Chapter 10 - Variation and Evolution. Flashcards
Why do organisms differ in their phenotypes?
- They have a different genotype.
- They have different environments.
What does it mean if a characteristic is heritable?
If they result from different DNA nucleotide sequences or, in some cases, different epigenetic modification, they can be inherited.
How does sexual reproduction generate heritable variation?
- Crossing over between homologous chromosomes during prophase I of meiosis.
- The random distribution of chromosomes during metaphase I.
- The random distribution of chromatids at metaphase II.
- The mixing of 2 different parental genotypes at fertilisation.
What does it mean if a variation is non-heritable?
If the variation is imposed by the environment that isn’t a result of epigenetic change and cannot be transmitted to offspring.
What are the 2 types of variation?
- Discontinuous.
- Continuous.
What is discontinuous variation?
For some characteristics, there is only a small number of possibilities. There are no intermediates and the characteristics are discrete. These characteristics are controlled by single genes and so are monogenic.
What is continuous variation?
-For some characteristics, there are many possible values e.g. height. The values show a gradation from one extreme to another. These are controlled by many genes and are described as polygenic. The environment has considerable influence on the phenotypes.
What are the 2 types of competition?
- Inter specific competition, between individuals of different species.
- Intra specific competition, between individuals of the same species.
What is selection pressure?
An environmental factor that can alter the frequency of alleles in a population, when it’s limiting.
What is the gene pool?
All the alleles present in a population at a given time.
What is the allele frequency?
The frequency of an allele is its proportion, fraction or percentage of all the alleles of that gene in a gene pool.
What is genetic drift?
Chance variations in allele frequencies in a population.
What are the three factors which can cause significant changes to the allele frequency of a gene pool?
- Mutation.
- Natural selection.
- Genetic drift.
What does the Hardy-Weinberg principle state?
That in ideal conditions, allele and genotype frequencies in a population are constant from generation to generation.
What is meant by the term evolution?
Allele frequencies change and phenotypes alter over time.
What is speciation?
The formation of a new species. If the change in phenotype is profound enough, organisms with the altered phenotype are unable to reproduce successfully with the initial population.
What is the founder effect?
The loss of genetic variation in a new population established by a very small number of individuals from a larger population.
What are the 3 types of natural selection?
- Stabilising selection.
- Directional selection.
- Disruptive selection.
What is the concept of stabilising selection?
In a stable environment, the average phenotype may provide a greater advantage than either extreme. In this case, the extreme values will be selected against.
What is the concept of directional selection?
In a changing environment, an extreme phenotype may become advantageous. Then, other values are selected against and over time, the average phenotype changes.
What is the concept of disruptive selection?
In some situations, the average phenotype doesn’t provide an advantage and is selected against (The extremes are selected for at the same time). If these two demes are isolated, a new species may occur.
What is a species?
A group of phenotypically similar organisms that can interbreed to produce fertile offspring.
What is reproductive isolation?
The prevention of reproduction and, therefore, gene flow between breeding groups within a species.
What are the 2 forms of reproductive isolation?
- Pre-zygotic, gametes are prevented from fusing so a zygote is never formed.
- Post-zygotic, gametes fuse and zygote forms but is sterile and so the genes of the parent species are kept separate.
