Populations And Evolution Flashcards
Define gene pool
All the alleles of all the genes of all the individuals in a population at a given time / all the alleles in a population
Define allelic frequency
The number of times an allele occurs within a gene pool
What is the hardy weinberg principle
P squared + 2pq+ q squared = 1 (genotype frequency). Where p squared is homozygous dominant, q squared is homozygous recessive and 2pq is heterozygous. P +q=1 (allele frequency). Start with q squared (convert % in decimal) then square root to find q, find p by 1-q then find 2pq by 2xpxq
What are the assumptions for the hardy Weinberg principle to work
Proportion of dominant and recessive alleles remains same from one gen to next. Only happens if: no mutation, population is isolated so no gene flow in or out, population is large, mating in pop is random and no selection (alleles equally likely to be passed on). Allele freqs can change due to natural selection so hardy wenberh doesn’t apply
Examples when a new allele leads to increased reproductive success
Sickle cell allele more prevalent in areas with malaria as presence of allele is more resistant to malaria and having do dominant version means. There is enough healthy red blood cells to live normally
Define phenotypic variation
The difference in phenotypes between organisms of the same species
How can environment affect variation
Can affect phenotypes e.g sunlight hours, supply of nutrients, availability of water, temp range, 02 levels (abiotic factors affect growth). Example: plant with tall genes may never grow tall if lacking nutrients
Sources of genetic variation
1.Mutation is the primary source, 2. random fertilisation of gametes and 3. crossing over, independent assortment/segregation of homologous chromosomes in meiosis
What is genetic drift
The change in composition of a gene pool (allele and phenotype frequencies) as a result of chance or random events. Occurs faster and more significant in smaller populations, chance events have bigger impact on gene. Pool. Large less affected and maintain more stable allele frequencies. May result in loss of some alleles (including beneficial) and fixation/rise to 100% of others
Define evolution
Changes in allele frequency over time. Can be small scale/micro or large scale/macro (geological time and arise of new species)
What enables natural selection to occur
Genetic diversity is a factor enabling natural selection to occur. Genetic variation that exists within a population is heritable (genetic) and determined by presence of alleles
What are examples of selection pressures and what do they lead to
Predation, disease, intraspecific (competition between different species) competition and interspecific competition (within a species). Lead to differential survival and reproduction. Adaptations lead to differential reproduction in a species, allowing natural selection to occur
What are the principles of natural selection
Genetic variation exists within a population, new alleles arise by mutation. Environmental pressures lead to differential reproductive success in those with advantageous allele (more likely to survive and reproduce, passing alleles onto offspring). Over time, advantageous allele increases in frequency in population
How to find the actual frequency of an allele without hardy Weinberg
Number of alleles there are divided by the total number of alleles
Describe stabilising selection
An intermediate phenotype is favoured at the expense of extremes. Mean, median and mode stay the same but S.d. Decreases. Occurs when environmental conditions are stable. Extremes are selected against and allele freq of intermediate rise (e.g human birth weights)
