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Example Questions
Example Question #1061 : Mcat Biological Sciences
The Urey-Miller experiment determined which of the following results?
Cyanobacteria were responsible for the oxygenation of the atmosphere
DNA replicates via semiconservative replication
Organic molecules can arise from inorganic precursors
The early atmosphere was composed of ammonia and methane
Organic molecules can arise from inorganic precursors
The Urey-Miller experiment was used to determine if the early atmospheric conditions were favorable for the creation of organic materials. Their experiments determined that basic organic molecules, such as urea and amino acids, were able to form in early atmospheric conditions.
The Mehselson-Stahl experiment revealed the semi-conservative nature of DNA replication.
Example Question #1062 : Mcat Biological Sciences
Seven thousand years ago, a species of oryx indigenous to the Arabian Peninsula was separated when an earthquake caused an insurmountable barrier to form between different geological segments of the population. A recent population genetics study showed that the two populations were no longer able to successfully interbreed.
Careful testing of these two species found that a physiological change in one species was responsible for the mating incompatibility between the two populations. Which of the following answer choices best describes the nature of this mating incompatibility?
Temporal difference
Mechanical difference
Genetic difference
Inherent difference
Mechanical difference
A physiological condition making two speciated animals unable to mate is a mechanical difference.
Example Question #1063 : Mcat Biological Sciences
A population of saltwater fish has doubled in body length and decreased in body width over the past decade. This has been attributed to overfishing using nets with large holes. This type of selection is most accurately __________.
disruptional selection
stabilizing selection
directional selection
unnatural selection
phenotypical selection
directional selection
Directional selection is when a population undergoes a change biased in a certain direction away from the original average of the population. Since the fish are getting bigger in once sense and smaller in another, this is directional selection.
Example Question #1064 : Mcat Biological Sciences
Seven thousand years ago, a species of oryx indigenous to the Arabian Peninsula was separated when an earthquake caused an insurmountable barrier to form between different geological segments of the population. A recent population genetics study showed that the two populations were no longer able to successfully interbreed.
What type of speciation event does this information indicate?
None of these
Parapatric speciation
Peripatric speciation
Allopatric speciation
Artificial speciation
Allopatric speciation
Allopatric speciation occurs when a physical barrier, or in some cases emigration of subpopulations of a species, prevents interspecies mingling that eventually leads to the inability to interbreed. Sympatric speciation describes a process by which new species form while in the same geographic location. Parapatric and peripatric speciation are subcategories of sympatric speciation.
Example Question #1062 : Mcat Biological Sciences
Passage:
A population of 1200 flamingos exists on an island in the tropics. The flamingos had previously been studied for many years due to their fascinating foraging habits. Many flamingos within this population hunt their prey out in the open, without any attempts to disguise themselves, which some feel predisposes them to being seen by their prey and evaded, or even attacked, sooner than flamingos who more stealthily hunt their prey. Still, so many of these flamingos continue to live viably and reproduce highly successfully, so it has puzzled scientists for years that this is an "evolutionarily successful" strategy. Of the 1200 flamingos initially present, 800 had pink feathers and 400 had white feathers. A tragic hurricane then struck the island, killing all but 10 of the flamingos. 8 of these 10 had white feathers. Years later, scientists again studied the flamings on the island and found a population of 600 flamingos. Of the 600 flamingos, 560 had white feathers and 40 had pink feathers.
Which of the following evolutionary principles best describes the situation present in the passage above?
Genetic Drift
Bottlenecking
Spontaneous Mutation
Selective Mating
Genetic Engineering
Bottlenecking
The situation described is a classic example of the evolutionary principle of "bottlenecking," making this the best answer choice. Bottlenecking describes the phenomenon in which the genetic diversity of a population changes suddenly, often due to a natural disaster, which then results in future generations appearing more genetically and phenotypically similar to one another than in the pre-disaster generations. In this instance, pink flmaginos were initially more common than white flamingos, but both were fairly prevalent. They then encounter a hurricane that kills all but a few flamingos, which were almost entirely white-feathered, which led to all ensuing generations being predominantly white-feathered.
