Topic 4 Flashcards
What is a gene?
The combination of two alleles
What is an allele?
Variation of a gene on chromosomes. Mom has blue eye allele and dad has brown eye allele
What is genetic variation?
The diversity of alleles in a population. Allele varieties=genetic variation
What is phenotype variation?
Variety in the visible expression of “types”. Is caused by genotype and environment
Where and how does natural selection operate?
Natural selction operates at the phenotype. It operates with the use of environment and genotype
What is statistical variation?
Measures the difference from an average value. So like is a graph line really thin or thicker?
What is evolution?
Change in the frequencies of alleles in a population between generations
What are the five factors that can change allele frequency?
Natural Selection, Sexual selection, mutations, gene flow and genetic drift
What is sexual selection?
It is non random mating and is due to preferred phenotypes. It may decrease genetic variation
What is non-random mating?
Increase or decrease in the probability that a specific individual will mate
What are mutations?
A change in an individuals DNA that can be cause by an error in DNA replication or by structural damage to DNA. It is random, meaning it is unaffected by environment and can be good, bad or neutral
What is Gene Flow?
The transfer of alleles between populations. It increases the variation within a population but decreases the variation between populations
What is genetic drift?
Changes in allele frequency due to chance (regardless of Natural Selection). Allele frequencies “drift” from one generation to the next. The impact of drift is greater on smaller generations. Rare alleles are more likely to be lost due to drift. Examples are founder effect and bottleneck effect
What is the founder effect?
A new population is established by a few colonizers. There is a small fraction of genetic variation compared to the ancestral populations and change in allele frequency
What is the bottleneck effect?
Only a few individuals survive something (natural disaster, etc.) and so these few are the only ones that produce the next generation. Therefore the gene frequency in the next generation is different then previous generation
What are the mehanisms of Natural Selection?
Directional Selection, Disruptive Selection and Stabilizing selection
What is directional selection?
An extreme phenotype is favored because it has highest fitness. Frequency distribution of alleles shifts which can cause the lose of allelic variations and the loss of genetic variation. Loss of genetic variety but same phenotypic variation
Does statistical variation change in direction selection?
Directional selection is a directional shift in the mean of the population. Statistical variation doesn’t change. As in the curve of a graph doesn’t change it just shifts
What is Disruptive Variation?
Two extremes are favored and results in polymorphism. It maintains genetic variation but changes phenotypic variation. So two types of dark butterfly are favored and the light butterfly begins to die off. Creates graphs with 2 extremes. There is a disadvantage to be the average phenotype
What is polymorphism?
2 or more divergent phenotypes
What is stabilizing selection?
The intermediate or common phenotypes are favored, there is selection against extremes which eliminates harmful mutations. The mean of the population stays the same (variation decreases) and there is little or no evolutionary change (maintains genetic variation). Graph becomes thinner
How do you maintain Genetic variation despite natural selection?
Mutation, Recombination, Fertilization, Independent assortment, disruptive selection, gene flow, negative frequency dependent selection and heterozygote advantage
What is negative frequency dependent selection?
The rare genotype has the advantage
What is heterozygote advantage?
Heterozygotes have the advantage over homozygotes. Think sickle cell anemia
Why cant Natural Selection craft perfect organisms?
Selection can only act on existing variations, evolution is limited by historical restraints, adaptions are often compromises and chance, natural selection and environment interact
