Natural Selection/Speciation (5.2, 10.3) Flashcards
Natural Selection
The process by which random, evolutionary changes are selected for by nature in a consistent, orderly, non-random way.
In simpler terms, the increase or decrease in the frequency of certain alleles within a population.
What did Darwin mean by ‘survival of the fittest’?
It is not necessarily the strongest or most intelligent species that survive, but the ones that are most responsive to change.
What are the key components of the process of Natural Selection? (Hint: Mnemonic).
- Inherited variation exists within the population
- Competition results from an overproduction of offspring
- Environmental pressures lead to differential reproduction
- Adaptations which benefit survival are selected
- Genotype frequency changes across generations hence
- Evolution occurs within the population
Define population
A group of organisms of the same species living in the same area at the same time.
Define gene pool
The sum total of all genes/alleles that are present in a population.
What are the contributors to genetic variation in a population?
Mutations - These add new alleles to a population
Meiosis (through independent assortment and crossing over) - Creates new gene combinations
Sexual Reproduction - Different zygotes are formed by random fertilisation
What is the Malthusian dilemma?
Populations multiply geometrically (i.e. exponentially) while food sources increase arithmetically (i.e linear).
What types of adaptations are there?
Structural - Physical differences in structure
Behavioural - Differences in patterns of activity
Physiological - Differences in detection and response by vital organs
Biochemical - Differences in enzyme and cell functions
Developmental - Variable changes across a life span (eg. ageing patterns, meiosis).
Why are allele frequencies in a gene pool of a population constantly changing?
Because if the environment changes, what constitutes a beneficial/detrimental trait is subject to change.
Describe how the Peppered moths show Natural Selection
There is a naturally occurring mutation for dark-coloured moth wings. However, the mottled wing moths had a higher survival rate and made up most of the Peppered moth’s population as it was able to camouflage against the lichen on trees and hide from predators. During the Industrial Revolution in the 19th century, the pollution from fossil fuels killed the lichen on the trees so the dark-coloured wing allele became the more beneficial trait for survival. Hence, the frequency of this allele increased. Then, in the 20th century once fossil fuel use decreased the mottled wing allele became more common once again as lichen regrew on the trees.
Describe the Galapagos finches
Different species of finch evolved on different islands. As each island had a different environmental habitat and food sources the finches underwent adaptive radiation. This is seen through the shapes of their beaks, which are adapted for different purposes.
Describe antibiotic resistance in bacteria
In a bacteria colony, over several generations, a proportion of the bacteria can develop a resistance to the antibiotic through genetic mutation. Then, the following generations become immune to this antibiotic and it is ineffective against the bacteria.
Define allele frequency
The proportion of a particular allele within a population.
What is the formula to find the allele frequency?
Allele frequency = specific allele/total number of alleles
Define gene flow
The movement of genes into/out of gene pools.