This does not represent "selective mating," "spontaneous mutation," or "genetic engineering," as white-feathered flamingos became most prevalent due to a natural disaster, not white flamingos selectively seeking to mate with other white flamingos, not due to a single mutation, and not due to scientists artificially manipulating the genes within the flamingos.
This does not represent "genetic drift," because the changes in phentype prevalence were not due to random chance fluctuations, they were due to an explainable event, a natural disaster that resulted in an initially low number of white flamingos remaining and becoming most predominant.
Example Question #1065 : Mcat Biological Sciences
Inbreeding reduces the fitness of a population. This is the result of which increased genetic effect of inbreeding?
Levels of aggression
Rate of spontaneous mutation
Genetic diversity
Expression of deleterious recessive traits
Expression of deleterious recessive traits
Inbreeding increases the expression of recessive traits due to more heterozygous carriers mating with each other. As the same individuals mate, the chance of a homozygous recessive child increases. This is the same as estimating the likelihood of a single healthy child from two carrier parents (0.75) versus eight healthy children from two carrier parents (0.10).
Inbreeding decreases genetic diversity, rather than increasing it. The rate of spontaneous mutation is not impacted by this type of breeding. There is no reason to infer increased levels of aggression.
Example Question #15 : Evolution
Which is not a necessary condition for the Hardy-Weinberg equation to be true?
No natural selection
No net migration of individuals into or out of the population
No mutations in the gene pool
Small population
Random mating
Small population
For the Hardy-Weinberg equation to be true, the population in question must be very large. This ensures that coincidental occurrences do not drastically alter allelic frequencies.
Example Question #1 : Evolutionary Factors
In a population that is in Hardy-Weinberg equilibrium, the frequency of homozygous dominant individuals is 0.36. What is the percentage of homozygous recessive individuals in the population?
The two equations pertaining to Hardy-Weinberg equilibrium are:
In this second equation, each term refers to the frequency of a given genotype. is the homozygous dominant frequency, is the heterozygous frequency, and is the homozygous recessive frequency.
From the question, we know that:
We now know the dominant allele frequency. Using the other Hardy-Weinberg equation, we can find the recessive allele frequency:
Returning to our genotype frequency terms, we can use this recessive allele frequency to find the homozygous recessive frequency:
Example Question #1 : Genetics
A diploid human cell that is dividing will contain _______ chromosomes. These chromosomes will each consist of _______ chromatids. Fill in the corresponding blanks.
46, 1
92, 2
23, 1
46, 2
23, 2
46, 2
The diploid number is 46 and the haploid number is 23. When cells are dividing, each chromosome is present in duplicate copy. These chromosomes are composed of two chromatids each when they are replicated.
Example Question #2 : Genetics
Human chromosomes are divided into two arms, a long q arm and a short p arm. A karyotype is the organization of a human cell’s total genetic complement. A typical karyotype is generated by ordering chromosome 1 to chromosome 23 in order of decreasing size.
When viewing a karyotype, it can often become apparent that changes in chromosome number, arrangement, or structure are present. Among the most common genetic changes are Robertsonian translocations, involving transposition of chromosomal material between long arms of certain chromosomes to form one derivative chromosome. Chromosomes 14 and 21, for example, often undergo a Robertsonian translocation, as below.
A karyotype of this individual for chromosomes 14 and 21 would thus appear as follows:
Though an individual with aberrations such as a Robertsonian translocation may be phenotypically normal, they can generate gametes through meiosis that have atypical organizations of chromosomes, resulting in recurrent fetal abnormalities or miscarriages.
In a normal chromosome 14, what region of the chromosome exists between the p arm and the q arm?
Centromere
Single nucleotide polymorphism
Intron
Telomere
Exon
Centromere
In a normal chromosome, the passage indicates that the p and q arm meet in the center. This central region of the chromosome is known as a centromere.
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