Evolution by Natural Selection Flashcards
All 7 cards in this deck
What is evolution?
The gradual change in the inherited characteristics of a population over time, over many generations.
What are the steps of evolution by natural selection?
e.g. a population of beetles on green leaves, some green and some brown
- There is variation in the population caused by different alleles — some beetles are green, some brown.
- Those best adapted survive and reproduce; others are eaten or die — green beetles are camouflaged and survive.
- Survivors pass the advantageous allele to their offspring, so it becomes more common each generation — the population becomes mostly green.
How does camouflage increase an organism's chance of survival and reproduction?
e.g. a bittern hidden among reeds
It makes the organism harder for predators to see, so it is more likely to survive, breed and pass on the alleles for camouflage.
True or false? Bacteria become resistant because the antibiotic causes them to change so they can survive.
False. The resistance arises from a random mutation that happens by chance; the antibiotic only selects the bacteria that already have it.
A graph shows the percentage of bacteria resistant to an antibiotic rising year on year. What conclusion can be drawn?
The resistant bacteria have a survival advantage and are being selected for, so resistance is increasing in the population by natural selection — evidence supporting Darwin's theory.
Why can natural selection not help a population with very low genetic variation to survive a new disease?
e.g. a population of closely related cheetahs
Few or none of the individuals carry an advantageous (resistance) allele, so very few survive to reproduce and pass it on.
True or false? A population of closely related individuals has a higher risk of extinction than one with high genetic variation.
True. With little variation, it is unlikely that any individual has alleles giving an advantage if the environment changes, so the whole population may die out.