1. A2 Biology unit F215 – exam 1hour 45 mins 50% of marks for A2
Population genetics
includes
Hardy Weinberg equations,
natural selection and artificial selection

2. Call for European Cystic Fibrosis healthcare gap to be closed Press release 19 March 2010 by Bristol University
A healthcare gap amounting to a ‘death sentence’ for Cystic Fibrosis (CF) children born in Eastern Europe must be closed say researchers from the EuroCareCF Coordination Action for Cystic Fibrosis.
“We know that this disease occurs randomly in about 1 in 4,000 children born to healthy parents across the EU,” he said.  “Despite this, the team encountered many fewer people with CF in poorer countries.  CF patients there die far younger than in long standing EU countries.”
Understanding the inheritance of characteristics and of population genetics can help governments to plan healthcare.

3. 2 inherited characters in humans – both involve autosomal recessive alleles
Cystic fibrosis – excessive mucus in bronchioles reduces gas exchange + few digestive enzymes from pancreas reach gut
PKU = phenylketonuria – enzyme to convert phenylalanine into tyrosine not present; child has light skin and hair + brain damage (now blood test at birth + special diet)

4. Key definitions page 2
1) A population of a species is:-
a group of organisms which have similar characteristics e.g. anatomy, physiology, biochemistry and behaviour and which can interbreed to produce fertile offspring
2) The gene pool is:-
all the genes in the gametes of a population from which the genotypes or genomes of the next generation are formed

5. Hardy was a British
Mathematician;
Weinberg was a
German doctor

6. The Hardy Weinberg principle predicts that:-
the frequency of an allele in the gene pool will not change from one generation to the next (and so the frequency of genotypes / genomes also remains constant)
this is only true if
the population is very large
there is no immigration or emigration from the population
mating is random
all genotypes are equally fertile
there are no random mutations
Which could be met by a natural population?

7. Hardy Weinberg equations
Allele frequency
frequency of dominant allele = p
frequency of recessive allele = q
total frequency of alleles for a character in the population = 1
p + q = 1
So if r = 0.6 then frequency of R = 0.4

8. Hardy Weinberg equations
p2 = frequency of homozygous dominant genotype
2pq = frequency of heterozygous genotype
q = frequency of homozygous recessive genotype
total frequency of all genotypes in population = 1
p2 + 2pq + q2 = 1
So if frequency rr is 0.39 and RR is 0.34 frequency of Rr = 0.27

9. Tables for Hardy-Weinberg calculations
decimal %
allele p q
decimal %
genotype p2
2pq q2

11. Hardy Weinberg - answers
p = 0.3 and q = 0.7;
Genotype frequencies = 9% 49% 42%
2)a) q = 0.3 or 30% b) 0.49 or 49%
c) 0.42 or 42%
3) q = or 0.8%

12. Hardy Weinberg - answers
4)a) q = 0.42 or 42% b) p = 0.58 or 58%
c) 33% and 49%
5)a) q = 0.07 so p = 0.93
b) 0.49% c) 0.13 or 13%
6)a) q = b) or 1.98%

13. Hardy Weinberg - answers
7) a) q = homozygotes = 0.36 or 36%
heterozygotes = 0.48 or 48%
b) Allele for sickle cell anaemia gives resistance to malaria = an environmental selection pressure
People with allele for normal haemoglobin and for sickle cell haemoglobin have selective advantage where malaria is present so more likely to survive and pass on alleles to offspring
c) If malaria eradicated no advantage to have sickle cell allele
Also need large population, no immigration or emigration, random mating, equal fertility and no mutations

14. Hardy Weinberg - answers
8)a) q = 0.6
Homozygotes = 0.16 or 16%
Heterozygotes = 0.48 or 48%
b) No selective advantage to be tongue roller – remains same if all the conditions of Hardy-Weinberg equation are fulfilled
9)a) no – until very recently people with cystic fibrosis have not reproduced
b) Termination of pregnancies may reduce allele frequencies – but gene may still mutate

