Ch. 9 - Extranuclear Inheritance

Klug - Concepts of Genetics 12th Edition

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

Klug 12th Edition

Ch. 9 - Extranuclear Inheritance

Problem 4

Chapter 9, Problem 4

A plant may have green, white, or green-and-white (variegated) leaves on its branches, owing to a mutation in the chloroplast that prevents color from developing. Predict the results of the following crosses:

  Ovule Source        Pollen Source
(a) Green branch    x  White branch
(b) White branch     x  Green branch
(c) Variegated branch x  Green branch
(d) Green branch    x  Variegated branch

Verified step by step guidance

Understand that the inheritance of chloroplast traits is typically maternal, meaning the phenotype of the offspring is determined by the ovule source (the maternal parent). Chloroplasts are inherited through the cytoplasm of the egg cell, not the pollen.

For cross (a), where the ovule source is a green branch and the pollen source is a white branch, predict the offspring phenotype based on the maternal (ovule) source. Since the ovule source is green, the offspring will inherit green chloroplasts.

For cross (b), where the ovule source is a white branch and the pollen source is a green branch, predict the offspring phenotype based on the maternal (ovule) source. Since the ovule source is white, the offspring will inherit white chloroplasts.

For cross (c), where the ovule source is a variegated branch and the pollen source is a green branch, predict the offspring phenotype based on the maternal (ovule) source. Variegated branches contain a mix of green and white chloroplasts, so the offspring may inherit green, white, or variegated phenotypes depending on which chloroplasts are passed on.

For cross (d), where the ovule source is a green branch and the pollen source is a variegated branch, predict the offspring phenotype based on the maternal (ovule) source. Since the ovule source is green, the offspring will inherit green chloroplasts.

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Key Concepts

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

Chloroplast Mutations

Chloroplast mutations can affect the pigmentation of plant leaves, leading to variations such as green, white, or variegated leaves. These mutations can disrupt the normal function of chlorophyll production, which is essential for photosynthesis and leaf coloration. Understanding how these mutations occur and their inheritance patterns is crucial for predicting the outcomes of plant crosses.

Genetic Crosses and Punnett Squares

Genetic crosses involve mating two parent plants to observe the inheritance of traits in their offspring. Punnett squares are a tool used to predict the genotypic and phenotypic ratios of the offspring based on the alleles contributed by each parent. This method helps visualize the potential outcomes of crosses, such as those involving different leaf colors in plants.

Phenotypic Ratios

Phenotypic ratios represent the relative frequencies of different observable traits in the offspring resulting from a genetic cross. In the context of the given question, understanding how to calculate these ratios based on the combinations of green, white, and variegated leaves will help predict the appearance of the next generation. This concept is essential for interpreting the results of the crosses described.

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Related Practice

Textbook Question

Write a short essay that distinguishes between organelle heredity and maternal effect.

Textbook Question

Streptomycin resistance in Chlamydomonas may result from a mutation in either a chloroplast gene or a nuclear gene. What phenotypic results would occur in a cross between a member of an mt⁺ strain resistant in both genes and a member of a strain sensitive to the antibiotic? What results would occur in the reciprocal cross?

Textbook Question

Predict the results of a cross between ascospores from a segregational petite strain and a neutral petite strain. Indicate the phenotype of the zygote and the ascospores it may subsequently produce.

Textbook Question

In the discussion, we focused on extranuclear inheritance and how traits can be determined by genetic information contained in mitochondria and chloroplasts, and we discussed how expression of maternal genotypes can affect the phenotype of an organism. At the same time, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, what answers would you propose to the following fundamental questions?

What findings demonstrate a maternal effect as the basis of a mode of inheritance?

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Textbook Question

In diploid yeast strains, sporulation and subsequent meiosis can produce haploid ascospores, which may fuse to reestablish diploid cells. When ascospores from a segregational petite strain fuse with those of a normal wild-type strain, the diploid zygotes are all normal. Following meiosis, ascospores are petite and normal. Is the segregational petite phenotype inherited as a dominant or a recessive trait?

Textbook Question

In a cross of Lymnaea, the snail contributing the eggs was dextral but of unknown genotype. Both the genotype and the phenotype of the other snail are unknown. All F₁ offspring exhibited dextral coiling. Ten of the F₁ snails were allowed to undergo self-fertilization. One-half produced only dextrally coiled offspring, whereas the other half produced only sinistrally coiled offspring. What were the genotypes of the original parents?