frequency-dependent selection

Examples of frequency-dependent selection in the following topics:

• Frequency-Dependent Selection

  • In frequency-dependent selection, phenotypes that are either common or rare are favored through natural selection.
  • Another type of selection, called frequency-dependent selection, favors phenotypes that are either common (positive frequency-dependent selection) or rare (negative frequency-dependent selection).
  • Negative frequency-dependent selection serves to increase the population's genetic variance by selecting for rare phenotypes, whereas positive frequency-dependent selection usually decreases genetic variance by selecting for common phenotypes.
  • Positive frequency-dependent selection reinforces the common phenotype because predators avoid the distinct coloration.
  • Frequency-dependent selection allows for both common and rare phenotypes of the population to appear in a frequency-aided cycle.

• Natural Selection and Adaptive Evolution

  • Natural selection drives adaptive evolution by selecting for and increasing the occurrence of beneficial traits in a population.
  • Natural selection only acts on the population's heritable traits: selecting for beneficial alleles and, thus, increasing their frequency in the population, while selecting against deleterious alleles and, thereby, decreasing their frequency.
  • Natural selection does not act on individual alleles, however, but on entire organisms.
  • As natural selection influences the allele frequencies in a population, individuals can either become more or less genetically similar and the phenotypes displayed can become more similar or more disparate.
  • Through natural selection, a population of finches evolved into three separate species by adapting to several difference selection pressures.

• Forced Vibrations and Resonance

  • The phenomenon of driving a system with a frequency equal to its natural frequency is called resonance.
  • The phenomenon of driving a system with a frequency equal to its natural frequency is called resonance.
  • It is interesting that the widths of the resonance curves shown in depend on damping: the less the damping, the narrower the resonance.
  • The more selective the radio is in discriminating between stations, the smaller its damping.
  • Resonance occurs when the driving frequency equals the natural frequency, and the greatest response is for the least amount of damping.

• Frequency of Sound Waves

  • The perception of frequency is called pitch.
  • The perception of frequency is called pitch.
  • Frequency is dependent on wavelength and the speed of sound.
  • Different species can hear different frequency ranges.
  • Three flashing lights, from lowest frequency (top) to highest frequency (bottom). f is the frequency in hertz (Hz); or the number of cycles per second.

• Guidelines for Plotting Frequency Distributions

  • In statistics, the frequency (or absolute frequency) of an event is the number of times the event occurred in an experiment or study.
  • These frequencies are often graphically represented in histograms.
  • The relative frequency (or empirical probability) of an event refers to the absolute frequency normalized by the total number of events.
  • The height of a rectangle is also equal to the frequency density of the interval, i.e., the frequency divided by the width of the interval.
  • Depending on the actual data distribution and the goals of the analysis, different bin widths may be appropriate, so experimentation is usually needed to determine an appropriate width.

• The Photoelectric Effect

  • The energy of the emitted electrons does not depend on the intensity of the incoming light (the number of photons), only on the energy or frequency of the individual photons.
  • This frequency is called the threshold frequency.
  • where h is the Planck constant (6.626 x 10-34 m2kg/s) and f is the frequency of the incident photon.
  • where f0 is the threshold frequency for the metal.
  • The photocathode contains combinations of materials, such as caesium, rubidium, and antimony, specially selected to provide a low work function, so when illuminated by even very low levels of light, the photocathode readily releases electrons.

• RLC Series Circuit: At Large and Small Frequencies; Phasor Diagram

  • Response of an RLC circuit depends on the driving frequency—at large enough frequencies, inductive (capacitive) term dominates.
  • Now, we will examine the system's response at limits of large and small frequencies.
  • At large enough frequencies $(\nu \gg \frac{1}{\sqrt{2\pi LC}})$, XL is much greater than XC.
  • The impedance Z at small frequencies $(\nu \ll \frac{1}{\sqrt{2\pi LC}})$ is dominated by the capacitive term, assuming that the frequency is high enough so that XC is much larger than R.
  • Distinguish behavior of RLC series circuits as large and small frequencies

• Structure of the Chi-Squared Test

  • The chi-square test is used to determine if a distribution of observed frequencies differs from the theoretical expected frequencies.
  • The chi-square ($\chi^2$) test is a nonparametric statistical technique used to determine if a distribution of observed frequencies differs from the theoretical expected frequencies.
  • Thus, instead of using means and variances, this test uses frequencies.
  • Simple random sample – The sample data is a random sampling from a fixed distribution or population where each member of the population has an equal probability of selection.
  • The chi-square distribution takes slightly different shapes depending on how many categories (degrees of freedom) our variables have.

• Resonance in RLC Circuits

  • Frequencies at which the response amplitude is a relative maximum are known as the system's resonance frequencies.
  • The reactances vary with frequency $\nu$, with XL large at high frequencies and XC large at low frequencies given as:
  • $\nu_0$ is the resonant frequency of an RLC series circuit.
  • A variable capacitor is often used to adjust the resonance frequency to receive a desired frequency and to reject others. is a graph of current as a function of frequency, illustrating a resonant peak in Irms at $\nu_0 = f_0$.
  • Thus higher-resistance circuits do not resonate as strongly, nor would they be as selective in, for example, a radio receiver.

• Hardy-Weinberg Principle of Equilibrium

  • We can also write this as p + q = 1.If the frequency of the Y allele in the population is 0.6, then we know that the frequency of the y allele is 0.4.
  • From the Hardy-Weinberg principle and the known allele frequencies, we can also infer the frequencies of the genotypes.
  • The frequency of homozygous pp individuals is p2; the frequency of hereozygous pq individuals is 2pq; and the frequency of homozygous qq individuals is q2.
  • The frequency of heterozygous plants (2pq) is 2(0.6)(0.4) = 0.48.
  • The genetic variation of natural populations is constantly changing from genetic drift, mutation, migration, and natural and sexual selection.