In the meiotic cell cycle, meiosis I is the only phase that includes a DNA replication step, or else the process would not result in haploid cells. As in mitosis, prophase is the step within which replication occurs.

The Punnett square for the cross is shown below. Each offspring has a 50% chance of inheriting a heterozygous phenotype and an equal chance of inheriting a homozygous recessive genotype (which results in the cinnabar phenotype).

C Remember your LEAST/EXCEPT/NOT technique. You should be familiar with the rules for blood typing in humans, but if you aren't, this question gives you the basics. Because the alleles IA and IB are codominant, a man with blood type AB can only have the genotype IAIB. The woman with blood type A could have either IAIA or IAi as her genotype. Here are the Punnett squares:

An enzyme speeds up the rate of a reaction by lowering the activation energy, making the transition state less stable. It does not affect the energy of the products or the reactants.

Polygenic inheritance describes traits that are influenced by multiple genes. Epistasis is an interaction between two genes, both affecting a phenotype. In contrast, pleiotropy occurs when a single gene influ-ences multiple traits.

The insertion of two nucleotides will shift the reading frame of all the codons "downstream" of the mutation, resulting in a series of mis-sense codons and eventually a nonsense (stop) codon.

The first organisms were heterotrophic prokaryotes. The evolution of photosynthetic prokaryotes (cyanobacteria) led to an increase in Earth's atmospheric oxygen level. Eukaryotes and metazoa (animals) then evolved.

DNA replication is semiconservative. During the first round of replication, each original single strand pairs with a new complementary strand. The first-generation daughter cells each have DNA consisting of one original and one new strand. During replication, the single original strand will pair with a new strand. The other double strand will consist of nonoriginal DNA.

D Anyone who has produced offspring has demonstrated their fitness. Regardless of how healthy a child is, he has not yet produced offspring to prove his fitness. Use the LEAST/EXCEPT/NOT technique.

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A stop codon terminates amino acid translation. If this occurs before the true end of a protein-coding sequence, the protein up to that point will be formed normally but then be truncated as an incomplete protein.

B cells and immature T cells are produced in the marrow of the long bones, such as the femur or thigh bone.

The ATP synthase enzyme, present in membranes, uses the power of hydrogen ions moving down their concentration gradient to add a phosphate group to ADP, producing ATP.

The first stage of meiosis divides the diploid set of chromosomes into two haploid sets. Homologous chromosomes separate in anaphase I, and at the beginning (prophase) of stage 2, each cell contains a haploid set. However, the chromosomes are still replicated and still consist of joined sister chromatids. These separate in anaphase II.

The adrenal medulla is a gland that responds to stress and creates a lasting response on the sympathetic nervous system, which none of the other options have an effect on.

A disorder that is only found in males must be Y linked. An X-linked trait would occur in a small proportion of females.

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B The endocrine system is a body control system, but it is NOT rapid. The fastest hormone in the body is adrenaline, and even that takes a few seconds, compared to the nervous system's milliseconds. Most hormones operate in the minutes to hours range. The other choices regarding the endocrine system are all true. Remember your LEAST/EXCEPT/NOT technique!

D The guard cells are found near the openings in the leaf called stomates. Stomates allow gas exchange to occur (notably oxygen and carbon dioxide), and while they are open water leaves through transpiration. You should have immediately eliminated choices A and E, because they are not leaf structures.

Pith is a source of unspecialized ground tissue that adds structure to a stem at the very center.

A somatic cell is diploid. If the organism's diploid chromosome number is 56, then the haploid gamete will possess half of this number of chromosomes, which is 28.

Algae are photosynthetic organisms that thrive in conditions of abundant nutrients such as nitrogen. A eutrophic lake is one that contains an overabundance of nutrients.

DNA in the cell's nucleus is a template for mRNA, which carries the information to the ribosome for translation. The new translated protein is further modified at the ER and Golgi body, respectively.

