Chapter 6 Flashcards
Given that mutations are rare in populations, how does a mutation spread through a population and become common?
If the mutation confers a selective advantage, it will spread through the population because it increases individual fitness. Because mutations produce dominant alleles, they spread rapidly through the population by masking recessive alleles. Mutations increase the frequency of crossing over during meiosis, producing more chromosomes that are carrying the mutation. As the population grows larger, the chance that the same allele will mutate in the sex cells of multiple individuals increases.
Compare and contrast genetic variation caused by random assortment versus recombination.
The chromosomes in a haploid gamete are a random assortment of the chromosomes in the parent’s diploid cells, meaning that they can be any combination of chromosomes that the parent received from its mother and father. When an individual produces an egg cell, for example, some chromosomes in the egg will have come from the individual’s father, whereas other chromosomes in the egg will have come from the individual’s mother.
A second way that genetic variation can arise is through genetic recombination, which is the reshuffling of genes that can occur as DNA is copied during meiosis, the process that creates haploid gametes from diploid parent cells. During meiosis, pairs of homologous chromosomes — one member of which is inherited from each parent — line up next to each other. When the two chromosomes in the pair do not exchange any DNA, we end up with haploid cells that contain unaltered chromosomes. However, sometimes the two chromosomes in the pair do exchange DNA, in a process known as crossing over. In some cases, crossing over can also occur between nonhomologous chromosomes. In either case, new genes are not being created, but new combinations of alleles are produced that have the potential to produce new phenotypes.
The insecticide DDT has been widely used to control the mosquitoes that carry malaria. How would you explain the fact that many mosquito populations are now resistant to DDT?
Mosquito populations are resistant to DDT because there could have been a mutation in their gene which made them resistant to the DDT. these mosquitos that had resistance lived on, spread their gene and had more offspring. DDT becomes ineffective so quickly now because DDT-resistant mosquitoes exist at low frequency in the global mosquito population and, when a local population is sprayed, a strong force of selection in favor of the resistant mosquitoes is immediately created. It is only a matter of time before the resistant mosquitoes take over.
How does the introduction of new individuals to a population help offset problems associated with genetic drift?
Genetic drift occurs when genetic variation is lost due to random variation in mating, mortality, fecundity, or inheritance. Genetic drift is more common in small populations because random events can have a disproportionately large effect on the frequencies of genes in the population. Adding new individuals will introduce more alleles into the population to increase genetic diversity. Without new individuals, a bottleneck effect will happen in which A reduction of genetic diversity in a population due to a large reduction in population size. Cheetahs are an example of a species with a bottleneck effect. This low genetic variation makes cheetahs more vulnerable to pathogens, including a deadly pathogen that causes the disorder known as AA amyloidosis, which kills up to 70 percent of cheetahs held in captivity.
Compare and contrast evolution by artificial selection with evolution by natural selection.
-The main difference between natural and artificial selection is that natural selection produces a great biological diversity whereas artificial selection produces varieties of organisms such as improved crops and livestock.
-Natural selection is a process by whereby organisms better adapted to their environment tend to survive and produce more offspring. Natural selection facilitates evolution through genetic diversity. Slow process. Natural populations used.
-Artificial selection is a process by which animals and plants are chosen by a breeder for desirable traits. Artificial does not facilitate evolution. Rapid process. Domestic populations used.
How does the breeding of domesticated animals provide evidence for the power of evolution on diverse phenotypes?
- Humans breed animals for desired characteristics , due to selective breeding more phenotypes are introduced
- Introduces new phenotypes people desire, survive and reproduce for many generations increasing genetic variation
How is it that polyploidy can allow us to observe the evolution of a new species within one generation?
Polyploidy is when a species contains three or more sets of chromosomes. It allows us to observe the evolution of a new species within one generation because when a polyploid is formed, it instantly becomes a species that is genetically distinct from its parents. Several species of insects, snails, and salamanders are naturally polyploid, as are 15 percent of all flowering plant species.
chromosomes fail to separate properly during mitosis or meiosis. In the case of gametes formed by meiosis, the result is that the gametes are diploid rather than haploid. If a diploid egg is subsequently fertilized by a haploid sperm, the resulting zygote will contain three sets of chromosomes.
Distinguish between microevolution and macroevolution.
Microevolution happens on a small scale (within a single population), while macroevolution happens on a scale that transcends the boundaries of a single species. Ex. dogs being different kinds (microevolution). Macroevolution large -scale across many species and not always directly observable. Chimp to humans lol. Takes many years while micro is quicker. Macro is not directly observable and we need fossil evidence.
what is the difference between the processes involved in allopatric speciation and sympatric speciation?
Allopatric speciation: when a species separates into two separate groups which are isolated from one another. A physical barrier, such as a mountain range or a waterway, makes it impossible for them to breed with one another. Land was once one then separated into 2 making it impossible to get to the other side.
Sympatric speciation: gives rise to new species without geographic isolation
In allopatric speciation, groups from an ancestral population evolve into separate species due to a period of geographical separation. In sympatric speciation, groups from the same ancestral population evolve into separate species without any geographical separation
Compare and contrast stabilizing, directional, and disruptive selection with regard to how each affects the mean phenotype of the population as well as the variance in the phenotype
Stabilizing selection: When individuals with intermediate phenotypes have higher survival and reproductive success than those with extreme phenotypes.
Directional selection: When individuals with an extreme phenotype experience higher fitness than the average phenotype of the population.
Disruptive selection:When individuals with either extreme phenotype experience higher fitness than individuals with an intermediate phenotype.
