9B Selection pressures Flashcards
Evolution
The continual process of change in species of living things
Natural selection
The differential survival and reproduction of individuals in a species based on heritable differences in their phenotypes.
Acquired characteristics
An acquired characteristic is one that an individual develops during it’s lifetime
Genotypic variation
The genetic differences between individuals
Phenotypic variation
The physical, structural, physiological or behavioral differences between individuals
Darwin’s observation #1
There is phenotypic variation within species
In any species of any population the physical characteristics
( phenotypes ) have variation.
Darwin’s observation #2
Offspring tend to inherit the traits of their parents
The offspring inherits phenotypic traits that the parents have e.g., hair colour and height.
Darwin’s observation #3
Species produce more offspring than required to replace themselves
Most species have more offspring than what would replace the parents. e.g., turtles producing average of 80 eggs / nest when they only need 2.
Darwin’s observation #4
There is a struggle to survive
Some animals don’t hatch or are eaten by other animals. For example sea turtles are often eaten by sea birds before they make it to sea
Selection pressure
The environmental factor which causes differential death in members of a species due to their phenotypic variation
Selecting agent
The element of the environment that exerts a selection pressure.
Fitness
The relative chance that an individual will contrivute to the gene pool of the next generation
Selective advantage
a synonym for fitness
Darwin’s first inference
- Individuals whose traits give them more chance to survive and reproduce leave more offspring than other individuals.
Allele frequency
The fraction ( or percentage ) of chromosomes in a population that carry a specific allele
Darwin’s second inference
- The unequal chance of reproduction will lead to accumulation of favorable traits in the population over generations.
Sexual selection
A form of natural selection in which the selection pressure is the ability to obtain a mate
Female choice
Tournament species
One sex ( usually males ) fight with each other for the right to mate with all the females
Explain why natural selection reduces genetic diversity.
Natural selection reduces the genetic diversity of a population as it is reducing the ‘ unfit ‘ phenotypes leaving less diversity. This is the opposite of mutations which increase the diversity.
Explain why natural selection is often stabilising.
Natural selection is often stabilising meaning that natural selection removes the unfit phenotypes and narrows It down so they are mostly the same.
Explain what causes directional selection
change in the environment e.g. new predator/ disease / temperature, selection pressure may change. suddenly advantage for uncommon phenotype. Natural selection eliminates all the disadvantaged species.
What increases genetic mutation?
Genetic mutation is increased by creating new alleles increases the genetic diversity
What decreases genetic mutation?
natural selection decreases as it selects against certain mutations that are unfavourable
