epigenetics

why does HAHS genotype for SCA provide resistance to malaria

plasmodium can’t live or reproduce inside the sickled RBC

what role does natural selection have in changing allele frequencies

increases frequency of advantageous alleles —> changes gene pool

outline natural selection

• variation in population

• individuals have a mutation which provides a selective advantage against a selection pressure

• highest chance of surviving + reproducing

• pass on advantageous alleles over many generations

what are the 3 types of genotype for sickle cell anaemia and what’s their effect on the phenotype

1. HbA HbA = normal

2. HbS HbS = SCA —> Hb sticks together due to reduced solubility

3. HbA HbS = SCA trait —> asymptomatic but affected at high altitude

what other factors (apart from natural selection) affect genetic biodiversity

1. Genetic bottlenecks

2. founder effect

explain genetic bottleneck

• caused by a natural disaster

• changes the proportion of alleles in the surviving population

• survival is due to chance —> some alleles lost -→ reduced genepool -→ reduced genetic diversity

explain founder effect

• small group of individuals break away from original population —> forms new colony

• causes differences in allele frequency

• can be due to migration

explain how the ellis-van creveld syndrome and blood group distribution are linked to founder effect

1. Ellis-van creveld - amish population split + migrated —> isolated —> little genetic diversity —> inbreeding increased frequency of EVC allele

• symptoms = dwarfism, extra fingers, cleft palette

2.blood group distribution - migration caused different blood group types to be more common in certain areas

what assumptions are made in Harvey-Weinberg

1. large population

2. random mating

3. no new mutations

4. no change to allele frequency

5. no migration

6. no natural selection - all genotypes have equal chance of surviving + reproducing

what does p and q represent in harvey-weinberg + what does each part of p² + 2pq + q² = 1 mean?

• p = dominant allele

• q = recessive allele

• p² = homozygous dominant

• 2pq = heterozygous

• q² = homozygous recessive

what factors can change the gene pool?

• genetic drift - frequency of alleles changes randomly over time due to sudden events

• natural selection

• founder effect

• immigration

outline geographical isolation (allopatric speciation)

• physical, geographical barrier separates members of same species

• different mutations arise in each population

• separated populations experience different selection pressures

• Natural selection changes allele frequencies in each population

• if reintroduced, can’t interbreed to form fertile offspring

• 2 new species formed

outline reproductive isolation (sympatric speciation)

• members of same species share same habitat

• but cannot mate

• due to different mating seasons, different mating rituals

• individuals no longer interbreed

what are epigenetic changes

structure of gene remains the same but genes are switched on/off —> gene expression can be increased/decreased

what are the 2 types of epigenetic changes

1. DNA methylation

2. Histone modification

outline DNA methylation as an epigenetic change

• add methyl groups to DNA

• decreases transcription —> decreases gene expression —> decreases production of ppc —> less protein synthesis

• no change to DNA sequence + reversible

outline histone modification

• chemical modification of histone proteins e.g addition of methly/phosphate group

• change how tightly DNA is wound around the histones

• Tightly wound DNA = DNA is less accessible to transcription factors —> reduced transcription

• loosely wound DNA = DNA is more accessible to transcription factors —> increased transcription

outline the norrbotten studies, dutch hunger winter + twin studies as examples of epigenetic studies in humans

1. Norbotten - people in this area experienced years of famine, then years of abundant crops —> descendants of women who experienced famine had foetus’ w lower life expectancies

2. dutch hunger winter - children conceived during famine had inc risk of diabetes, CHD + obesity

3. twin studies - identical twins have same DNA sequence —> any genetic changes due to environmental factors