6.3 Inheritance, Variation and Evolution (genetics and evolution) Flashcards
Outline the theory of evolution by natural selection
- individuals of a species show a wide range of variation for a characteristic
- those with the characteristic most suited to the environment will survive breed most successfully
- the desirable characteristic that has enabled the individuals to survive are passed onto their offspring
Why was Darwin’s theory of evolution not accepted initially?
- most people believed in creationism
- insufficient evidence to prove the theory
- the mechanism of variation and inheritance was not known at the time
What was Jean-Baptiste Lamarck’s theory of inheritance?
That changes during the lifetime of an organism can be inherited
What is speciation?
The formation of a new species, when two populations become so varied that they cannot interbreed to produce a fertile offspring
What is the definition of a species?
A group of organisms with similar characteristics which are able to interbreed to produce a fertile offspring
Outline the process of speciation through geographic isolation
- Two populations of the same species are separated geographically
- geographic isolation prevents interbreeding and mixing of genes between the populations
- due to different selection pressures, different mutations occur producing different phenotypes in each population
- over time, the two populations may evolve so that they are not able to interbreed
Why is genetic variation important in speciation?
genetic variation produces phenotypic variation, some of which are better suited to the environment and are selected for
How did Mendel study inheritance?
through carrying breeding experiments on plants and analysing the ratio of characteristics in offsprings
Why was Mendel’s work not recognised until after his death?
- he could not explain the mechanism of inheritance, as chromosomes were only discovered after his death
- it was not communicated well to other scientists and not published in a reputable scientific journal
State two kinds of evidence used to show evolution
- fossils
- antibiotic resistance in bacteria
How are fossils formed?
- parts of organisms that have not decayed due to conditions needed for decay being absent
- parts of organisms that have been replaced by minerals as they decay. e.g bones
- traces of organisms are preserved, covered in sediment and becoming rock
Why are there few traces of early life-forms left behind?
they are mostly soft-bodied
How do fossils act as evidence for evolution?
scientists can identify the ages of the fossils and use them to show how organisms change over time
What do branches in evolutionary trees indicate?
where speciation has occurred
What is extinction?
where there are no individuals of a species still alive