In eukaryotic chromosomes, DNA is tightly coiled and wound around histone proteins to form chromosomes.

The evolution of cyanobacteria, the first oxygen-releasing photosynthetic organisms, led to the accumulation of oxygen in Earth's surface waters and atmosphere. The oxygen reacted with dissolved iron, creating the oxides found in rocks.

The branches leading to Syrphoidea and Hippoboscoidea diverged from a common ancestor farthest back in time, indicating that this speciation event occurred earliest.

B cells and immature T cells are produced in the marrow of the long bones, such as the femur or thigh bone.

A The light reactions of photosynthesis convert solar energy to usable energy in the form of ATP (choices C and E are eliminated) and NADPH (a reduced electron carrier). The ATP and NADPH (i.e., energy) produced during these reactions are used later during the Calvin cycle to fix carbon dioxide into carbohydrates, like glucose. Because glucose is a product of the light-independent reactions, choice B could be eliminated. Remember that NADPH belongs with photosynthesis to eliminate choice D.

The induced-fit model states that the shape of the enzyme is altered by binding with the substrate. This is not a feature of the lock-and-key model. Neither model posits that the enzyme is changed by the reaction.

The fact that solute molecules are entering a cell via a membrane protein does not necessarily mean that the cell is expending energy (active transport), that the solute is moving against its concentration gradient (which requires energy), or that the solute concentration is greater inside the cell than outside (implying that the solute is moving against its concentration gradient). If the cell were in a hypotonic solution, solutes would tend to move out of the cell while water moved into it. Facilitated diffusion uses membrane protein to allow polar, hydrophilic molecules or ions into the cell. These solutes cannot pass through the nonpolar, hydrophobic inner layer of the cell membrane.

B Note that the plasmid has EcoRI sites, a HindIII site, and a PstI site. Because only EcoRI and HindIII are used, only those sites will be cut; the PstI site will effectively be ignored. To "digest to completion" means that the plasmid will be cut completely at those restriction sites. Three fragments will be produced, each corresponding to the distance (in kb) between the EcoRI and HindIII sites.

In order for there to be interspecific competition, each organism must occupy the same niche to some degree. Of all the listed examples, a deer and a hare are most likely to share food resources and habitat space, which would create competition between them.

Carbon dioxide is converted to a three-carbon sugar as part of the Calvin cycle, or dark reactions, which take place in the fluid stroma of the chloroplast. The remaining answer choices take place in the light reactions of photosynthesis, which take place in the thylakoids of the chloroplast.

The centromeres joining sister chromatids split in anaphase. The chromosomes are then pulled to opposite poles.

The anterior pituitary, located beneath the brain, secretes growth hormone.

Fungi, plants, and animals are all multicellular and possess nuclei within their cells, so this cannot be the answer. Many protists are unicellular, but they are still eukaryotic. Only Archaea and Eubacteria contain unicellular prokaryotic organisms.

Parathyroid hormone (PTH) is secreted in response to low blood calcium levels. This hormone acts on the kidneys to take up more calcium and causes bones to release calcium into the blood.

A Divergent evolution occurs when the same ancestral organism is placed into different environments and must then adapt to function in these different environments. Thus the same original structures evolve separately and "diverge" from one another. Examples of homologous structures are the arm of a man, the wing of a bat, and the flipper of a whale. All have the same basic bone structure but vastly different functions. The opposite of divergent evolution is convergent evolution, in which vastly different organisms are placed into the same environment and must adapt to perform similar functions with different structures. Convergent evolution produces analogous structures, examples of which are the wings of bats, the wings of birds, and the wings of butterflies. Speciation is often the result of divergent evolution, not the cause of it.

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A type III survivorship curve indicates an organism that produces many offspring, many of which do not survive over time. A type II curve represents organisms that produce several offspring, a decent proportion of which survive over time. A type I curve represents an organism that produces very few offspring, most of which survive over time.