24) Population genetics and epigenetics Flashcards
Natural selection increases _ in a population and alters _
the frequency of beneficial alleles
the gene pool
The allele that causes sickle cell anaemia is a _ as produces both positive and negative effects
gene variant
Explain how sickle cell anaemia can cause blockages in capillaries and organ damage
substitution mutation -> abnormal haemoglobin
at low concentrations of oxygen, haemoglobin clumps together and deforms red blood cells into a sickle shape
State the symbols for the co-dominant alleles for normal and abnormal haemoglobin production
H^A and H^S
Why is there a link between the distribution of malaria and the frequency of the H^S allele?
H^S has a protective effect as slightly increases CO2 production during the breakdown of red blood cells and therefore prevents development of the disease
Give the possible genotypes for H^A and H^S
H^A H^A = normal haemoglobin
H^S H^S = sickle cell anaemia (unlikely to survive long enough to reproduce, allele expected decrease)
H^A H^S = sickle cell trait (symptoms only at low O2 levels)
DNA mutation alters the _ of a _ and can therefore, change _ of a _ including _
amino acid sequence polypeptide tertiary structure protein active site of enzymes
What do the alleles H^C and H^H represent?
H^C = breakdown of some red blood cells H^H = high affinity for O2, little released at tissues
Define genetic bottleneck
a drastic reduction in population number, with an accompanying reduction in genetic diversity, where survival is often due to chance
Define founder effect
a type of genetic bottleneck in which a group of organisms leave an original population to form a new smaller population / colony
Describe Ellis-van Crevald syndrome
recessive allele more common in Amish that has symptoms of polydactyly, dwarfism, short ribs and cleft palates
Describe blood group distribution
ABO, human migration / each new population has the potential to filter the gene pool and proportion of each allele present
Define the Hardy-Weinberg principle
the proportion of alleles will remain the same from one generation to the next provided... no new mutations no migration (flow of alleles) no natural selection for/against alleles large population random mating
Give two equations relating to the Hardy-Weinberg principle for genes with two variants (one recessive, one dominant)
p + q = 1
p = frequency of dominant allele; q = frequency of recessive allele
p^2 + 2pq + q^2 = 1
p^2 = frequency of homozygous dominant genotype; 2pq = frequency of heterozygous genotype; q^2 = frequency of homozygous recessive genotype
Define speciation
the formation of new species (when groups of individuals of the same species evolve in different ways due to a form of isolation; gene flow has effectively stopped between populations
Outline how speciation by geographical isolation takes place (8 steps)
- population becomes isolated geographically (how)
- different environmental conditions (name)
- different selection pressures (examples)
- mutations occur in the population leading to different phenotypes/advantageous alleles in population
- phenotype gives a survival advantage
- organisms more likely to survive to breed and pass on advantageous alleles
- advantageous allele increases in gene pool
- over time (many generations) become genetically different and unable to interbreed to produce fertile offspring
Define geographical isolation
when a physical barrier separates members of a species
When does reproductive isolation arise?
eventually in geographically isolated populations or between organisms whose geographically distributions overlap by isolation mechanisms / barriers
Name 3 isolation mechanisms / barriers which could result in reproductive isolation
temporal - different mating seasons among animals / flowering seasons in plants
behavioural - different mating rituals
mechanical / anatomical - incompatible reproductive systems
As well as isolation mechanisms / barriers which could result in reproductive isolation, what could stop successful reproduction?
post-mating barriers e.g. gametes being unable to meet or hybrid offspring being sterile
Define epigenetics
the study of changes to gene expression without changing the genetic code (non-mutational changes)
How can gene expression change without changing the genetic code?
genes can be switched ‘on’ or ‘off’, the extent to which they are expressed is altered (inherited/influenced by environment)
DNA methylation
histone modification
Explain how DNA methylation can result in changes to gene expression
methyl group (-CH3) added to cytosine bases of DNA reducing gene expression by preventing transcription
Explain how histone modification can result in changes to gene expression
histones can be chemically modified (addition of an acetyl, methyl or phosphate group) to activate or deactivate a gene - making it more or less accessible to transcription factors
Define histones
proteins in eukaryotes that the DNA wrap around in supercoiling
Give 3 conditions of a gene switched on
unmethylated cytosine
acetylated histones
transcription occurs
Give 3 conditions of a gene switched off
methylated cytosine
deacetylated histones
transcription does not occur
Norrbotten studies observed years of famine and abundance which led to women with reduced life expectancies as foetuses. Also, descendants of men over-nourished during puberty (sperm-forming) had reduced life expectancies. What was the conclusion made?
environment can produce epigenetic changes that are passed on to subsequent generations
Dutch Hunger Winter studies observed wartime winter famine and malnourishment of mothers during early pregnancy. Children conceived and grandchildren had a higher risk of diabetes, obesity and heart disease. What was the conclusion made?
epigenetic alterations to genes associated with these diseases is perhaps the reason for health problems (regardless of environment in early lives)
Twin studies observed identical twins separated early I life and raised in different environments. Significant differences in middle age and those who spent less of their lifetime together showed the greatest epigenetic changes. What conclusion was made?
the influence on genetic and environmental factors on phenotypes
Name 3 diseases caused by a substitution mutation
sickle cell anaemia
cystic fibrosis
PKU
Suggest why a substitution mutation on a DNA molecule changing a triplet from AGA to AGG did not result in a genetic disease
genetic code is degenerate
similar R group therefore, doesn’t change tertiary structure
codes for the same amino acid
some amino acids have more than one triplet
Changes to the p53 gene have been associated with many different types of cancer. Suggest whether the p53 gene is activated or inactivated when a cell becomes cancerous and explain why.
inactivated because... tumour-suppressor gene failure of DNA repair cell cycle not stopped at check points apoptosis not initiated
An anticancer vaccine would lead to the production of antibody molecules that recognise Tumour Associated Antigens in the host. Explain how the structure of the antibody molecule would enable it to recognise only TAAs.
variable region complementary to antigen
different antigens would have different 3D shapes
Explain why the blue-headed wrasse and the rainbow wrasse are described as different species
different phenotypes
different mating behaviour
unable to reproduce to make fertile offspring
