Passage
Lipopolysaccharides (LPS) found in gram-negative bacterial cells can elicit a lethal degree of adjuvanticity, or immune activation, in LPS-responsive host organisms. In mice, responses may be modulated by abnormalities in the toll-like receptor (TLR) encoded by the Tlr4 gene closely linked to coat color on Chromosome 4. To investigate the effect of a particular Tlr4 mutation on LPS response, three experiments were performed following a cross between fully responsive He-N mice [tlr4(+) /tlr4(+) ] and He-J mice homozygous for the mutation [tlr4(d) /tlr4(d) ].Experiment 1Researchers isolated spleen cells for analysis of protein expression and LPS response. In cells isolated from F1 mice, both wild-type and mutant TLRs were distinguishable by protein electrophoresis. Following this first analysis, spleen cells from each cohort were exposed to 2 × 10⁵ SRC, an antigen formed by sheep erythrocytes. Cultures were then incubated in the presence or absence of Ph-LPS, with LPS extracted from Escherichia coli K345 cells using a phenol-water mixture. Titers of anti-SRC antibody were recorded on incubation day 5, with the results shown in Table 1.Table 1 Mean anti-SRC titers with standard error
Experiment 2Serum samples were assayed for interferon production 2 hours post LPS injection. Interferon was quantified using a plaque reduction assay on mouse cells challenged with vesicular stomatitis virus.
Figure 1 Average serum interferon levels in mice cohortsExperiment 3Mice were injected with varying doses of Ph-LPS and monitored for 4 days. The lethal dose (LD₅₀) was defined as the minimum dose causing death in 50% of injected mice. Compared to He-N mice, results reflected a 10-fold increase in LD₅₀ for F1 mice and a 100-fold increase in LD₅₀ for He-J mice.
-In an isolated population of 10,000 mice, 1,600 are homozygous for a Tlr4 defect. Assuming stable allele and genotype frequencies, how many mice are heterozygous for a Tlr4 defect?

Question

Passage
Lipopolysaccharides (LPS) found in gram-negative bacterial cells can elicit a lethal degree of adjuvanticity, or immune activation, in LPS-responsive host organisms. In mice, responses may be modulated by abnormalities in the toll-like receptor (TLR) encoded by the Tlr4 gene closely linked to coat color on Chromosome 4. To investigate the effect of a particular Tlr4 mutation on LPS response, three experiments were performed following a cross between fully responsive He-N mice [tlr4(+) /tlr4(+) ] and He-J mice homozygous for the mutation [tlr4(d) /tlr4(d) ].Experiment 1Researchers isolated spleen cells for analysis of protein expression and LPS response. In cells isolated from F1 mice, both wild-type and mutant TLRs were distinguishable by protein electrophoresis. Following this first analysis, spleen cells from each cohort were exposed to 2 × 10⁵ SRC, an antigen formed by sheep erythrocytes. Cultures were then incubated in the presence or absence of Ph-LPS, with LPS extracted from Escherichia coli K345 cells using a phenol-water mixture. Titers of anti-SRC antibody were recorded on incubation day 5, with the results shown in Table 1.Table 1 Mean anti-SRC titers with standard error

Experiment 2Serum samples were assayed for interferon production 2 hours post LPS injection. Interferon was quantified using a plaque reduction assay on mouse cells challenged with vesicular stomatitis virus.

Figure 1 Average serum interferon levels in mice cohortsExperiment 3Mice were injected with varying doses of Ph-LPS and monitored for 4 days. The lethal dose (LD₅₀) was defined as the minimum dose causing death in 50% of injected mice. Compared to He-N mice, results reflected a 10-fold increase in LD₅₀ for F1 mice and a 100-fold increase in LD₅₀ for He-J mice.
-In an isolated population of 10,000 mice, 1,600 are homozygous for a Tlr4 defect. Assuming stable allele and genotype frequencies, how many mice are heterozygous for a Tlr4 defect?

Quizplus · Accepted Answer

Allele frequency describes the relative frequency of an allele or gene version within a given population, and genotype frequency reflects the relative frequency of a particular genotype. Usually, these frequencies are described as fractions or percentages. Hardy-Weinberg calculations can be used to relate allele and genotype frequencies in stable, nonevolving populations: p + q = 1: If two versions (alleles) exist for a given gene, respective allele frequencies are commonly denoted as p, which represents the major (most common) allele, and q, which represents the minor (less common) allele. Statistically, the sum of these frequencies must equal 1. p² + 2pq + q² = 1: Genotype frequency can be determined by the probability of inheriting a genotype and is therefore dependent on allele frequencies. The frequency of homozygotes is equal to p² or q² whereas the frequency of heterozygotes is equal to 2pq. In this example, p is the frequency of the normal-functioning Tlr4 allele and q is the frequency of the mutated Tlr4 allele. The frequency of mice homozygous for the mutated allele (q²) is 1,600/10,000, or 0.16. Therefore, q is the square root of 0.16, or 0.40, and this value can be used to calculate p: p = 1 − 0.40 = 0.60 The p and q allele frequencies can then be used to calculate the frequency of the heterozygous genotype and the total number of heterozygous mice in the population of 10,000: 2pq = 2(0.60)(0.40) = 0.48(0.48)(10,000) = 4,800 mice (Choice A) 2,400 is one half of the number of heterozygous mice. Heterozygote frequency is equal to 2 times pq, which is the sum of probabilities of inheriting p from the father and q from the mother (1pq) or p from the mother and q from the father (1pq). (Choice B) 3,600 is equal to the number of mice homozygous for the normal functioning receptor: (10,000)(p²). (Choice D) 5,200 is equal to the number of mice containing at least one copy of the normal allele: (10,000)(p² + 2pq) or (10,000)(1 - q²). Educational objective: Hardy-Weinberg equations can be used to relate allele frequencies and genotype frequencies. Genotype frequencies are equal to the probability of inheriting each genotype, with the frequency of homozygotes equal to p² or q² and the frequency of heterozygotes equal to 2pq.

Passage Lipopolysaccharides (LPS) Found in Gram-Negative Bacterial Cells Can Elicit a a Lethal