91Ó°ÊÓ

The petals of the plant Collinsia parviflora are normally blue, giving the species its common name, blue-eyed Mary. Two pure-breeding lines were obtained from color variants found in nature; the first line had pink petals, and the second line had white petals. The following crosses were made between pure lines, with the results shown: $$\begin{array}{ccl} \text { Parents } & \mathrm{F}_{1} & \mathrm{F}_{2} \\ \hline \text { blue } \times \text { white } & \text { blue } & 101 \text { blue, } 33 \text { white } \\ \text { blue } \times \text { pink } & \text { blue } & 192 \text { blue, } 63 \text { pink } \\ \text { pink } \times \text { white } & \text { blue } & 272 \text { blue, } 121 \text { white }, 89 \text { pink } \\ \hline \end{array}$$ a. Explain these results genetically. Define the allele symbols that you use, and show the genetic constitution of the parents, the \(\mathrm{F}_{1},\) and the \(\mathrm{F}_{2}\) in each cross. b. \(A\) cross between a certain blue \(F_{2}\) plant and a certain white \(\mathrm{F}_{2}\) plant gave progeny of which \(\frac{3}{8}\) were blue, \(\frac{1}{8}\) were pink, and \(\frac{1}{2}\) were white. What must the genotypes of these two \(\mathrm{F}_{2}\) plants have been?

Step by step solution

01

Determine Allele Symbols and Genetic Basis

Let's assume two genes are involved in petal color. Let the alleles be:- Allele \( B \): Blue (dominant for color presence, regardless of shade)- Allele \( b \): Non-blue (absence of blue pigmentation)- Allele \( P \): Pink (dominant within non-blue, making pink petals if no \( B \) is present)- Allele \( p \): Non-pink (absence of pink pigmentation, resulting in white petals if neither \( B \) nor \( P \) is present)Here, blue is dominant over the other colors because in all crosses where blue is involved, the \( F_1 \) generation shows blue petals.

02

Analyze Crosses and Genotypes

For each cross:1. **Blue × White**: - Parental generation: \( B ext{--}P ext{--} \times ext{bbpp} \) - \( F_1 \): All are \( B ext{--}P ext{--} \) (blue) - \( F_2 \): Segregates to roughly 3:1 blue to white, indicating genotypes \( B ext{--} ext{(blue)} \) and \( b ext{--}pp ext{(white)} \)2. **Blue × Pink**: - Parental generation: \( B ext{--}P ext{--} \times ext{bbP ext{--}} \) - \( F_1 \): All are \( B ext{--}P ext{--} \) (blue) - \( F_2 \): Segregation of roughly 3:1 blue to pink suggests pink individuals \( bbP ext{--} \)3. **Pink × White**: - Parental generation: \( bbP ext{--} \times ext{bbpp} \) - \( F_1 \): All are \( B ext{--}P ext{--} \) (blue) due to dominant expression - \( F_2 \): Mix of blue, white, and pink, requiring heterozygosity in both alleles within \( F_1 \) (e.g., \( BbPp \)).

03

Determine Genotypes of F2 Blue and White

In the cross between a blue \( F_2 \) and a white \( F_2 \) plant resulting in progeny:- \( \frac{3}{8} \) blue, \( \frac{1}{8} \) pink, and \( \frac{1}{2} \) white:The resulting progeny ratio suggests:- The blue \( F_2 \) parent must be \( BbPp \) to produce all three phenotypes.- The white \( F_2 \) parent must be \( bbpp \) to produce white and non-blue colored offspring.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Allele Symbols

When delving into genetics, especially the inheritance patterns in plants, the primary building blocks are the alleles. Alleles are different versions of a gene, and determining the symbols for these alleles is fundamental. In studying the petal colors in Collinsia parviflora, we have identified two genes impacting petal color presence and variation. The first allele, labeled as \( B \), signifies a dominant gene for blue pigmentation. This blue allele is dominant, meaning it will express itself over others when present in the genotype. In contrast, the allele \( b \) indicates an absence of blue color; thus, is recessive. Now, when considering pink color expression, we employ another set of symbols: \( P \) and \( p \). Here, \( P \) is dominant and responsible for pink petal expression, but only in the absence of \( B \). Lastly, the allele \( p \) indicates the presence of white color, expressed only in the absence of both \( B \) and \( P \). By understanding these symbols, we can effectively predict and interpret genetic outcomes in crossbreeding scenarios.

Genotype Analysis

Conducting genotype analysis allows us to uncover the genetic makeup behind each phenotype observed. Let's take a closer look at the genotypes in different parental crosses and offspring generations in the Collinsia parviflora study. For the cross between blue and white individuals, the parental genotypes are \( B--P-- \) and \( bbpp \). The resulting \( F_1 \) generation showcases all blue offspring due to the dominant \( B \) allele. In the \( F_2 \) generation, the presence of \( B \) maintains a blue phenotype, while the homozygous recessive combination \( bbpp \) manifests as white.

Similarly, in a blue to pink cross, we start with \( B--P-- \) and \( bbP-- \) parents, resulting again in blue offspring in the \( F_1 \) generation. The subsequent \( F_2 \) generation presents a 3:1 blue to pink ratio, indicating \( BbP-- \) as the pink genotype.

• Blue is expressed in genotypes containing at least one \( B \).
• Pink appears where \( b \) is present along with \( P \), without the \( B \).
• White arises when both \( b \) and \( p \) are present.

This systematic analysis helps in understanding the distribution and probability of each phenotype emerging.

Plant Color Inheritance

Understanding plant color inheritance involves recognizing how certain traits pass from generation to generation. In our context, this inheritance is dictated by the presence or absence of key pigments in Collinsia parviflora. The dominance of the \( B \) allele results in blue petals, overwhelming the expression of other colors. However, the inheritance of color is not solely dependent on one gene.

In instances where \( B \) is absent, the \( P \) allele takes over, impacting petal coloration to be pink. If both \( B \) and \( P \) alleles are missing, \( p \) becomes visible as white petals manifest. Through generations, these color patterns are controlled by Mendelian principles where dominant alleles mask the effects of recessive ones.

By crossing plants of different color genotypes, we can forecast potential offspring colors using these principles. This predictable nature of plant color inheritance showcases the fascinating interplay of genetics.

Mendelian Genetics

Mendelian genetics refers to the set of principles established by Gregor Mendel through his work on pea plants, formulating the foundational concepts of heredity. These principles apply to Collinsia parviflora, illustrating how characteristics such as petal color are passed from one generation to the next through predictable patterns.

Mendel's laws of inheritance include the Law of Segregation and the Law of Independent Assortment. The Law of Segregation explains how two alleles for a trait separate during gamete formation, ensuring each gamete carries only one allele for each trait. Meanwhile, the Law of Independent Assortment indicates that genes for separate traits are passed independently of one another. However, within Collinsia parviflora's petal color, we see an extension through multiple alleles affecting the phenotype.

Exploring the inheritance patterns through these lenses allows geneticists to predict outcomes of genetic crosses accurately. Mendel's principles remain crucial for analyzing the proportions of offspring phenotypes, enabling thoughtful interpretation of complex genetic interactions and facilitating advanced breeding strategies.