How to Answer Hardy-Weinberg Questions - A-level Biology - with question pack
How to understand and answer Hardy-Weinberg Questions - A-level Biology. Remember to look out for questions where they give you a dominant phenotype frequency -for instance Huntingdons disease, where the frequency of the sufferers is 1 in 100000 - therefore q squared (recessive allele phenotype) is 99999 in 100000.
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Had a request for some Hardy Weinberg Questions.
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Remember to look out for questions where they give you a dominant phenotype frequency -for instance Huntingdons disease, where the frequency of the sufferers is 1 in 100000 - therefore q squared (recessive allele phenotype) is 99999 in 100000.
Also if they ask you to calculate allele frequency without HW - then all individuals in a population have 2 alleles of each gene. In a population of 600 rats there are 1200 alleles in total.
If 400 are AA, 100 are Aa, and 100 are aa then the frequency of a is (100+200)/1200 = 0.25.
Remember that the HW depends on some very unlikely assumptions !
Assumption 1: No Genetic Drift
Sexual reproduction recombines genetic information in a random pattern. In a small population, it is possible that few individuals carry an allele and simple chance could make them more or less successful in passing on that allele. This is known as genetic drift, and the Hardy-Weinberg assumes that it does not happen. In practical terms, a population at Hardy-Weinberg equilibrium has to be large enough that the frequency of an allele is not impacted by random events.
Assumption 2: A Closed Population
Emigration and immigration -- that is, transfer of individuals into and out of a population -- can change the frequency of alleles. Emigrating individuals might take more of one allele out of a population, and immigrating individuals might come from a population with a different proportion of alleles. This is known as genetic flow, and it is common for most populations, with notable exceptions such as remote islands, deep caves or mountaintops. A population at Hardy-Weinberg equilibrium is assumed to have no genetic flow, or to be a completely closed population.
Assumption 3: Mutations Don’t Happen
Mutations are errors that happen when DNA is being copied. They can be nonsense or neutral, they can be harmful to the organism or they can change the organism in a way that makes them better able to survive and reproduce. Hardy-Weinberg equilibrium assumes that mutations don’t exist because they represent genetic change that is not due to the recombination of existing alleles.
Assumption 4: Random Mating Patterns
The Hardy-Weinberg principle assumes that every individual in a population has an equal chance of mating with every other individual, totally random mating. In a population at Hardy-Weinberg equilibrium, nobody gets to be picky. Random mating, also known as a panmictic population, almost never happens in real life.
Assumption 5: No Natural Selection
Natural selection is a pressure that favors one allele over another because the resulting trait, or phenotype, gives the individual an advantage. From a genetic standpoint, the only advantage that matters is one that helps the individual survive or reproduce more effectively. In a population at Hardy-Weinberg equilibrium, there are assumed to be no evolutionary pressures.
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How to approach and answer A-level Biology Questions that need you to Analyse Figures, Tables and Images - lots of example past paper questions
How to approach and answer A-level Biology Questions that need you to Analyse Figures, Tables and Images - lots of example past paper questions with the markschemes
DO NOT LOOK at the question and then look at the data to answer the question.
Look closely at the graph or table
look very carefully at the axes - have they plotted mean or rate or time, mass/volume or concentration ?
can you see range bars ?
In a table what range is in the replicates when you compare to the mean ?
what trends can you observe ? then think about what principle of biology is being shown by the the trends.
How would you explain the highest value, the lowest value, the point at which the line crosses the x axis, how would you explain the largest range, how would you change the experiment to reduce the spread in the data ?
Once you have a coherent understanding of the trends - only then look at the question.
DO NOT LOOK at the question and then look at the data to answer the question.
ALWAYS LOOK AT THE DATA FIRST
Look closely at the graph or table
Graph look very carefully at the axes - have they plotted rate or time, mass/volume or concentration ? Often students assume enzyme graphs have rate on the y axis - sometimes they don’t !
Table - is the IV in the first column ? What are the units of the DV ? Has a mean been calculated ? Is the data in each row consistent ?
are there range/SD bars on the graph ? remember this indicates the variation in the data that was used to calculate the mean
do the range bars or standard deviation bars overlap ?
In a table what range is in the replicates when you compare to the mean ?
what trends can you observe ? then think about what principle of biology is being shown by the the trends.
How would you explain the highest value, the lowest value, the point at which the line crosses the x axis, how would you explain the largest range, how would you change the method to reduce the spread in the data ?
Once you have a coherent understanding of the trends - only then look at the question.
try this - about 20 questions with data and analysis
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Precise but not accurate ? Language of Measurement - crucial for Biology Practical Exam Questions
Precision, control variables, independent variables ? Confusing for many students, however, particularly important now that this year practical skills are assessed in the exam paper.
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Precision, control variables, independent variables ? Confusing for many students, however, particularly important now that this year practical skills are assessed in the exam paper.
An extremely useful document is the Language of Measurement. Reading it is a great start to improving your approach to practical questions. Below are 3 pages.
Original PDF - is here