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Chapter 19: Problem 25

In a population of Drosophila melanogaster reared in the laboratory, the mean wing length is \(0.55 \mathrm{mm}\) and the range is 0.35 to \(0.65 .\) A geneticist selects a female with wings that are \(0.42 \mathrm{mm}\) in length and mates her with a male that has wings that are \(0.56 \mathrm{mm}\) in length. a. What is the expected wing length of their offspring if wing length has a narrow-sense heritability of \(1.0 ?\) b. What is the expected wing length of their offspring if wing length has a narrow-sense heritability of \(0.0 ?\)

Short Answer

Expert verified
a. 0.49 mm; b. 0.55 mm

Step by step solution

01

Understanding narrow-sense heritability

Narrow-sense heritability indicates the proportion of variance in a trait that is due to additive genetic factors. A heritability of 1.0 means that the offspring's traits are determined completely by the additive effects of the parents鈥� genes, whereas a heritability of 0.0 means they are determined entirely by environmental effects.
02

Calculate the average phenotype of the parents

To find the average phenotype of the parents, calculate the mean of the father's and mother's wing lengths. The mother's wings are 0.42 mm, and the father's wings are 0.56 mm. The average is computed as follows: \[ \text{Average Wing Length of Parents} = \frac{0.42 + 0.56}{2} \] Simplifying, we find:\[ \frac{0.42 + 0.56}{2} = \frac{0.98}{2} = 0.49 \text{ mm} \]
03

Calculate the expected offspring wing length for heritability of 1.0

With a heritability of 1.0, the offspring's expected trait is the exact average of the parents' traits due to purely genetic influences. Therefore, the expected wing length is:\[ 0.49 \text{ mm} \]
04

Calculate the expected offspring wing length for heritability of 0.0

With a heritability of 0.0, the offspring's trait is influenced entirely by the environment, and the trait will converge to the population mean. Therefore, since the mean wing length of the population is 0.55 mm, the expected offspring wing length is:\[ 0.55 \text{ mm} \]

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Drosophila melanogaster
Drosophila melanogaster, commonly known as the fruit fly, is a small fly species that plays a pivotal role in genetic research. This species is favored in laboratory settings due to several practical traits:
  • They have a short life cycle, taking only about 10 days to develop from egg to adult.
  • They produce a large number of offspring, allowing for statistical analysis of genetic data.
  • Their genetic makeup is relatively simple yet remarkably similar to that of humans, which makes insights relevant to understanding human genetics.
  • They are inexpensive to maintain, further enhancing their utility in research environments.
These characteristics make Drosophila melanogaster ideal for studies involving inheritance patterns, phenotypic expressions, and various genetic factors. The fruit fly's vast contribution to genetics includes understanding mutations, mapping genes, and studying genetic interactions.
Wing Length
Wing length in Drosophila melanogaster is a significant quantitative trait often examined to understand genetic inheritance. Several factors influence wing length:
  • Genetic factors: Wing length can be inherited through genetic material passed from parents to offspring.
  • Environmental conditions: Factors such as temperature and nutrition during the developmental stages can also affect wing length.
In laboratory conditions, scientists can control many environmental variables, allowing them to focus on genetic contributions to traits like wing length. Analyzing wing length is a way to evaluate heritability 鈥� the extent to which genetic factors affect this trait. Researchers use wing length measurements in various experiments to explore the balance between genetic inheritance and environmental influence, which can provide insights into broader genetic concepts.
Additive Genetic Factors
Additive genetic factors refer to the individual contributions that alleles at different genes make to a phenotype. These factors are responsible for the resemblance between parents and offspring in traits like wing length. When discussing narrow-sense heritability, we focus on these additive effects because they predict how a trait will respond to selection. Here's how it works:
  • Each allele either increases or decreases wing length by a certain amount, depending on its nature.
  • These effects add up (hence "additive") to determine the overall genetic potential for a trait in the offspring.
  • In cases where narrow-sense heritability is 1.0, additive genetic factors completely determine the trait in question.
This concept is crucial in selective breeding programs and understanding evolutionary processes, as it helps predict how traits will be passed on through generations. By examining additive genetic factors, scientists can manipulate and predict changes in populations over time.

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Most popular questions from this chapter

In a sample of adult women from the United States, the average height was \(164.4 \mathrm{cm}\) and the standard deviation was \(6.2 \mathrm{cm} .\) Women who are more than 2 standard deviations above the mean are considered very tall, and women who are more than 2 standard deviations below the mean are considered very short. Height in women is normally distributed. a. What are the heights of very tall and very short women? b. In a population of 10,000 women, how many are expected to be very tall and how many very short?

Question 26 refers to QTL on the cricket autosomes. For the sex chromosomes, females crickets are XX and males crickets are \(\mathrm{XO}\), having just one \(\mathrm{X}\) chromosome but no Y chromosome. Can QTL for pulse rate be mapped on cricket X chromosomes? If the song is only sung by male crickets, can the dominance effects of QTL on the X be estimated?

A chicken breeder is working with a population in which the mean number of eggs laid per hen in one month is 28 and the variance is 5 eggs \(^{2}\). The narrow-sense heritability is known to be 0.8 . Given this information, can the breeder expect that the population will respond to selection for an increase in the number of eggs per hen in the next generation? a. No, applying selection is always risky and a breeder never knows what to expect. b. No, a breeder needs to know the broad-sense heritability to know what to expect. c. Yes, since the narrow-sense heritability is close to \(1(0.8),\) then we would expect selective breeding could lead to increased egg production in the next generation. d. Yes, since the variance is greater than 0 e. Both c and d are correct.

Suppose that the mean IQ in the United States is roughly 100 and the standard deviation is 15 points. People with IQs of 145 or higher are considered "geniuses" on some scales of measurement. What percentage of the population is expected to have an IQ of 145 or higher? In a country with 300 million people, how many geniuses are there expected to be?

Maize plants in a population are on average \(180 \mathrm{cm}\) tall. Narrow- sense heritability for plant height in this population is \(0.5 .\) A breeder selects plants that are \(10 \mathrm{cm}\) taller on average than the population mean to produce the next generation, and the breeder continues applying this level of selection for eight generations. What will be the average height of the plants after eight generations of selection? Assume that \(h^{2}\) remains 0.5 and \(V_{e}\) does not change over the course of the experiment.
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