Ch. 25 - Quantitative Genetics and Multifactorial Traits

Klug - Concepts of Genetics 12th Edition

Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook

Klug 12th Edition

Ch. 25 - Quantitative Genetics and Multifactorial Traits

Problem 8

Chapter 25, Problem 8

In the following table, average differences of height, weight, and fingerprint ridge count between monozygotic twins (reared together and apart), dizygotic twins, and nontwin siblings are compared:

Based on the data in this table, which of these quantitative traits has the highest heritability values?

Verified step by step guidance

Step 1: Understand the concept of heritability in this context. Heritability measures the proportion of phenotypic variation in a trait that is due to genetic differences among individuals. Lower average differences between genetically identical individuals (like monozygotic twins) compared to less genetically related individuals (like dizygotic twins or siblings) suggest higher heritability.

Step 2: Compare the average differences for each trait between monozygotic (MZ) twins reared together and apart, dizygotic (DZ) twins reared together, and siblings reared together. Smaller differences in MZ twins relative to DZ twins and siblings indicate stronger genetic influence.

Step 3: For each trait (height, weight, ridge count), observe the pattern of differences: the smaller the difference in MZ twins compared to DZ twins and siblings, the higher the heritability. For example, height shows very small differences in MZ twins (1.7 and 1.8) compared to larger differences in DZ twins (4.4) and siblings (4.5).

Step 4: Note that weight shows a larger difference in MZ twins reared apart (4.5) compared to reared together (1.9), which suggests environmental factors also play a role. Ridge count differences are generally smaller but the difference between MZ and DZ twins is less pronounced.

Step 5: Conclude which trait has the highest heritability by identifying the trait with the greatest difference between MZ twins and DZ twins/siblings, indicating the strongest genetic influence.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Heritability

Heritability measures the proportion of observed variation in a trait among individuals that can be attributed to genetic differences. It ranges from 0 to 1, where higher values indicate a stronger genetic influence. Heritability is often estimated by comparing trait similarities between relatives with different genetic relatedness.

Twin Studies

Twin studies compare monozygotic (MZ) twins, who share nearly 100% of their genes, with dizygotic (DZ) twins, who share about 50%. Differences in trait similarity between these groups help estimate genetic and environmental contributions. MZ twins reared apart provide insight into genetic effects independent of shared environment.

Quantitative Traits and Environmental Influence

Quantitative traits, like height, weight, and fingerprint ridge count, vary continuously and are influenced by multiple genes and environmental factors. Comparing trait differences among relatives reared together or apart helps distinguish genetic effects from environmental ones, clarifying the trait's heritability.

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Related Practice

Textbook Question

An inbred strain of plants has a mean height of 24 cm. A second strain of the same species from a different geographic region also has a mean height of 24 cm. When plants from the two strains are crossed together, the F₁ plants are the same height as the parent plants. However, the F₂ generation shows a wide range of heights; the majority are like the P₁ and F₁ plants, but approximately 4 of 1000 are only 12 cm high and about 4 of 1000 are 36 cm high.

Indicate three possible genotypes that could account for F₂ plants that are 18 cm high and three that account for F₂ plants that are 33 cm high.

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Textbook Question

Erma and Harvey were a compatible barnyard pair, but a curious sight. Harvey's tail was only 6 cm long, while Erma's was 30 cm. Their F₁ piglet offspring all grew tails that were 18 cm. When inbred, an F₂ generation resulted in many piglets (Erma and Harvey's grandpigs), whose tails ranged in 4-cm intervals from 6 to 30 cm (6, 10, 14, 18, 22, 26, and 30). Most had 18-cm tails, while 1/64 had 6-cm tails and 1/64 had 30-cm tails.

Explain how these tail lengths were inherited by describing the mode of inheritance, indicating how many gene pairs were at work, and designating the genotypes of Harvey, Erma, and their 18-cm-tail offspring.

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Textbook Question

If one of the 18-cm-tail F₁ pigs is mated with one of the 6-cm-tail F₂ pigs, what phenotypic ratio will be predicted if many offspring resulted? Diagram the cross.

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Textbook Question

What kind of heritability estimates (broad sense or narrow sense) are obtained from human twin studies?

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Textbook Question

List as many human traits as you can that are likely to be under the control of a polygenic mode of inheritance.

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Textbook Question

Corn plants from a test plot are measured, and the distribution of heights at 10-cm intervals is recorded in the following table:

Height (cm) Plants (no.)

100 20

110 60

120 90

130 130

140 180

150 120

160 70

170 50

180 40

Calculate

(a) the mean height,

(b) the variance,

(d) the standard error of the mean.

Plot a rough graph of plant height against frequency. Do the values represent a normal distribution? Based on your calculations, how would you assess the variation within this population?

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