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

1. 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.
2. 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.
3. 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.
4. 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.
5. 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.

Key Concepts

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.