Paper 2: Topic 6 Inheritance, variation & evolution - Variation & evolution (UV) Flashcards
Define the term variation
Differences in the characteristics of individuals within a population
State 3 causes of variation within a population
- Genetics
- Environment
- Combination of genetics and the environment
Explain how genetics can lead to variation in a population
- Different individuals will inherit different combinations of alleles
- The different combination of alleles will cause differences in the proteins that are or are not produced
- This will cause differences in the characteristics in the different individuals
- E.g. eye colour, blood group, genetic disorders such as cystic fibrosis
Explain how the environment can lead to variation within a population
Different environmental factors can affect certain characteristics in individuals
e.g.
- Road accident → loss of a limb
- Exposure to UV light → affects melanin content of the skin
Explain how genetics and the environment can lead to variation in a population
Individuals who possess certain genes and are exposed to certain environmental factors can have different characteristics e.g.
- skin colour (affected by UV light and gene for melanin production)
- body mass (affected by quality and quantity of diet and the genes for muscle development and growth)
State what factors influence most physical characteristics
Genetics AND the environment
State what causes variation within a population
Mutations
Describe the range of variation observed in most populations
- Extensive
- This means there is a wide range of variants for most characteristics within a population
Define the term ‘evolution’ Hint: 3 key parts to this definition
- A change in the inherited characteristics of a population over time
- Through a process of natural selection
- Which result in the formation of a new species
Explain the theory of natural selection
- A mutation occurs within an individual in a population
- This causes variation to develop within a population
- Some individuals are more suited to their environment (due to the characteristics they possess)
- The individuals who are more suited to the environment are more successful
- These individuals are more likely to survive and breed
- These individuals will pass on the alleles for the beneficial characteristics to the their offspring
- Over a LONG period of time and MANY generations the beneficial alleles will become more common in the population
- Over time the variants that posses the best phenotypes are selected for and increase in number
Define the term ‘selective breeding’
Selective breeding (artificial selection) is the process by which humans breed plants and animals for particular genetic characteristics
State 2 examples of how Humans have used selective breeding for centuries
Humans have been doing this for thousands of years.
They have used it to:
* produce food crops from wild plants and
* bred domesticated animals.
State the 4 key steps in artificial selection/selective breeding
- Selective breeding involves choosing parents with the desired characteristic from a mixed population
- They are bred together
- From the offspring those with the desired characteristic are bred together
- This continues over many generations until all the offspring show the desired characteristic
Give 4 features that have been selected for in selective breeding
- Disease resistance in food crops
- Animals which produce more meat or milk
- Domestic dogs with a gentle nature
- Large or unusual flowers
State 3 disadvantages of using artificial selection / selective breeding
- Inbreeding can result in a reduced gene pool
- Inbreeding can result in health problems
- Inbreeding results in reduced variation within the population
Explain what is meant by the expression ‘reduced gene pool’
The number of different alleles in a population decreases
Explain how artificial selection can result in health problems in the population
- Selective breeding can lead to ‘inbreeding’ where some breeds are particularly prone to disease or inherited defects
- This is because of a reduced gene pool
Explain how artificial selection can reduce the gene pool
The number of alleles in the population can be decreased over time
This is because some alleles are selected AGAINST so their frequency in the population decreases
Over time this reduces the total number of alleles present in the population
Explain how artificial selection can cause problems if a new disease occurs
- As a result of selective breeding there is less variation in a population
- So all the individuals in the population have very similar characteristics
- This means that if one individual is likely to be killed by the new disease then all the individuals in the population are also likely to die from the new disease
- This is because there is less chance of any resistant alleles being in a population
Give 3 reasons why a gardener/farmer may use selective breeding
- To produce a crop with higher yield
- To produce a crop with more fruits
- To produce a crop with larger fruits