Flashcards in Evolution- The Evolution of Population Deck (30)
What are the 3 mechanisms that cause allele frequency change?
1. Natural selection
2. Genetic drift
3. Gene flow
What is the difference between genetic variation and phenotypic variation?
Genetic- variation in individual genotype leads to variation in individual phenotype.
Phenotypic- occurs between individuals in populations of all species
What are the two types or variation?
1. Discrete which is the either-or traits(pink or red)
2. Quantitative which are the continuum traits(height or length)
How do geneticists measure genetic variation?
Quantifying heterozygosity at the gene level and the molecular level
What is a mutation?
Changes in the nucleotide sequence that cause new genes and alleles to rise
What is the difference between point mutation and base-pair substitution?
Point mutation changes one base pair in a gene and can cause significant change in phenotype but is usually harmless.
Base-pair substitution changes a gene number/sequence and affects many loci at once. It is usually harmful
What can low mutation rates lead to?
Population change especially with fast generation time and large population
What is sexual recombination?
The gametes vary between individuals because of independent assortment and crossing over
What is the definition of populations?
Groups of individuals of the same species that live in the same place that are capable of interbreeding and producing fertile offspring
What is a gene pool?
All of the alleles for all loci in a population. Mating draws two alleles from the pool at random
STUDY CALCULATING ALLELE FREQUENCIES
What is the Hardy-Weinberg Theorm?
-It describes a hypothetic population that is not evolving at a particular locus
-Frequencies of alleles in the gene pool remain constant over generations IF only Mendelian segregation and recombination of allele are at work
EQUATION AND FREQUENCIES
What are the five H-W assumptions?(must hold for non-evolving populations)
1. No mutations
2. Random mating
3. No natural selection
4. Extremely large population size
5. No gene flow
What is natural selection?
Differential reproductive success. Some alleles are passed to the next generation in greater proportion than others. It accumulates and maintains favourable genotypes in a population
What is genetic drift?
-In stats, the smaller the sample, the greater the chance of deviation from a predicted result
-Changes in gene pool of population due to chance
-Allele frequencies can fluctuate unpredictably which tends to reduce genetic variation
What is the bottleneck effect?
A sudden environmental change drastically reduces the population size. The gene pool of the surviving population might not reflect the gene pool of the original population
What are the effects of genetic drift? (4)
1. Significant in small populations
2. Causes allele frequencies to change at random
3. Lead to a loss of genetic variation within populations
4. Cause harmful alleles to become fixed
What is gene flow?
Results in a gain or loss of allele due to the movement of fertile individuals or gametes. It tends to reduce differences between populations over time
What is relative fitness?
The contribution of an individual to the gene pool of the next generation relative to alternative genotypes for the same locus
What are the 3 modes of selection?
What is directional selection?
Favours individuals at one end of phenotypic range
What is disruptive selection?
Favours individuals at either extreme of phenotypic range
What is stabilising selection?
Favours individuals in the middle of phenotypic range
What can sexual selection cause?
- Massive sexual dimorphism
- Cause differences between sexes and secondary sexual characteristics
What is intra-sexual selection?
Within sex competition for mates. Individuals of one sex choose the other
What is diploidy?
It preserves variation as hidden recessive alleles
What is the heterozygote advantage?
- Higher fitness in heterozygous individuals
- Natural selection will tend to maintain 2+ ales at that locus
What is natural variation?
Genetic variation that appears to result in no selection advantage