15. Genetic drift in small populations p7

16. Genetic drift = effect of chance factors on allele frequency in gene pool

17. Genetic drift in frog-hoppers on the Scilly Islands

18. Genetic drift and frog hoppers
St Agnes + St Mary’s – all striped;
Other islands – striped and melanic but proportions vary;
On all but one island more striped than melanic
2) Small population on island;
may only have genes for striped = founder effect;
Or chance means some genotypes reproduce more than others – large effect on phenotypes as small number of individuals
3) Difficult!
Allow small populations to breed for several generations in lab and record results
In field could investigate environmental factors which might affect breeding e.g. temperature, shelter, camouflage

19. Natural selection – stabilising and directional

20. Speciation – development of a new species
Needs reproductive isolation of a population so individuals cannot interbreed
Alleles do not pass from one gene pool to the other
Allopatric speciation = geographical isolation
Sympatric speciation = behavioural / seasonal isolation

21. Reproductive isolation by courtship behaviour = sympatric

22. Reproductive isolation by time of flowering = sympatric

23. Peppered moths – evolution in action http://www. biologycorner
Which moths survive? Why are the moths
Why? different colours in different areas?

24. The peppered moth Biston betularia Stabilising and directional selection p10

25. Definition of a species p11
Biological definition
Phylogenetic / evolutionary / cladistic definition
Why have 2 definitions?
Are they equally useful?

26. Both select the organisms to reproduce
Artificial selection and natural selection Similarities and differences p13
Both select the organisms to reproduce
Humans choose the characteristics in artificial selection and it usually produces lower genetic diversity in the gene pool
Selection pressures in natural selection are less likely to reduce genetic diversity of the species

27. Artificial selection

28. Selective breeding of cattle

29. Artificial selection – dairy cows

30. Selective breeding = humans select the organisms that will reproduce (this is not genetic engineering)
Choose parents which show the desired characteristic (animals or plants)
e.g. resistance to disease, speed of growth, height, milk yield
Breed the parents
Select the offspring with the desired characteristic
Use them for breeding
Continue for many generations (detailed records needed)
Result - desired features are more obvious but genetic diversity is decreased by the inbreeding

33. Improving food production by selective breeding

34. Recent selective breeding of wheat

35. Producing bread wheat Triticum aestivum by artificial selection

36. Producing bread wheat Triticum aestivum by artificial selection
1) Wild einkorn wheat 2N = 14 chromosomes = AA genome (haploid number = 7)
2) Einkorn wheat – artificial selection of desired characters by early farmers
2N = 14 chromosomes = AA genome
3) Crossed with wild grass 2N = 14 chromosomes = BB genome (happened by chance)
Gametes fusing = A and B genomes
Produced sterile hybrid 14 chromosomes = AB genome (no homologous pairs so meiosis cannot produce gametes)

37. Producing bread wheat Triticum aestivum by artificial selection
4) Random mutation  chromosome number doubles  tetraploid 4N = 28
Emmer wheat has genome AABB
5) Chance cross with goat grass 2N = 14 chromosomes = DD genome
Produced sterile hybrid – gametes fusing are AB and D – meiosis unsuccessful
6) Random mutation  chromosome number doubles  hexaploid 6N = 42
Modern bread wheat Triticum aestivum has genome AABBDD

38. Spartina grass on edge of sea

39. How are these 2 species reproductively isolated?

40. Cloning in animals  whole organism or stem cells (reproductive or non-reproductive cloning) p6 - 8

41. Dolly the Sheep – a product of nuclear transfer

42. Where are the enucleate egg and the surrogate mother?

43. Cloning animals – advantages or disadvantages?
Many animals with desired characters produced
Infertile animals can reproduce
Rare animals conserved
Animals genetically identical
Very labour intensive and needs sterile facilities and highly trained staff
Breeding can occur at any time of year
Genetically modified animals can be used to produce pharmaceutical chemicals