Ch. 3 - Cell Division and Chromosome Heredity

Sanders - Genetic Analysis: An Integrated Approach 3rd Edition

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Sanders 3rd Edition

Ch. 3 - Cell Division and Chromosome Heredity

Problem 27

Chapter 3, Problem 27

In an 1889 book titled Natural Inheritance (Macmillan, New York), Francis Galton, who investigated the inheritance of measurable (quantitative) traits, formulated a law of 'ancestral inheritance.' The law stated that individuals inherit approximately one-half of their genetic traits from each parent, about one-quarter of the traits from each grandparent, one-eighth from each great grandparent, and so on. In light of the chromosome theory of heredity, argue either in favor of Galton's law or against it.

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Understand Galton's law of 'ancestral inheritance,' which suggests that genetic traits are inherited in diminishing proportions from ancestors: 1/2 from parents, 1/4 from grandparents, 1/8 from great-grandparents, and so on.

Recall the chromosome theory of heredity, which states that genes are located on chromosomes and are passed from parents to offspring through gametes during reproduction.

Consider the mechanism of Mendelian inheritance, where offspring inherit one allele for each gene from each parent, resulting in a 50% genetic contribution from each parent. This aligns with the first part of Galton's law.

Evaluate the diminishing contributions from more distant ancestors. While Galton's law suggests a mathematical reduction in genetic influence, the chromosome theory indicates that recombination and independent assortment during meiosis shuffle genetic material, making distant ancestral contributions less predictable and not strictly proportional.

Conclude that while Galton's law provides a simplified mathematical model of inheritance, it does not fully account for the complexities of genetic recombination, linkage, and the random nature of allele segregation described by the chromosome theory of heredity.

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Key Concepts

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

Chromosome Theory of Heredity

The chromosome theory of heredity posits that genes are located on chromosomes, which are passed from parents to offspring during reproduction. This theory explains how traits are inherited through the segregation and independent assortment of chromosomes during meiosis. It provides a genetic basis for understanding inheritance patterns, supporting the idea that traits are not simply averaged from parents but are inherited in specific combinations.

Quantitative Traits

Quantitative traits are characteristics that are influenced by multiple genes and can be measured on a continuous scale, such as height or weight. These traits often exhibit a normal distribution in a population, reflecting the additive effects of many alleles. Understanding quantitative traits is essential for evaluating Galton's law, as it suggests that inheritance is more complex than a simple halving of traits from parents.

Ancestral Inheritance

Ancestral inheritance refers to the concept that traits are passed down through generations in a predictable manner, as proposed by Galton. His law suggests a geometric distribution of genetic contribution from ancestors, which may oversimplify the actual genetic mechanisms at play. This concept is challenged by modern genetics, which recognizes that inheritance is influenced by recombination, mutations, and the complex interactions of multiple genes.

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Related Practice

Textbook Question

A wild-type Drosophila male and female are crossed, producing 324 female progeny and 161 male progeny. All their progeny are wild type.

Propose a genetic hypothesis to explain these data.

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Textbook Question

In Drosophila, the X-linked echinus eye phenotype disrupts formation of facets and is recessive to wild-type eye. Autosomal recessive traits vestigial wing and ebony body assort independently of one another. Examine the progeny from the three crosses shown below, and identify the genotype of parents in each cross.

Textbook Question

In humans, SRY is located near a pseudoautosomal region (PAR) of the Y chromosome, a region of homology between the X and Y chromosomes that allows them to synapse during meiosis in males and is a region of crossover between the chromosomes. The diagram below shows SRY in relation to the pseudoautosomal region.

About 1 in every 25,000 newborn infants is born with sex reversal; the infant is either an apparent male but with two X chromosomes or an apparent female but with an X and a Y chromosome. Explain the origin of sex reversal in human males and females involving the SRY gene. (Hint: See Experimental Insight 3.1 for a clue about the mutational mechanism.)

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Textbook Question

Lesch–Nyhan syndrome (OMIM 300322) is a rare X-linked recessive disorder that produces severe mental retardation, spastic cerebral palsy, and self-mutilation.

What is the probability that the first son of a man whose brother has Lesch–Nyhan syndrome will be affected?

Textbook Question

A wild-type Drosophila male and female are crossed, producing 324 female progeny and 161 male progeny. All their progeny are wild type.

Design an experiment that will test your hypothesis, using the wild-type progeny identified above. Describe the results you expect if your hypothesis is true.

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Textbook Question

Lesch–Nyhan syndrome (OMIM 300322) is a rare X-linked recessive disorder that produces severe mental retardation, spastic cerebral palsy, and self-mutilation.

If the first son of the woman described in (a) is affected, what is the probability that her second son is affected?

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