(Choices B, C, and F) Catecholamines (eg, epinephrine, norepinephrine) and glucagon attenuate hypoglycemia. However, they exert their metabolic effects via extraceffular, transmembrane, G protein-coupled receptors that activate adenyl cyclase and increase cyclic AMP production.
(Choice D) Growth hormone acts via an extracellular, transmembrane receptor that activates a JAK-STAT pathway. Growth hormone antagonizes insulin action, increases gluconeogenesis, and promotes lipolysis (provides gluconeogenic substrates).
(Choice E) In addition to the production of counterregulatory hormones, the inhibition of insulin release from pancreatic beta cells plays a primary role in preventing hypoglycemia during fasting. However, insulin acts on an extrace/lu/artransmembrane receptor with intrinsic tyrosine kinase activity.

(Choice A) DNA ligase is the enzyme that repairs single-strand breaks in duplex DNA during DNA replication and repair.
(Choices B and C) During replication, DNA polymerase Ill is the primary enzyme responsible for synthesis of daughter DNA strands; DNA polymerase I functions chiefly to replace the RNA primers with DNA segments. Unlike DNA polymerase Ill, DNA polymerase I has 5’→3′ exonuclease activity that can remove RNA primers and damaged DNA segments. The 3’→ 5′ exonuclease activity of DNA polymerase I and Ill provides a proofreading function that fixes mismatched nucleotides in the newly formed daughter strands.
(Choices D and E) Helicase unwinds DNA at the replication fork. However, this process results in supercoiling of the DNA. DNA gyrase is a type II topoisomerase that helps to relieve the resultant strain.

(Choice A) Dominant negative mutations occur when an abnormal gene negatively affects the product of the wildtype gene in the same cell. For example, certain oncogene p53 mutations can lead to translation of a protein product that prevents wild-type p53 from binding to the promoter of its target genes.
(Choice B) Genetic linkage describes the tendency of alleles located near one another on the same chromosome to be inherited jointly.
(Choice C) Penetrance refers to the proportion of individuals with a given genotype that express the associated phenotype. In incomplete penetrance, less than 100% of individuals with a given genotype express its associated phenotype.
(Choice D) Locus heterogeneity refers to the ability of one disease or trait to be caused by mutations in multiple different genes. An example is familial hypercholesteremia, which can be caused by different mutations affecting cholesterol metabolism genes (eg, LDL receptor, apo B-100).
(Choice F) Polyploidy occurs when more than 2 complete sets of homologous chromosomes exist within an organism or cell . In a partial hydatidiform mole, for example, there are cells of nonstandard ploidy (typically 69,XXX; 69,XXY; or 69,XYY). The chromosomes in this case are derived from 1 haploid maternal set and 2 haploid paternal sets of chromosomes.
(Choice G) The law of segregation (Mendel’s first law) describes the phenomenon whereby gametogenesis within the parent organism results in the separation of paired alleles so that each offspring inherits only half of each parent’s genetic composition.