Evolution Flashcards
what is a gene pool?
the complete range of alleles present in a population
what is allele frequency?
how often an allele occurs in a population
list the steps of evolution by natural selection
new alleles generated by mutations in genes
selection pressure creates a struggle for survival
some are better adapted to the selection pressures than others
individuals that have an allele that increases their chance of survival are more likely to survive, reproduce and pass on the advantageous allele
a greater proportion of the next-generation inherit the advantageous allele
more likely to pass on and the frequency of advantageous allele increases from generation to generation
What is stabilising selection?
When the environment isn’t changing much individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce
it reduces the range of possible phenotypes
what is directional selection?
when there’s a change in the environment individuals of alleles for characteristics of an extreme type are more likely to survive and reproduce
what is genetic drift?
instead of environmental factors affecting which individuals survive, breed and pass on their alleles, chance dictate which alleles are passed on
evolution by genetic drift usually has a greater effect in smaller populations where chance has a greater influence
in larger populations any chance variations in allele frequency tend to even out across the whole population
how does genetic drift work?
individuals within a population show variation in their genotypes
by chance, the allele for one genotype is passed onto the offspring more often than others
so the number of individuals with the allele increases
if by chance the same allele was passed on more often again and again it can lead to evolution as the allele becomes more common in the population
what are genetic bottlenecks?
its an event that causes a big reduction in a population size leading to a reduction in the gene pool
evolution by genetic drift has a greater effect if there’s a genetic bottleneck
what is the founder effect?
it describes what happens when just a few organisms from a population start a new population and there are only a small number of different alleles in the initial gene pool
how does the founder effect work?
individuals within a population show variation in their genotypes
some of these individuals start a new population
by chance, these individuals mostly have one particular genotype
without any further ‘gene flow’ the new population will grow with reduced genetic variation
as the population is small it’s more heavily influenced by genetic drift than a larger population
give examples of when the founder effect can occur?
it can occur as a result of migration leading to geographical separation or a new colony being separated from the original population for another reason such as religion
what is the Hardy-Weinberg principle?
model which predicts that the frequencies of alleles in a population won’t change from one generation to the next, but this prediction is only true under certain conditions: it has to be a large population where there’s no immigration, emigration, mutations or natural selection
there needs to be random mating- all possible genotypes can breed with others
What is artificial selection?
when humans select individuals in a population to breed together to get desirable traits
what are examples of artificial selection?
modern dairy cattle: farmers select a female with a very high milk yield and a male whose mother had a very high milk yield and breed these two together
they select the offspring with the highest milk yields and breed them together
this is continued over several generations until a very high milk yielding cow is produced
other characteristics selected could be high milk quality, long lactation period, large udders
the same can be done with bread wheat
how have modern techniques made artificial selection easier?
artificial insemination and IVF give farmers more control over which cows reproduce
animal cloning allows farmers to produce genetically identical copies of their best cows
techniques such as plant cloning can be useful in the artificial selection of crop plants
