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Ch. 25 - Quantitative Genetics and Multifactorial Traits
All textbooksKlug 12th EditionCh. 25 - Quantitative Genetics and Multifactorial TraitsProblem 8
Chapter 24, 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:   Trait            MZ Reared    MZ        DZ Reared   Sibs Reared                     Together      Reared     Together       Together                                          Apart                                              _Height (cm)      1.7              1.8             4.4                4.5 Weight (kg)      1.9               4.5            4.5                4.7 Ridge count     0.7               0.6            2.4                 2.7 Based on the data in this table, which of these quantitative traits has the highest heritability values?

Verified step by step guidance
1
Understand that heritability is a measure of how much of the variation in a trait can be attributed to genetic differences.
Recognize that monozygotic (MZ) twins share 100% of their genes, while dizygotic (DZ) twins share about 50%, similar to nontwin siblings.
Note that if a trait has high heritability, MZ twins reared apart should have similar trait values, indicating genetic influence.
Compare the differences in trait values between MZ twins reared apart and DZ twins or siblings reared together for each trait.
Identify the trait with the smallest difference between MZ twins reared apart, as this suggests the highest genetic influence and thus the highest heritability.

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Key Concepts

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

Heritability

Heritability is a measure that estimates the proportion of variation in a trait that can be attributed to genetic differences among individuals in a population. It is expressed as a value between 0 and 1, where 0 indicates no genetic contribution and 1 indicates complete genetic determination. Understanding heritability helps in assessing the extent to which genetics influence traits like height, weight, and fingerprint ridge count.
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Calculating Heritability

Monozygotic vs. Dizygotic Twins

Monozygotic (MZ) twins originate from a single fertilized egg and share nearly identical genetic material, while dizygotic (DZ) twins come from two separate eggs and share about 50% of their genes, similar to regular siblings. Comparing traits between MZ and DZ twins allows researchers to infer the genetic versus environmental contributions to those traits, as MZ twins are expected to show more similarity due to their shared genetics.
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Quantitative Traits

Quantitative traits are characteristics that can be measured and quantified, such as height, weight, and fingerprint ridge count. These traits typically exhibit continuous variation and are influenced by multiple genes and environmental factors. Analyzing the differences in these traits among various sibling types helps in understanding the genetic basis and heritability of these traits.
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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.

How many gene pairs are involved?

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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

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. 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, 

(c) the standard deviation, and 

(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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