9A
There are 3 black sheep and 7 white sheep. What is the allele frequencies for wool colour?
Black allele - 30%
White allele - 70%
Define 'bottleneck effect'
The bottleneck effect occurs when a large portion of a population is wiped out by a random event, such as a natural disaster
Variation, selection pressure, selective advantage, heritability
What is the selection pressure that creates 'superbugs'?
Exposure to antibiotics
State the difference between a silent and a missense mutation
Silent mutations do not change the amino acid coded, while missense mutations do
What is the key difference between genetic drift and gene flow?
Genetic drift is random, gene flow is not
How do scientists know that two populations have speciated?
They can no longer produce viable, fertile offspring when they breed
What is the difference between natural selection and selective breeding?
Human preferences act as the selection pressure instead of random environmental factors
What is aneuploidy? Provide an example.
A chromosomal abnormality which results in the wrong number of chromosomes. e.g. down syndrome has one extra chromosome
Explain how interbreeding affects genetic diversity of a population
Interbreeding can introduce new alleles into a population, increasing genetic diversity
Allopatric speciation is when a population is separated by a physical barrier, creating new pressures e.g. a mountain range forming. Sympatric speciation is when a population speciates in the same environment with different pressures e.g. pH of soil for trees
What is the difference between antigenic drift and antigenic shift?
Antigenic drift is the gradual change of antigens on the surface of viruses, whereas antigenic shift is a sudden change in surface antigens
Why are frameshift mutations more severe than point mutations?
Frameshift mutations are the addition of deletion of a nucleotide, which shifts the entire codon reading frame and all amino acids past that point, significantly affecting protein structure
Explain the difference between immigration and emigration on the genetic diversity of the ORIGINAL population
Immigration is when new individuals enter the population, bringing new alleles and increasing genetic diversity. Emigration is when individuals leave the population, removing alleles and decreasing genetic diversity
What can be a disadvantage of successful natural selection in a population?
If certain traits are selected for, it may decrease the genetic diversity of the population, meaning they are less likely to survive any new pressures.
Provide two human-induced reasons for antibiotic resistance
Not finishing antibiotic treatments, using antibiotics when you do not need to, widespread prescription by doctors
What is a 'block mutation' and in what process do these usually occur?
It is when segments of DNA are deleted, duplicated or rearranged on the chromosome. This happens during meiosis
Why are smaller populations more susceptible to extinction?
Smaller populations typically have less genetic variation. If genetic drift occurs, they may not have the diversity to survive their environment
You are given a 4-mark question asking to explain how natural selection occurred in Darwin's finches. Answer it!
The finches living on the islands had natural genetic variation, including variation in alleles that coded for beak type (1). As the birds lived on different islands, they were exposed to different food sources, which acted as a selection pressure (1). Birds that had beaks that were suited to the food on the island had the selective advantage and were more likely to survive (1) and therefore pass on their alleles to the next generation and change the traits of the population (1)
Explain why a new flu vaccine is required every year
The flu virus undergoes antigenic drift, where the antigens on the surface slightly change each year. This means our memory cells will not recognise it, and a new vaccine is required