During your work as a laboratory assistant in the research facilities of Dr. O. Sophila, a world-famous geneticist, you come across an unusual bottle of fruit flies. All the flies in the bottle appear normal when they are in an incubator set at 22°C. When they are moved to a 30°C incubator, however, a few of the flies slowly become paralyzed; and after about 20 to 30 minutes, they are unable to move. Returning the flies to 22°C restores their ability to move after about 30 to 45 minutes.
With Dr. Sophila's encouragement, you set up 10 individual crosses between single male and female flies that exhibit the unusual behavior. Among 812 progeny, 598 exhibit the unusual behavior and 214 do not. When you leave one of the test bottles in the 30°C incubator too long, you discover that more than 2 hours at high temperature kills the paralyzed flies. When you tell this to Dr. Sophila, he says, 'Aha! I know how to explain this condition.' What is his explanation?

Verified step by step guidance

1. Step 1: Begin by analyzing the observed phenotype. The flies exhibit a temperature-sensitive paralysis phenotype, which is reversible when returned to a lower temperature. This suggests that the condition is likely caused by a mutation in a gene that encodes a protein sensitive to temperature changes.
2. Step 2: Examine the inheritance pattern of the trait. Among the 812 progeny, 598 exhibit the unusual behavior (temperature-sensitive paralysis) and 214 do not. Calculate the ratio of affected to unaffected flies to determine if the trait follows Mendelian inheritance patterns, such as dominant or recessive inheritance.
3. Step 3: Consider the lethality observed at high temperatures. The fact that prolonged exposure to 30°C kills the paralyzed flies suggests that the mutation may affect a critical protein required for survival at elevated temperatures. This could indicate a loss-of-function mutation in a gene involved in neural or muscular function.
4. Step 4: Hypothesize the genetic basis of the condition. Based on the data, the condition could be caused by a single-gene mutation that is either autosomal or sex-linked. The observed ratio of affected to unaffected progeny can help determine whether the mutation is dominant or recessive.
5. Step 5: Conclude with Dr. Sophila's likely explanation. He might propose that the condition is due to a temperature-sensitive mutation in a gene encoding a protein essential for neural or muscular activity. At high temperatures, the protein misfolds or becomes nonfunctional, leading to paralysis. Returning to a lower temperature allows the protein to refold and restore function.

Key Concepts

Temperature Sensitivity in Genetics

Temperature sensitivity refers to how certain genetic traits can be influenced by environmental conditions, such as temperature. In this case, the fruit flies exhibit normal behavior at 22°C but become paralyzed at 30°C, indicating that the gene responsible for their movement may be temperature-sensitive, affecting protein function or expression under different thermal conditions.

Phenotypic Variation

Phenotypic variation is the observable differences in traits among individuals, which can arise from genetic differences and environmental influences. The progeny of the fruit flies show a clear phenotypic variation, with 598 exhibiting unusual behavior and 214 not, suggesting a genetic basis for the observed traits and the potential for inheritance patterns.

Genetic Inheritance Patterns

Genetic inheritance patterns describe how traits are passed from parents to offspring, often following Mendelian principles. The ratio of progeny exhibiting the unusual behavior suggests a possible dominant or recessive trait, which Dr. Sophila may use to explain the genetic basis of the paralysis observed in the fruit flies under high temperature.