Several features of Gregor Mendel's experiments on plant breeding and patterns of inheritance distinguished his work from that of his contemporaries. Which of the following was a critical experimental innovation employed by Mendel that distinguished his experiments from those of his contemporaries?A. Mendel used self-fertilizing wild strains in his experiments. B. Mendel restricted his observations to the first-generation progeny from his crosses. C. Mendel performed controlled crosses with pure-breeding strains. D. Mendel used strains that displayed a broad range of phenotypes for each trait.

The correct answer is: C.

Explanation:

Gregor Mendel identified the manner in which different traits are transferred from the parents to their offspring.He explained the three Laws which determines the pattern of inheritance by examining the some traits of pea plant in the parental and offspring generation.The traits includes, seed colour seed shape, pod colour, etc.The parent pea plants which Mendel experimented with belonged to the pure-breeding strains.This means that the parent pea plants were homozygous (either dominant or recessive) and not heterozygous for the different traits which Mendel observed.This is why Mendel could determine the pattern of inheritance of the traits in different generations of the offspring.The three laws of inheritance as explained by Mendel were,The Law of Dominance. It states that in a diploid organism, each trait is controlled by two contrasting variants of the same gene called Alleles. Among the two variants one can express itself even in the presence of the other variant (heterozygous condition) and is called the Dominant allele. The other variant gets suppressed in the presence of the dominant allele and can express itself only in the homozygous condition. This is the Recessive allele.The Law of Segregation. It states that different pair of alleles segregate during the formation of gametes and during the process of fertilization they associate with the corresponding allele, obtained from the other parent, randomly.The Law of Independent Assortment. It states that during gamete formation, alleles of two different genes get randomly sorted in the gametes independent of each other.

Mantle convection  is the slow  creepingmotion of earth's solid silicate  mantle  caused by  convection  currents carrying  heat from the interior  to the planet's surface.[1][2]  the earth's surface  lithosphere, which rides atop the  asthenosphere  (the two components of the  upper mantle), is divided into a number of  plates  that are continuously being created and consumed at their opposite  plate boundaries. accretion occurs as mantle is added to the growing edges of a plate, associated with  seafloor spreading. this hot added material cools down by  conduction  and  convection  of heat. at the consumption edges of the plate, the material has thermally contracted to become dense, and it sinks under its own weight in the process of  subduction  usually at an  ocean trench.[3]this subducted material sinks through the earth's interior. some subducted material appears to reach the lower mantle,[4]  while in other regions, this material is impeded from sinking further, possibly due to a phase transition from  spinel  to  silicate perovskiteand  magnesiowustite, an  endothermic reaction.[5]the subducted oceanic crust triggers  volcanism, although the basic mechanisms are varied. volcanism may occur due to processes that add buoyancy to partially melted mantle causing an upward flow due to a decrease in density of the partial melt.secondary forms of convection that may result in surface volcanism are postulated to occur as a consequence of intraplate extension[6]  and  mantle plumes.[7]it is because the mantle can convect that the  tectonic plates  are able to move around the earth's surface.[8]mantle convection seems to have been much more active during the  hadean  period, resulting in gravitational sorting of heavier molten  iron, and  nickel  elements and  sulphides  in the core, and lighter  silicate minerals  in the  mantle.