assortative mating

Examples of assortative mating in the following topics:

• Nonrandom Mating and Environmental Variance

  • Population structure can be altered by nonrandom mating (the preference of certain individuals for mates) as well as the environment.
  • If individuals nonrandomly mate with other individuals in the population, i.e. they choose their mate, choices can drive evolution within a population.
  • There are many reasons nonrandom mating occurs.
  • One common form of mate choice, called positive assortative mating, is an individual's preference to mate with partners that are phenotypically similar to themselves.
  • The American Robin may practice assortative mating on plumage color, a melanin based trait, and mate with other robins who have the most similar shade of color.

• Mating Systems and Sexual Selection

  • In mating, there are two types of selection (intersexual, intrasexual) and three mating systems (monogamous, polygynous, polyandrous).
  • Intrasexual selection involves mating displays and aggressive mating rituals such as rams butting heads; the winner of these battles is the one that is able to mate.
  • Polygynous mating refers to one male mating with multiple females.
  • In polyandrous mating systems, one female mates with many males.
  • Seahorses are a good example of a polyandrous mating system, in which one female mates with several males.

• Life Cycles of Sexually Reproducing Organisms

  • During sexual reproduction, specialized haploid cells from two individuals, designated the (+) and (−) mating types, join to form a diploid zygote.
  • The mechanisms of variation (crossover, random assortment of homologous chromosomes, and random fertilization) are present in all versions of sexual reproduction.

• Epistasis

  • The recessive yellow genotype is epistatic to the B gene: mating two heterozygotes (BbEe) results in a 9:3:4 ratio of black (B_E_) to brown (bbE_) to yellow (__ee) offspring.
  • Note that we are assuming the interacting genes are not linked; they are still assorting independently into gametes.

• Mendel's Law of Independent Assortment

  • Independent assortment allows the calculation of genotypic and phenotypic ratios based on the probability of individual gene combinations.
  • Mendel's law of independent assortment states that genes do not influence each other with regard to the sorting of alleles into gametes: every possible combination of alleles for every gene is equally likely to occur.
  • The independent assortment of genes can be illustrated by the dihybrid cross: a cross between two true-breeding parents that express different traits for two characteristics.
  • The law of independent assortment states that a gamete into which an r allele sorted would be equally likely to contain either a Y allele or a y allele.
  • The values along each forked pathway can be multiplied because each gene assorts independently.

• Signaling in Yeast

  • Yeasts utilize cell-surface receptors, mating factors, and signaling cascades in order to communicate.
  • In order to find another haploid yeast cell that is prepared to mate, budding yeasts secrete a signaling molecule called mating factor.
  • When mating factor binds to cell-surface receptors in other yeast cells that are nearby, they stop their normal growth cycles and initiate a cell signaling cascade that includes protein kinases and GTP-binding proteins that are similar to G-proteins.
  • Budding Saccharomyces cerevisiae yeast cells can communicate by releasing a signaling molecule called mating factor.

• Sexual Selection

  • Sexual selection, the selection pressure on males and females to obtain matings, can result in traits designed to maximize sexual success.
  • The selection pressures on males and females to obtain matings is known as sexual selection.
  • Females almost always mate, while mating is not guaranteed for males.
  • The bigger, stronger, or more decorated males usually obtain the vast majority of the total matings, while other males receive none.
  • In either case, this variation in reproductive success generates a strong selection pressure among males to obtain those matings, resulting in the evolution of bigger body size and elaborate ornaments in order to increase their chances of mating.

• Animal Communication and Living in Groups

  • Mating usually involves one animal signaling another so as to communicate the desire to mate.
  • There are several types of energy-intensive behaviors or displays associated with mating called mating rituals.
  • Male crickets make chirping sounds using a specialized organ to attract a mate, repel other males, and to announce a successful mating.
  • If at any point the display is performed incorrectly or a proper response is not given, the mating ritual is abandoned and the mating attempt will be unsuccessful.
  • A male peacock's extravagant, eye-spotted tail is used in courtship displays to attract a mate.

• Genetic Linkage and Violation of the Law of Independent Assortment

  • Genes that are on the same chromosome, or "linked", do not assort independently, but can be separated by recombination.
  • Although all of Mendel's pea characteristics behaved according to the law of independent assortment, we now know that some allele combinations are not inherited independently of each other.
  • Mendel's seminal publication makes no mention of linkage, and many researchers have questioned whether he encountered linkage, but chose not to publish those crosses out of concern that they would invalidate his independent assortment postulate.

• Mendelian Crosses

  • Mendel's crosses involved mating two true-breeding organisms that had different traits to produce new generations of pea plants.
  • Mendel performed crosses, which involved mating two true-breeding individuals that have different traits .