Ch. 19 - Genetic Analysis of Quantitative Traits

Sanders - Genetic Analysis: An Integrated Approach 3rd Edition

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Sanders 3rd Edition

Ch. 19 - Genetic Analysis of Quantitative Traits

Problem 26a

Chapter 19, Problem 26a

The children of couples in which one partner has blood type O (genotype ii) and the other partner has blood type AB (genotype IᴬIᴮ) are studied. What is the expected concordance rate for blood type of MZ twins in this study? Explain your answer.

Verified step by step guidance

Determine the possible genotypes of the offspring by performing a Punnett square for the cross between one parent with genotype ii (blood type O) and the other parent with genotype IᴬIᴮ (blood type AB).

Set up the Punnett square: Place the alleles from the ii parent (i, i) on one side and the alleles from the IᴬIᴮ parent (Iᴬ, Iᴮ) on the other side. Fill in the grid to determine the offspring genotypes.

Analyze the results of the Punnett square. The possible genotypes of the offspring will be Iᴬi and Iᴮi, corresponding to blood types A and B, respectively. Note that no offspring will have blood type O or AB in this cross.

Understand the concept of concordance rate in monozygotic (MZ) twins. MZ twins are genetically identical, so they will always have the same genotype and, therefore, the same blood type. This means the concordance rate for blood type in MZ twins is 100%.

Conclude that since MZ twins share identical genotypes, the expected concordance rate for blood type in this study is 100%, regardless of whether the offspring have blood type A (Iᴬi) or blood type B (Iᴮi).

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Key Concepts

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

Blood Type Inheritance

Blood type is determined by the ABO gene, which has three alleles: A (Iᴬ), B (Iᴮ), and O (i). Individuals with blood type O have the genotype ii, while those with blood type AB have the genotype IᴬIᴮ. The offspring of these parents can inherit one allele from each parent, leading to potential blood types A (Iᴬi) or B (Iᴮi), but not O or AB.

Monozygotic (MZ) Twins

Monozygotic twins, or identical twins, arise from a single fertilized egg that splits into two embryos. They share 100% of their genetic material, which means that any genetic traits, including blood type, will be concordant. In this context, the study of MZ twins helps to understand the genetic basis of blood type inheritance.

Concordance Rate

Concordance rate refers to the probability that both twins in a pair exhibit the same trait or condition. In the case of MZ twins, the concordance rate for blood type would be expected to be high, as they share identical genetic information. Given the blood types possible from the parents, the expected concordance rate for MZ twins in this study would be 100% for the blood types A and B.

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Textbook Question

Cattle breeders would like to improve the protein content and butterfat content of milk produced by a herd of cows. Narrow sense heritability values are 0.60 for protein content and 0.80 for butterfat content. The average percentages of these traits in the herd and the percentages of the traits in cows selected for breeding are as follows. Trait Herd Average Selected Cows Protein content 20.2% 22.7% Butterfat content 6.5% 7.4% Which trait is likely to be the most responsive to artificial selection applied by the cattle breeders through selection of cows for mating?

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Textbook Question

In human gestational development, abnormalities of the closure of the lower part of the mid-face can result in cleft lip, if the lip alone is affected by the closure defect, or in cleft lip and palate (the roof of the mouth), if the closure defect is more extensive. Cleft lip and cleft lip with cleft palate are multifactorial disorders that are threshold traits. A family with a history of either condition has a significantly increased chance of a recurrence of mid-face cleft disorder in comparison with families without such a history. However, the recurrence risk of a mid-face cleft disorder is higher in families with a history of cleft lip with cleft palate than in families with a history of cleft lip alone. Suppose a friend of yours who has not taken genetics asks you to explain these observations. Construct a genetic explanation for the increased recurrence risk of mid-face clefting in families that have a history of cleft disorders versus families without a history of such disorders.

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Textbook Question

In human gestational development, abnormalities of the closure of the lower part of the mid-face can result in cleft lip, if the lip alone is affected by the closure defect, or in cleft lip and palate (the roof of the mouth), if the closure defect is more extensive. Cleft lip and cleft lip with cleft palate are multifactorial disorders that are threshold traits. A family with a history of either condition has a significantly increased chance of a recurrence of mid-face cleft disorder in comparison with families without such a history. However, the recurrence risk of a mid-face cleft disorder is higher in families with a history of cleft lip with cleft palate than in families with a history of cleft lip alone. Construct a similar explanation of why the recurrence risk of a cleft disorder is higher in families with a history of cleft lip with cleft palate than in families with a history of cleft lip alone.

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Textbook Question

The children of couples in which one partner has blood type O (genotype ii) and the other partner has blood type AB (genotype IᴬIᴮ) are studied. What is the expected concordance rate for blood type of DZ twins in this study? Explain why this answer is different from the answer to part (a).

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Textbook Question

Answer the following in regard to multifactorial traits in human twins. If the trait is substantially influenced by genes, would you expect the concordance rate to be higher in MZ twins or higher in DZ twins? Explain your reasoning.

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Textbook Question

Answer the following in regard to multifactorial traits in human twins. If the trait is produced with little contribution from genetic variation, what would you expect to see if you compared the concordance rates of MZ twins versus DZ twins? Explain your reasoning.

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