Polygenic inheritance occurs when a single phenotypic trait is controlled by two or more different genes at different loci, each having an additive effect. Human skin color, height, and eye color are controlled by multiple genes (e.g., at least three genes for skin color). This results in a continuous range of phenotypes, forming a bell-shaped curve in a population.
Explanation:
Messenger RNA (mRNA) is transcribed from DNA in the nucleus and carries the codon sequence to ribosomes in the cytoplasm for translation into protein. tRNA brings amino acids, rRNA forms ribosomes, DNA stays in the nucleus. mRNA is the template for protein synthesis.
Explanation:
Phloem is composed of sieve tube elements, companion cells, phloem parenchyma, and phloem fibers. Sieve tubes are living cells that transport organic solutes; companion cells assist in loading and unloading. Tracheids and vessels are xylem elements. Fibers and sclereids are sclerenchyma cells. Guard cells regulate stomatal movement.
Explanation:
Lenticels are small, raised pores in the bark (periderm) of woody stems and roots that permit gas exchange between internal tissues and the atmosphere. Stomata are on leaves, hydathodes are for guttation, sclereids are sclerenchyma cells. Lenticels are filled with loosely arranged complementary cells and are visible as small dots on the surface of bark.
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