Patterns Of Inheritance And Variation Flashcards
What is a gene pool
Sum of all the genes in a population at any given time
What is allele frequency
The relative frequency of a particular allele in a population
What is the frequency of alleles in a population down to?
Evolution
Factors that affect evolution
- mutation: forms new alleles leading to genetic variation
- sexual selection: increases frequency of alleles that code for advantageous characteristics increasing reproductive success
- gene flow: movement of alleles between populations (immigration and emigration)
- generic drift: occurs in small populations. This is a change in allele frequency due to random nature of mutation. This will have a bigger effect in smaller populations than in larger ones
- natural selection: leads to an increase in the number of individuals that have advantageous characteristics as they survive more easily.
What can large populations do due to their large gene pool
Adapt over time due to the presence of many different alleles and genes
What’s the problems with small population with limited genetic diversity?
They can’t adapt and change as easily and More likely to extinct. A new strain of pathogen could wipe a whole population.
What two factors affect the size of a population
Density dependent factors are dependent on population size such as competition, predation, disease…
Density independent factors - affect populations of all sizes in the same way, including climate change, natural disasters, seasons and human activity like deforestation
What are population bottlenecks
Large reductions in population size which last for at least one generation - gene pool hella reduced along with genetic diversity. For example northern elephant seals were almost hunted to extinction in the 19 century with about 20 left. They now have a population of 30 000 but much less genetic variety
What is the founder effect
When small populations can arise due to the establishment of new colonies by a few isolated individuals leading to the founder effect. These populations have much smaller gene pools than the original population.
What is stabilising selection
The norm is selected for and the extremes are selected against, so the frequency of extreme alleles decreases
What is directional selection
This occurs when there is a change in the environment and the normal phenotype is no longer the most advantageous. Organism with the less common and more extreme phenotypes are positively selected. The allele frequency shifts towards extreme phenotypes and evolution occurs. I.e. the peppered moths during the industrial rev
What is disruptive selection
The extremes are selected for and the norm selected against. I.e. the finches observed from Darwin were subjected to disruptive selection. This is opposite to stabilising selection
What is speciation?
The formation of new species through the process of evolution
Why may speciation occur
Members of a population become isolated and no longer interbreed with the rest if the population resulting in no gene flow between the two groups
Alleles within the groups continue to undergo random mutations. The environment of each group may be different or change so different characteristics will be selected for or against
The accumulation of mutations and changes in allele frequencies over many generations eventually lead to large changes in phenotype. The members of the different populations become so different that they are no longer able to interbreed and produce fertile offspring
What is allopatric speciation
This is the more common form of speciation and happens when some members of a population are separated from the rest of the group by a physical barrier such as a river or sea - they become geographically isolated. The diff environments will often be different and will have different selection pressures resulting in different physical adaptations. Because of the small gene pool to begin with it further enhances the differences between the populations.
