Question

In four o'clock plants, many flower colors are observed. In a cross involving two true-breeding strains, one crimson and the other white, all of the \(F_{1}\) generation were rose color. In the \(F_{2}\) four new phenotypes appeared along with the \(P_{1}\) and \(F_{1}\) parental colors. The following ratio was obtained: Propose an explanation for the inheritance of these flower colors.

Short answer

The inheritance of flower colors in the cross between the true-breeding strains of four o'clock plants can be explained through the interaction of two independently inherited gene pairs (A and a; B and b). Crimson (AABB) and white (aabb) parents cross resulting in all F1 progeny being heterozygous (AaBb) with rose color flowers. Upon self-pollination of F1 progeny, the F2 generation shows a ratio of 1 crimson: 4 rose: 6 evening: 4 pink: 1 white, as determined by various combinations of the gene pairs A, a, B, and b. The principles of Mendelian genetics, such as the laws of segregation and independent assortment, help explain this inheritance pattern.

Step-by-step solution

Understand the inheritance pattern

We are given a cross between two true-breeding strains, one with crimson flowers and the other with white flowers. All of the F1 generation were rose color. This indicates that there is at least partial dominance of one trait over the other (crimson flower color partially dominates white flower color). In the F2 generation, different phenotypes appeared along with the parental colors. This suggests that there might be a more complex interaction between the genes than simple dominance.

Analyze the given ratio

The given ratio in the F2 generation is 1 crimson:4 rose:6 evening:4 pink:1 white. We can match these phenotypes to gene combinations using the law of segregation and the law of independent assortment. It seems that there might be two gene loci that are involved in the determination of flower color. Let's assume the two loci are A and B. The crimson phenotype can be coded as AABB, the white phenotype as aabb. Now we need to find the genotypes for rose, evening, and pink flower colors considering the mixture of alleles.

Propose a theoretical explanation

Based on the given ratio, we can propose an explanation using a hypothesis of gene interactions. We can assume that the color of flowers is determined by the interaction of two independently inherited gene pairs (A and a; B and b). The crimson parent (AABB) and the white parent (aabb) cross, and all the F1 progeny are heterozygous for both gene pairs (AaBb) and produce rose color flowers. Next, the F1 rose plants (AaBb) are allowed to self-pollinate, and the F2 progeny will have the following genotypes and phenotypes: - AABB: 1/16 crimson - AABb, AaBB, AAbb, aaBB: 4/16 rose - AaBb: 6/16 evening - Aabb, aabb, aaBb: 4/16 pink - aabb: 1/16 white The ratio in the F2 generation is 1 crimson: 4 rose: 6 evening: 4 pink: 1 white, as observed in the exercise. Using the principles of Mendelian genetics, we were able to explain the inheritance of flower colors in this cross.

Key concepts

Flower Color Inheritance

In the world of Mendelian genetics, flower color inheritance can be a fascinating example to study, especially in plants like the four o'clock plant. When looking at the inheritance of flower colors across generations, as investigated in a cross between two true-breeding strains, we can identify patterns that point towards genetic interactions. These two strains, one crimson and the other white, were crossed, resulting in all of the first generation ( F_1 ) flowers being rose-colored. This observed rose color is a clear indication of partial dominance, or incomplete dominance, where neither crimson nor white completely overshadows the other. Partial dominance is crucial because it allows for the blending of traits, presenting a third intermediate phenotype that is distinct from either parent. In the F_2 generation, where the F_1 rose flowers were self-pollinated, a variety of phenotypes, including new colors like evening and pink, emerged alongside the previously existing crimson, rose, and white. This pattern of inheritance illustrates that flower color in the four o'clock plant is likely controlled by two gene loci, showing more complexity than simple single-gene inheritance. Understanding this can help solidify the concept of polygenic inheritance in Mendelian genetics, where multiple genes can affect a single trait.

Gene Interaction

Gene interaction is an essential aspect of Mendelian genetics that can significantly impact phenotypic outcomes, such as flower color in the four o'clock plant. In the exercise, the F_1 generation flowers all shared the rose color, indicating a genetic interaction between genes at different loci. When analyzing the F_2 generation, different phenotypes emerged, suggesting that multiple genetic factors were at work. The proposed explanation involved two gene loci, labeled as A and B. These loci interact to determine the resulting flower color. For instance:

• Crimson flowers may be encoded as AABB , which occurs when both loci have dominant alleles.
• White flowers may be aabb , with both loci containing recessive alleles.
• AaBb produces rose flowers, a blend of the crimson and white traits due to the combination of dominant and recessive alleles.

Such interactions illustrate that genes do not always act independently in determining a phenotype. Instead, they can enhance, suppress, or modify each other's effects, leading to a spectrum of phenotypic expressions observed in the F2 generation. Understanding gene interaction helps explain why we see more than just the parental phenotypes and supports the idea that some traits are influenced by a more complex network of genetic interactions.

Independent Assortment

Independent assortment is a fundamental principle of Mendelian genetics that explains how genes are inherited independently of each other if located on different chromosomes. This principle becomes evident in the inheritance patterns seen in the four o'clock plant exercise. When exploring the F_2 generation, the unique ratio of phenotypes—1 crimson: 4 rose: 6 evening: 4 pink: 1 white—reveals an underlying principle involving multiple genes assorting independently. During the production of gametes in the F_1 generation, each pair of alleles (A and a; B and b) segregates independently. This results in a variety of allele combinations in the offspring, showcasing how independent assortment can lead to new phenotypes that were not present in the parents, such as the evening and pink flower colors. For example:

• A gamete could carry the A allele alongside B, a, or b, leading to different possible zygotes when mixed with other gametes.
• This mixing follows a pattern that fits a Mendelian ratio resulting from the independent assortment of genes.

By helping to generate genetic diversity, independent assortment is a key mechanism in evolution and variation. It provides the raw material for selection to act upon, allowing populations to adapt to changing environments. In the case of flower colors, it helps explain the appearance of multiple distinct flower colors from crosses between two initial parent strains.