards from the peak of the curve)
From a symmetrical curve - 50% of the values are less than the mean - 50% values greater than the mean
normal distribution curve is symmetrical about the mean
large number of features demonstrate a normal distribution
The spread of a normal distribution, gives us an idea of the amount of variation
tightly clustered around the mean- less variation
greater spread around the mean - more variation
Describe what is meant by discontinuous variation with examples
With discontinuous variation, a feature can only have specific valuesl, with no in-between values
Bar charts are generally used to represent features showing discontinuous variation.
E.g. human blood group
falls into four possible values
A B AB O
Discontinuous features are often controlled by a single gene
Calculate standard deviation
We can quantify the spread of the data by calculating the standard deviation
https://cdn.savemyexams.com/uploads/2020/11/Calculating-Standard-Deviation.png
smaller standard deviaion = more tightly clustered the values are around mean and the less variation there is in the data
greater standard deviation = less tightly clustered around mean
on the graph 68% of all values lie within 1 standard deviation of the mean
95% of values lie within 2 standard deviations of the mean
Describe stabilising selection
Stabilising selection takes place when environmental conditions are not changing
In stabilising selection, any extremes of phenotype are selected against. In this case, the extremes of phenotype are very low/high birth weight
Babies with a very low or high birth weight were less likely to survive than those with a birth weight around the mean. Example of stabilising selection
Since genetics play a major role in birth weight, because babies with a low or very high birth weight are less likely to survive, the alleles contributing to these birth weights are less likely to be passed on.
This means that over time, birthweights will stabilise towards the mean. (with less variation at the extremes)
Directional selection
Directional selection takes place when environmental conditions are changing (when the environment changes)
in the case of antibiotic resistant, the environmental change is the presence of antibiotics (antibiotic acting as a selection pressure)
In directional selection, one phenotype is selected over another phenotype
Example beak size of birds
Beak size varies around the mean
If climate becomes drier, plants produce harder seeds
Birds with a smaller beak size struggle to open the seeds for food
Birds with a larger beak size have a selective advantage and are more likely to survive and reproduce.
Over time, the alleles for larger beak size become more common in the gene pool.
The effect of this is to shift the mean towards a larger beak size
Example of directional selection
Another example is seen with antibiotic resistance in bacteria
This resistance occurs when a bacterium acquires a random mutation to a gene
In the absence of antibiotic, resistant bacteria have no advantage over non-resistant bacteria
So in the absence of antibiotic, the number of bacteria with antibiotic resistance is low
However in the presence of antibiotic, resistant bacteria have a selective advantage
Resistant bacteria can survive and reproduce in the presence of antibiotic whereas non-resistant bacteria are killed by the antibiotic
Over time, the gene for antibiotic resistance
becomes more common in the population
