19: Population Genetics Flashcards
Define Variation:
What can Intraspecific Variation lead to?
- the difference in characteristics or phenotypes that exist
- occurs between same species, so it could potentially lead to natural selection an eventually speciation
Why do some characteristics in a population fall into limited number of distinct forms?
- this is due to genetic factors only, where few genes act
- examples of this are tongue rollers and blood group which cannot be adjusted via environment
Name some environmental/genetic factors of variation:
Genetic:
- diet
- disease
- climate
Environment:
- mutation
- meiosis
- random fusion of gametes
What is the only way asexually reproducing organisms show variation?
mutation
What are 3 sources of genetic variation?
- meiosis: formation of gametes
- this is caused via crossing over and independent segregation, which is a major source of intraspecific variation - random fertilisation of gametes:
- when gametes fuse, and the egg is fertilised, it’s a completely random process, which creates a large variation within a species, as each individual has different characteristics - mutation: change in the amount/structure of the DNA of an organism
These all produce a change in the characteristics of the organism which can be passed onto cells
Explain how gene mutations can lead to production of non-functioning proteins:
- a gene is the sequence of bases in DNA that codes for the production of a protein
- if the base sequence is altered, this leads to a change in the base sequence of mRNA transcribed
- this leads to a change in the sequence of amino acids coded for in translation
- this change in the primary structure of the protein causes a change in tertiary structure, as hydrogen bonds/ionic/disulfide bonds break and reform in different places
- leading to a change in the unique active site shape, so substrate no longer complementary
- this leads to a loss in function of the protein
How can mutation rates be altered?
What are these factors called?
- they may increase if:
- there is use of carcinogens
- there is high energy ionising radiation e.g UV light - mutagenic agents
Define Population:
Define Gene Pool:
- all of the individuals of one species in a habitat or ecosystem
- the sum total of all the alleles of all the gene loci in a population at a particular time
Describe 3 other types of Mutation:
(Paper 3)
- Duplication of Bases:
- one or more of the bases are repeated, => this leads to frame-shift - Inversion of Bases:
- a group of bases becomes separated from the DNA sequence, and rejoin at the same position but in inverse order - Translocation of Bases:
- a group of bases becomes separated from the DNA sequence on one chromosome, and become inserted into the DNA sequence of the same or a different chromosome
What are the types of Mutation?
(Paper 1)
- Addition/Deletion:
- an extra base is removed/added to this sequence
- this changes all triplets after the mutation, therefore a completely different amino acid sequence is made
- this is called “frame-shift” - Substitution:
- one base is swapped for another
2i) mis-sense: one of the amino acids in the polypeptide could change, altering primary structure => therefore altering tertiary structure => final shape of active site
2ii) nonsense: the base change could result in the formation of a stop codon, marking the end of translation
2iii) silent: it could cause no difference due to the DEGENERATE nature the genetic code
Hardy-Weinberg Equations:
p + q = 1
p^2 2pq + q^2 = 1
p = frequency of dominant allele
q = frequency of recessive allele
p^2 = frequency of homozygous dominant
q^2 = frequency of homozygous recessive
2pq = frequency of heterozygous genotype
What is the Hardy-Weinberg Principle?
- frequencies of the allele of a particular gene in a population will stay constant from generation to generation, under certain conditions
What are the certain conditions for which the Hardy-Weinberg Principle is correct?
- population must be large
- mating between individuals must be random
- no mutations
- all genotypes must be equally likely to reproduce
- no immmigration/emmigration
What does the fact that the Hardy-Weinberg principle never occurs?
- shows that species are constantly in a state of evolutionary flux, and it is possible to see to what extent this occurs by seeing how great the deviations are
What is Genetic Drift?
Give an example to how this can occur?
- basically the idea that allele frequencies can change simply due to chance
- in a small population, these chance events have a greater likelihood, whilst in a large population these factors of chance are more likely to even out
