Question 1

An ideal procedure for fetal testing in humans would have which of the following features?

Accepted Answer

The answer of An ideal procedure for fetal testing in...

Question 2

Hutchinson-Gilford progeria is an exceedingly rare human genetic disorder in which there is very early senility and death, usually from coronary artery disease, at an average age of approximately 13. Patients, who look very old even as children, do not live to reproduce. Which of the following represents the most likely assumption?

Accepted Answer

The fact that patients with Hutchinson-Gilford progeria die before reproductive age indicates that the disorder is likely caused by a mutation in a single gene that affects development and/or maintenance of a crucial system, such as the cardiovascular system. Therefore, it is most likely caused by a mutation in a single protein-coding gene.

Note: None of the other assumptions are necessarily true based on the given information.

Question 3

Use Figure 14.1 and the following description to answer the questions below.
In a particular plant, leaf color is controlled by gene locus D. Plants with at least one allele D have dark green leaves, and plants with the homozygous recessive dd genotype have light green leaves. A true-breeding dark-leaved plant is crossed with a light-leaved one, and the F₁ offspring is allowed to self-pollinate. The predicted outcome of the F₂ is diagrammed in the Punnett square shown in Figure 14.1, where 1, 2, 3, and 4 represent the genotypes corresponding to each box within the square.
  
Figure 14.1
-Which of the boxes correspond to plants with a heterozygous genotype?

Accepted Answer

Box 2 and Box 3 correspond to plants with a heterozygous genotype, typically represented as having two different alleles (e.g., Aa).

Question 4

Use Figure 14.1 and the following description to answer the questions below.
In a particular plant, leaf color is controlled by gene locus D. Plants with at least one allele D have dark green leaves, and plants with the homozygous recessive dd genotype have light green leaves. A true-breeding dark-leaved plant is crossed with a light-leaved one, and the F₁ offspring is allowed to self-pollinate. The predicted outcome of the F₂ is diagrammed in the Punnett square shown in Figure 14.1, where 1, 2, 3, and 4 represent the genotypes corresponding to each box within the square.
  
Figure 14.1
-Which of the boxes marked 1-4 correspond to plants with dark leaves?

Accepted Answer

Plants with dark leaves typically have a high concentration of chlorophyll, which is necessary for photosynthesis. This characteristic allows them to absorb a wide spectrum of light, making them efficient in various light conditions. Without specific details about the plants in the boxes, one can infer that options including multiple boxes might suggest a range of plants adapted to different environments, hence the selection of an option that includes multiple boxes. However, without specific information about the characteristics of the plants in each box, this question cannot be accurately answered. My response is based on a general understanding of plant biology and the common characteristic of dark leaves being associated with high chlorophyll content.

Question 5

Which of the following provides an example of epistasis?

Accepted Answer

Epistasis occurs when one gene masks or modifies the expression of another gene. In this case, the presence of the cc genotype prevents the expression of any fur color genes, regardless of what other genes may be present.

Question 6

Hydrangea plants of the same genotype are planted in a large flower garden. Some of the plants produce blue flowers and others pink flowers. This can be best explained by which of the following?

Accepted Answer

The color of hydrangea flowers is determined by the concentration of metal ions in the soil, particularly aluminum ions. In acidic soil, aluminum ions are more available, resulting in blue flowers. In alkaline soil, aluminum ions are less available, resulting in pink flowers. Therefore, the color difference is due to environmental factors like soil pH, and not genetics.

Question 7

The following questions refer to the pedigree chart in Figure 14.2 for a family, some of whose members exhibit the dominant trait, W. Affected individuals are indicated by a dark square or circle.
  
Figure 14.2
-What is the genotype of individual II-5?

Accepted Answer

The genotype of individual II-5 is "ww" because it is typically determined by the inheritance pattern shown in a pedigree chart, where "ww" would indicate a recessive trait being expressed.

Question 8

Phenylketonuria (PKU)is a recessive human disorder in which an individual cannot appropriately metabolize a particular amino acid. The amino acid is not otherwise produced by humans. Therefore, the most efficient and effective treatment is which of the following?

Accepted Answer

The most effective treatment for PKU is to regulate the diet of the affected persons to severely limit the uptake of the amino acid. This can help prevent the buildup of toxic byproducts that can lead to serious neurological damage.

Question 9

Which of the following is an example of polygenic inheritance?

Accepted Answer

Skin pigmentation in humans is an example of a trait that is controlled by multiple genes, making it polygenic. Skin color is determined by the interaction of at least three genes, which is why there is a wide range of skin tones across human populations. ABO blood group is an example of multiple alleles, but not polygenic inheritance. Pink flowers in snapdragons and white and purple flower color in peas are both examples of incomplete dominance. Huntington's disease is caused by a single dominant allele.

Question 10

Most genes have many more than two alleles. However, which of the following is also true?

Accepted Answer

Even though genes may have many alleles, only two alleles can be present in an organism's genotype, one from each parent. Therefore, there may still be only two phenotypes for a trait, even if there are many alleles for that gene.

Question 11

Which of the following calculations require that you utilize the addition rule?

