Topic 4 - Natural Selection And Genetic Modification Flashcards
Darwin’s theory of evolution
• Individuals in a population show genetic variation because of differences in their alleles, these differences arise from mutations.
• There is a selection pressure that affects an organism’s chance of survival (predation, competition for resources).
• Those individuals with characteristics that make them better adapted to the selection pressures in their environment are more likely to survive and reproduce.
• The advantageous allele/characteristic is passed on to their offspring. This continues and over time the mutation is more common in the population. This is survival of the fittest.
Evidence for evolution:
Bacteria
• Bacteria sometimes develop random mutations in their DNA. These can create new alleles which can change the bacterias characteristics.
• One of these mutations may give them resistance to an antibiotic.
• If an organism is infected with bacteria and some of them have resistance, they are likely to survive the treatment with antibiotics.
• For bacterium, the ability to resist the antibiotic is a big advantage, a resistant bacterium is better able to survive than a non-resistant bacterium - and so it lives for longer and reproduces many more times.
• This leads to the allele for resistance being passed on to lots of offspring - it’s natural selection.
How is bacteria evidence for evolution?
Antibiotic resistance provides evidence for evolution because it makes the bacteria better adapted to an environment in which antibiotics are present. And as a result, antibiotic resistance becomes more common in the population over time. The emergence of other resistant organisms also provides evidence for evolution.
Evidence for evolution:
Fossils
• Generally, the deeper the rock, the older the fossil.
• Radiometric dating - by measuring the presence of a short-life radioactive element e.g. carbon-14.
• Comparing the fossil to other tools/fossils that have been dated.
• Comparing the fossil to other finds from the same layer of rock.
• By arranging fossils in chronological order, gradual changes in organisms can be observed.
This provides evidence for evolution because it shows how species have changed and developed over billions of years.
Ardi from 4.4 million years ago
• The fossil was described as having a mixture of human and ape like characteristics.
• Large ape-like big toes for grasping branches suggests Ardi climbed trees.
• The leg structure indicates that Ardi walked upright.
• Long arms and short legs are more ape like.
• Ardi’s hands show that she did not use them to help her walk as apes do.
• The brain was a similar size to a chimpanzee.
Lucy from 3.2 million years ago
• The fossil was also described as having a mix of human and ape like characteristics.
• Lucy us more human like than Ardi.
• The length of the arms and legs are in between an ape and a human.
• The feet have an arch and are adapted to walking rather than climbing.
• The leg structure indicates that Lucy walked upright and more efficiently than Ardi.
• The brain was a similar to size to a chimpanzee but slightly larger than Ardi’s.
“Turkana Boy” Homo erectus from 1.6 million years ago
• In 1984 his team discovered a 1.6 million year old fossil of the homo erectus species.
• The fossil was named Turkana Boy after the region it was found in.
• Turkana Boy still has a mixture of human and ape like characteristics.
• The feet and leg structure show he walked upright and was better suited to this than Lucy.
• The length of the arms and legs were much more like humans than apes.
• The brain was larger than Lucy’s and similar to that of a human.
How are stone tools made?
Stone tools made by hitting rock together and refining them.
How are stone tools evidence for evolution?
Over time the stone tools have become more complex indicating that humans have become more intelligent which is further backed up by an increase in brain volume.
How does a scientist work out how old stone tools are?
• Looking at the structural features of the tool or fossil.
• Using stratigraphy - the study of rock layers. Older rock layers are normally found below younger layers, so tools or fossils in deeper layers are usually older.
• Stone tools are usually found with carbon-containing material e.g. a wooden handle. Carbon-14 dating can be used to date this material.
Common ancestor
Humpback whales and dolphins are thought to have evolved from an animal that lived about 40 million years ago, this is called a common ancestor (last common ancestor).
Why were some classifications based on characteristics were wrong?
Because the characteristics were similar due to adaptation to the same environment.
Why is genetic evidence better than evidence from observable characteristics for classification?
This is because DNA is not changed by the environment. Similar DNA means similar inheritance.
Three domains:
Bacteria
• No nucleus
• No unused DNA
Three domains:
Archaea
• No nucleus
• Unused DNA
Eukarya
• Animals
• Fungi
• Plants
• Protists with cilia
• Protists with flagella
All have a nucleus.
Explain how DNA sequencing techniques can be used to determine relationships between organisms?
The DNA sequences for the same gene in different organisms can be compared the more similar the DNA base sequence the more closely related the organisms are.
Explain how genetic analysis led to the prokaryote kingdom being split into two domains?
Genetic analysis led to the discovery that members of the prokaryote kingdom were not as closely related as previously thought so it was suggested that the organisms in it were split into the two domains of archaea and bacteria.
Selective breeding
A process where humans select desirable features within an organism and breed them over many generations until the desirable characteristic is present in greater number in the population.
Examples:
• Dogs
• Horses
• Cows
• Cabbages
• Wheat
Selective breeding prcess
- Identify organisms with desirable characteristics.
- Cross breeding of selected individuals
- Select the best offspring and continue to breed.
- Repeat the process over many generations.
- Over time, the desirable characteristics increases in appearance.
Advantages and disadvantages of selective breeding?
+ Produces organisms with desirable features.
- Reduction in genetic variation.
- Vulnerable to disease.
- Organisms could have genetic defects.
- Takes place over many generations.
When selective breeding plants, what are the desirable characteristics?
• Disease resistance
• Increased yield
• Coping with the environment e.g. drought
• Fast growth
• Nutrition
Genetic engineering
Modifying an organisms genome (its DNA) to introduce desirable characteristics. This involves the use of enzymes and vectors (carriers).
Enzymes involved in genetic engineering
• Restriction enzymes recognise specific sequences of DNA and cut the DNA at these points - the DNA are left with sticky ends where they have been cut.
• Ligaze enzymes are used to join 2 pieces of DNA together at their sticky ends.
Two different bits of DNA stuck together are known as recombinant DNA. 
