Variation and Selection Flashcards
(17 cards)
What is variation?
The differences between individuals.
What is intraspecific variation?
Differences between organisms of the same species.
What causes variation?
Genetic and environmental factors.
What are the genetic factors that cause variation?
- Genetic crossing over
- Independent crossing over
- Random fertilisation
- Mutations in the DNA
What are the environmental factors that affect variation?
food, climate and lifestyle
What is continuous variation?
Quantitative data can take a range of different values.
What is discontinuous variation?
Qualitative data can only take certain values.
What is evolution?
The frequency of an allele changes over time.
What are the two ways in which evolution can happen?
- Natural Selection.
- Genetic Drift.
Describe how natural selection leads to evolution?
Some organisms have alleles that make them better adapted to deal with certain selection pressures making them more likely to survive to breed and reproduce. They then pass on that allele to their offspring which are more likely to survive to reproduce and pass on their genes. Over time. the frequency of that allele will increase from generation to generation and that leads to evolution.
What are selection pressures?
Pressures that affect an organism’s chance of surviving.
What is stabilising seletion?
Organisms have alleles that code for characteristics towards the middle of two extremes.
What is an example of stabilising selection?
baby birth weight
What is directional seletion?
Organisms have alleles that code for a single extreme characteristic.
What is an example of directional selection?
antibiotic-resistant bacteria.
What is disruptive selection?
Organisms have alleles that code for extreme characteristics.
What is an example of disruptive selection?
The size of a bird’s beak. When there are only small or big seeds only birds with either big or small beaks will be able to eat those seeds. Birds with medium-sized beaks won’t be able to eat either meaning they will be less likely to survive and pass on their alleles.
