Scientists have examined the genetic history of a large group of cheetahs and have found that
there was a significant decrease in the genetic diversity of the cheetah species about 10,000 years
ago. Scientists found that, even in unrelated groups of cheetahs, individual cheetahs had 99% of
the same alleles. By comparison, in a genetically diverse population, even closely related
individuals contain only 80% of the same alleles. Genetic diversity is important to the survival of a
species, and scientists worry that a disease that cheetahs are not resistant to could decimate the
population.
Major histocompatibility complex (MC) genes are used by the body to identify self from non-self
and direct the immune system to attack non-self particles. Invading bacteria and viruses do not
contain the same MHC genes and therefore are attacked by the immune system. Within a
population, a high diversity of MHC genes protects the population from attack by disease. In a
highly diverse population, it is likely that at least some individuals will contain an allele that
identifies a new disease as non-self and can direct the immune system to destroy it.
In 1985, research by Stephen O'Brien reported that skin grafts from cheetahs in a zoo in Oregon
were accepted by cheetahs in Africa. Skin grafts, like other organ donations, must be between
Individuals that have the same MHC factors. If any of the genetic factors are different, then the
immune system of the individual receiving the organ will identify the organ as non-self and the
body will attack the donated organ as if it were a foreign organism such as a virus or bacterium.
The conclusion from
O'Brien's research was that cheetah MHC genes are as alike as those of identical twins.
More recent research by Simone Sommer took a much more comprehensive approach to
examining the genes of a large sample of wild cheetahs. Sommer's research determined how
many alleles are present on two different types of MHC genes in approximately 150 cheetahs.
Sommer was able to show that the variation in some MHC genes was higher than previously
thought. The variation in MHC genes in cheetahs is still smaller than that for other big cat species
but appears to be sufficient to allow the populations to identify a wide variety of foreign particles.
Sommer's research concludes that cheetahs have sufficient genetic diversity to respond to common diseases, but may still be at risk of new diseases. Which statement from the passage supports this conclusion?
- A. Major histocompatibility complex (MHC) genes are used by the body to identify self from non-self...
- B. The variation in MHC genes in cheetahs is still smaller than that for other big cat species but appears to be sufficient...
- C. If any of the genetic factors are different, then the immune system of the individual...
- D. Sommer's research determined how many alleles are present on two different types of MHC genes...
Correct Answer & Rationale
Correct Answer: B
Option B directly supports Sommer's conclusion by highlighting that the variation in MHC genes among cheetahs, while less than in other big cats, is adequate for their immune response to common diseases. This indicates sufficient genetic diversity for disease management, aligning with the research's findings. Option A discusses the function of MHC genes but does not address their variation in cheetahs, making it less relevant. Option C mentions genetic factors affecting immune response but lacks specific information about cheetah genetic diversity. Option D focuses on the number of alleles without linking it to the implications for disease response, thus failing to support the conclusion effectively.
Option B directly supports Sommer's conclusion by highlighting that the variation in MHC genes among cheetahs, while less than in other big cats, is adequate for their immune response to common diseases. This indicates sufficient genetic diversity for disease management, aligning with the research's findings. Option A discusses the function of MHC genes but does not address their variation in cheetahs, making it less relevant. Option C mentions genetic factors affecting immune response but lacks specific information about cheetah genetic diversity. Option D focuses on the number of alleles without linking it to the implications for disease response, thus failing to support the conclusion effectively.
Other Related Questions
Based on these results and assuming that whenever two materials are present their remaining energy is averaged, what would the scientist best conclude to be the composition of Saturn's rings?
- A. equal amounts of loose rocks and loose snow
- B. equal amounts of ice and bedrock
- C. a small amount of bedrock and a large amount of carbon rock
- D. large amounts of ice and smaller amounts of carbon rock
Correct Answer & Rationale
Correct Answer: D
The conclusion about Saturn's rings is supported by the composition of ice and carbon rock. Large amounts of ice are consistent with observations of Saturn’s rings, which are primarily composed of water ice particles. Smaller amounts of carbon rock align with the presence of darker materials found in the rings. Options A and B suggest equal amounts of materials that do not reflect the observed predominance of ice. Option C overestimates the presence of bedrock, which is not supported by scientific data. Thus, option D accurately captures the dominant composition of Saturn's rings.