Accepted Answer

The addition rule is used when calculating the probability of mutually exclusive events, meaning that only one outcome can occur. In this case, the probability of a child having sickle-cell anemia and the probability of a child having cystic fibrosis are mutually exclusive. Therefore, we need to use the addition rule to calculate the probability of either outcome occurring.

Question 12

Which of the following describes the ability of a single gene to have multiple phenotypic effects?

Accepted Answer

Pleiotropy is the ability of a single gene to affect multiple phenotypic traits. For example, sickle cell anemia is caused by a single gene, but it affects multiple traits such as red blood cell shape, blood flow, and resistance to malaria. Incomplete dominance refers to a situation where a heterozygous phenotype is intermediate between the two homozygous phenotypes. Multiple alleles refer to the presence of more than two forms of a gene in a population. Epistasis refers to the interaction between two different genes, where one gene masks the expression of another gene.

Question 13

Cystic fibrosis affects the lungs, the pancreas, the digestive system, and other organs, resulting in symptoms ranging from breathing difficulties to recurrent infections. Which of the following terms best describes this?

Accepted Answer

Pleiotropy describes a situation where a single gene can affect multiple traits or organs. Cystic fibrosis is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, which affects various organs such as the lungs, pancreas, and digestive system.

Question 14

Use Figure 14.1 and the following description to answer the questions below.
In a particular plant, leaf color is controlled by gene locus D. Plants with at least one allele D have dark green leaves, and plants with the homozygous recessive dd genotype have light green leaves. A true-breeding dark-leaved plant is crossed with a light-leaved one, and the F₁ offspring is allowed to self-pollinate. The predicted outcome of the F₂ is diagrammed in the Punnett square shown in Figure 14.1, where 1, 2, 3, and 4 represent the genotypes corresponding to each box within the square.
  
Figure 14.1
-Which of the plants will be true-breeding?

Accepted Answer

True-breeding plants are those that, when self-fertilized, only produce offspring with the same traits. Choices 1 and 4 must represent plants that are homozygous for the traits in question, ensuring that they will consistently produce offspring with those same traits when self-fertilized.

Question 15

An obstetrician knows that one of her patients is a pregnant woman whose fetus is at risk for a serious disorder that is detectable biochemically in fetal cells. The obstetrician would most reasonably offer which of the following procedures to her patient?

Accepted Answer

The answer of An obstetrician knows that one of her...

Question 16

In cattle, roan coat color (mixed red and white hairs)occurs in the heterozygous (Rr)offspring of red (RR)and white (rr)homozygotes. Which of the following crosses would produce offspring in the ratio of 1 red:2 roan:1 white?

Accepted Answer

According to the question, roan coat color occurs in the heterozygous offspring of red and white homozygotes. Therefore, the roan coat color can only occur in the offspring of the roan (Rr) and not in the offspring of pure red (RR) or pure white (rr) individuals. 
When two roan individuals are crossed (Rr × Rr), they can produce the following genotypic ratios: 
1 RR:2 Rr:1 rr 
This genotypic ratio can be translated to a phenotypic ratio of: 
1 red:2 roan:1 white 
Therefore, the best choice is B (roan × roan) to produce the desired phenotypic ratio.

Question 17

A scientist discovers a DNA-based test for one allele of a particular gene. This and only this allele, if homozygous, produces an effect that results in death at or about the time of birth. Of the following, which is the best use of this discovery?

Accepted Answer

Designing a test for identifying heterozygous carriers of the allele is the best use of this discovery because it allows for the identification of individuals who carry one copy of the allele (are heterozygous) and therefore have a risk of passing the allele to their offspring. This information can be crucial for genetic counseling and making informed reproductive choices, especially since the homozygous condition is lethal.

Question 18

The frequency of heterozygosity for the sickle-cell anemia allele is unusually high, presumably because this reduces the frequency of malaria. Such a relationship is related to which of the following?

Accepted Answer

The relationship described is an example of natural selection, as individuals who are heterozygous for the sickle-cell anemia allele have an advantage in regions with high malaria prevalence. This allows them to survive and reproduce at a higher rate than individuals with only one normal allele or two sickle-cell alleles, increasing the frequency of the sickle-cell allele in the population despite its harmful effects in homozygotes. This is an example of Darwin's theory of natural selection.

Question 19

How could you best predict the maximum number of alleles for a single gene whose polypeptide product is known?

Accepted Answer

The maximum number of alleles for a single gene is theoretically determined by the number of nucleotide positions in the gene that can vary. Since each position in the DNA sequence that codes for the polypeptide can potentially mutate to four different nucleotides (A, T, C, G), counting the number of DNA nucleotides in the code for the polypeptides gives the best prediction of the maximum number of alleles.

Question 20

One of two major forms of a human condition called neurofibromatosis (NF 1)is inherited as a dominant gene, although it may range from mildly to very severely expressed. If a young child is the first in her family to be diagnosed, which of the following is the best explanation?

Accepted Answer

Since the condition is inherited as a dominant gene, it means that if a parent has it, there is a 50% chance of passing it on to their child. Therefore, one of the parents must have the gene, but with very mild expression, making it difficult to diagnose until their child is born with a more severe expression of the gene.

Quiz 14: Mendel and the Gene Idea