Variation

Question 1

What is a species?

Answer 1

Organisms that can interbreed with each other and produce fertile offspring

Question 2

What is a population?

Answer 2

All the organisms of one species found in an area

Question 3

In a population, do the individuals look the same? Why?

Answer 3

Not all the individuals will be the same;

• Mutations can occur
• Which lead to genetic variation
• So, individuals will have different characteristic/ show different phenotypes
• This is usually extensive as the species is likely to have been in existence for a long time

Question 4

What is evolution?

Answer 4

The change in the inherited characteristics of a population over tine through a process of natural selection which may result in the formation of new species

Question 5

How does evolution occur through natural selection?

Answer 5

1. There are differences in the genetic make-up of organisms
2. Individual organisms have to compete for limited resources (e.g. food, water, mates etc) and compete to escape from predation
3. Organisms that have traits that make them better adapted to the environment (due to their genetic variation) are able to compete more effectively, and thus have a better chance of surviving and reproducing
4. These organisms pass on their beneficial genes to their offspring
5. Organisms that are less well adapted are selected against - they are more likely to die before they get the chance to breed and pass their undesirable genes to their offspring
6. Over many generations, the advantageous genes accumulate in the population and the disadvantageous genes are lost
7. On the whole, the species evolves to adapt to its environment

Question 6

What are the 2 sources of variation?

Answer 6

1. Variation can be genetic/ inherited
   OR
   2.Variation can be environmental

Question 7

How does inherited/ genetic variation occur?

Answer 7

• Mutations:
• Mutations are changes in the sequence of bases in DNA
• Mutations can be inherited; passed on to subsequent generations
• May alter the functioning of the protein that the mutant gene codes for
• Leading to an altered characteristic
• This can be expressed in the phenotype

Question 8

Explain how bacteria became resistant to antibiotics used to treat bacterial infections

Answer 8

• Within a population of bacteria there would be genetic variation
• Some individuals would have had (by chance) a mutation that made them resistant to antibiotics
• This mutation is in a gene found in plasmid DNA.
• When antibiotics were used, by humans, to treat bacterial infections, the antibiotics were successful against the majority of bacteria
• but were ineffective against those variants that had the antibiotic resistance gene
• They had a selective advantage
• Were more likely to survive.
• These surviving bacteria reproduced through binary fission
• The antibiotic resistance gene became more common in the bacterial population
• This has continued to occur over many generations