The conclusion about Saturn's rings is supported by the composition of ice and carbon rock. Large amounts of ice are consistent with observations of Saturn’s rings, which are primarily composed of water ice particles. Smaller amounts of carbon rock align with the presence of darker materials found in the rings. Options A and B suggest equal amounts of materials that do not reflect the observed predominance of ice. Option C overestimates the presence of bedrock, which is not supported by scientific data. Thus, option D accurately captures the dominant composition of Saturn's rings.
Two people are standing at the edge of a high cliff. One person throws a rock horizontally off the cliff. Which uncontrolled part of this investigation can prevent the rocks from hitting the ground at the same time?
- A. gravity
- B. mass of the rocks
- C. air resistance
- D. strength of the person
Correct Answer & Rationale
Correct Answer: C
When a rock is thrown horizontally, it is influenced by both gravity and air resistance. Gravity acts equally on both rocks, ensuring they fall at the same rate. The mass of the rocks does not affect the time it takes to hit the ground in a vacuum, as all objects fall at the same rate regardless of mass. The strength of the person throwing the rock only affects the initial horizontal velocity, not the fall time. However, air resistance can vary based on the shape and size of the rocks, potentially causing differences in descent time. Thus, air resistance is the uncontrolled factor that can prevent the rocks from hitting the ground simultaneously.
When a rock is thrown horizontally, it is influenced by both gravity and air resistance. Gravity acts equally on both rocks, ensuring they fall at the same rate. The mass of the rocks does not affect the time it takes to hit the ground in a vacuum, as all objects fall at the same rate regardless of mass. The strength of the person throwing the rock only affects the initial horizontal velocity, not the fall time. However, air resistance can vary based on the shape and size of the rocks, potentially causing differences in descent time. Thus, air resistance is the uncontrolled factor that can prevent the rocks from hitting the ground simultaneously.
A diagram of a PV cell being exposed to sunlight is shown below. Click on the labels you want to select and drag them into the boxes to show the components of the PV cell.
- A. Phosphorus-injected layer
- B. Boron-injected layer
- C. Electric field
- D. Energy
Correct Answer & Rationale
Correct Answer: A,B,C
The components of a photovoltaic (PV) cell include the phosphorus-injected layer, which serves as the n-type semiconductor, and the boron-injected layer, acting as the p-type semiconductor. Together, these layers create a junction that facilitates the movement of electrons when exposed to sunlight. The electric field between these layers is crucial for separating charge carriers, enabling electricity generation. Option D, "Energy," is not a structural component of the PV cell but rather a result of its operation. It does not represent a physical part of the cell, making it an incorrect choice.
The components of a photovoltaic (PV) cell include the phosphorus-injected layer, which serves as the n-type semiconductor, and the boron-injected layer, acting as the p-type semiconductor. Together, these layers create a junction that facilitates the movement of electrons when exposed to sunlight. The electric field between these layers is crucial for separating charge carriers, enabling electricity generation. Option D, "Energy," is not a structural component of the PV cell but rather a result of its operation. It does not represent a physical part of the cell, making it an incorrect choice.
The equation for photosynthesis is often written as shown below. Based on this equation, what does the triangle symbol represent?
- A. oxygen
- B. chloroplast
- C. heat
- D. light
Correct Answer & Rationale
Correct Answer: D
In the equation for photosynthesis, the triangle symbol represents light, which is essential for the process to occur. Plants capture light energy to convert carbon dioxide and water into glucose and oxygen. Option A, oxygen, is a product of photosynthesis but not represented by the triangle. Option B, chloroplast, is the organelle where photosynthesis takes place, but it is not indicated by the triangle symbol. Option C, heat, is not a direct component of the photosynthesis equation, as it does not play a role in the conversion process. Thus, light is the critical factor denoted by the triangle.
In the equation for photosynthesis, the triangle symbol represents light, which is essential for the process to occur. Plants capture light energy to convert carbon dioxide and water into glucose and oxygen. Option A, oxygen, is a product of photosynthesis but not represented by the triangle. Option B, chloroplast, is the organelle where photosynthesis takes place, but it is not indicated by the triangle symbol. Option C, heat, is not a direct component of the photosynthesis equation, as it does not play a role in the conversion process. Thus, light is the critical factor denoted by the triangle.