evolution by natural selection Flashcards
what is genetic diversity
the total number of different alleles in a. population which enables natural selection and is caused by many different combinations of alleles, mutations, crossing over in meiosis and independent assortment
why is genetic diversity beneficial
prevents extinction by having a range of alleles and phenotypes to survive disease and changes. some phenotypes are advantageous- can survive and adapt to
describe the process of natural selection (giraffe example)
random gene mutation creates a new allele for a long neck/ specific characteristic
the individual with the long neck have an advantage because they can reach more leaves
the giraffe is more likely to survive, reproduce, and pass on the favourable allele
this repeats over many generations and allele frequency increases
what is stabilising selection
if environmental conditions remain constant, natural selection favours organisms that are already well adapted new extreme phenotypes are selected against
what is directional selection
if environmental conditions change, natural selection favours organisms with alleles for an extreme phenotype
What happens is stabilising selection occurs
There will be more people with the average characteristic and extreme phenotypes will have died after natural selection
What is the correct way to draw a histogram
Bars don’t touch
Bars are different widths
Frequency density= frequency/ category range
Describe the process of antibiotic resistance
A random mutation causes an advantageous allele which makes it resistant to an antibiotic
The bacteria with the mutation are more likely to survive as they do not get destroyed by the antibiotic.
Bacteria asexually reproduce and pass on that allele due to binary fission onto its offspring
This occurs over the many generations and allele frequency increases so bacteria evolve to become resistant to antibiotics
What type of selection is antibiotic resistance?
Antibiotic resistance is directional is the mean has shifted from before and after selection population has become more resistant to antibiotics
Describe the process of binary fission
Bacterial cell organelles duplicate (plasma and circular DNA replicates)
Each copy of plasmids and circular DNA to opposite poles of the cell
The cell wall and membrane pinches cytoplasm splits and cell splits
How do you calculate how many times a bacteria has divided to result in a certain number
log 2 (number of bacteria) x minutes
How do you calculate how many bacteria there are after a certain number of divisions?
Number doubles each time
E.g 15 divisions
2 ^15 = 32,768
What is the zone of inhibition?
Area around an antibiotic on a Petri dish which has destroyed bacteria, leaving a clear circle
What does standard deviation tell us?
Standard deviation helps us know how spread out data is from the mean to work out if it is precise, it also tells us how precise measurements are how reliable measurements are and if two means are significantly different
How do you calculate the size of the zone of inhibition?
Measure the diameter of the circle
Half that number to get the radius
Calculate the area by doing pi R ^2
