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Summary Genetics, populations, evolution and ecosystems notes
Notes and answers based around key questions and mark points for the mark scheme Used these notes to receive an A* as they are tailored to the mark points
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Sunday, 4 September yGenetics, Populations, Evolution & Ecosystems
Inheritance
How to tell whether a condition is …. from a family tree
Dominant
- if an affected parent has children with an unaffected parent, half the children will be af-
fected
Recessive
- no recessive phenotypes in parents but recessive offspring (parents are heterozy-
gous)
Sex linked
- all the sons/daughters of an affected parent are affected
Co dominance
- symbols =
Linkage
- alleles found on the same chromosome are more likely to be displayed together
- Crossing over may occur to produce other gametes but there will be fewer of these in-
dividuals
Why are ratios of alleles not the same as expected
- fertilisation of gametes is random
- the sample size may be too small
- the genes may be linked
- epistasis may be occurring
- offspring phenotypes are a probability
Determining sex
- males = XY, females = XX
- Y is shorter and smaller than X
How can a recessive child be produced from a parents that aren't carriers
- random mutation occurred
- in the gene being researched
1
, Sunday, 4 September y
- causing a change in amino acid sequence
Chi squared
- used with categorical data
Null hypothesis
- there is no significant difference between observed and expected
- can be confirmed if the chi squared value is less than the critical value (to the degrees
of freedom 1 less than the amount of groups tested)
Significance
e.g. difference is significant to the 0.05 level
- probability of 0.95 that the difference is not due to chance
Experiments
Why is it advantageous to use small islands for genetic investigations
- all individuals can be sampled - less sampling error
- there is little gene flow
- there may be different selection pressures elsewhere
Populations
Gene pool
- all the different alleles of genes in a population
Classification
Why is accurate classification of organism important
- It ensures scientists can communicate clearly when discussing organsims
- allows scientists to better understand evolution of species
- ensures small subspecies aren't left to go extinct
Why may two groups be defined as different populations
- no interbreeding
- They may not live in the same habitat
Calculations
Hardy-weinberg
2
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