Question

A hypothetical flowering plant species produces blue, light blue, and white flowers. To determine the inheritance pattern, the following crosses were conducted with the results indicated: blue \(\times\) blue \(\rightarrow\) all blue white \(\times\) white \(\rightarrow\) all white blue \(\times\) white \(\rightarrow\) all light blue What type of inheritance pattern does this represent? a. simple Mendelian b. X-linked c. codominance d. incomplete dominance e. pleiotropy

Short answer

The inheritance pattern represented in the experiment is incomplete dominance.

Step-by-step solution

Understand the results

First, take a look at the experiment's results. It's mentioned that when blue flowers are crossed with blue, the result is all blue. White with white gives all white. And blue with white gives all light blue.

Understand the inheritance patterns

Next, understand the definition of each of the inheritance patterns.\n\na) Simple Mendelian: An inheritance pattern that arises from a single gene that is found in two different forms, one of which is dominant over the other.\n\nb) X-linked: An inheritance pattern where a gene causing a trait or disorder is located on the X chromosome.\n\n c) Codominance: A pattern of inheritance in which both alleles for a gene are fully expressed\n\n d) Incomplete dominance: A pattern of inheritance where the phenotype of a heterozygote is intermediate between the phenotypes of the two homozygotes\n\n e) Pleiotropy: A pattern of inheritance where one gene impacts two or more unrelated phenotypic traits.

Compare results with patterns

Compare the results of the experiment with each inheritance pattern. The blue and white flowers when crossed produce light blue flowers, which suggests a blending of traits. Thus, the inheritance pattern here is not simple Mendelian (which usually gives distinct traits) nor is it X-linked (which is usually related to sex traits) nor codominance (both traits would be seen distinctly, not a blend) nor pleiotropy (multiple traits affected). The correct pattern as per the results is incomplete dominance (where an intermediate trait is produced).

Key concepts

Incomplete Dominance

In genetics, the term 'incomplete dominance' refers to a pattern of inheritance that is quite different from the traits Gregor Mendel observed in his pea plants. This pattern is particularly interesting because it results in offspring that do not resemble either parent with respect to a given trait but instead display a blend of parental characteristics. For instance, when we involve the hypothetical flowering plant species that produce blue, light blue, and white flowers—as per the exercise—the cross between blue and white flowers yielding all light blue offspring exemplifies this pattern. Unlike complete dominance where the dominant allele can overshadow the presence of a recessive one, incomplete dominance leads to a situation where both alleles in the heterozygote have a say in the final appearance of the organism.

When charting out a Punnett square, the 'middle' phenotype manifesting from a cross between two 'pure' phenotypes would typically be represented by a 1:2:1 ratio in the progeny (1 being the homozygous dominant, 2 the heterozygous, and 1 the homozygous recessive). Understanding incomplete dominance is integral for students as it better represents the complex nature of inheritance in real-world scenarios. Many traits in a diverse array of organisms, including humans, illustrate this non-Mendelian pattern of heredity. Falling back on the provided exercise, we can confidently assert that the offspring of the blue and white flower parents display incomplete dominance through the resulting light blue flowers.

Mendelian Inheritance

Mendelian inheritance is foundational to the field of genetics and pertains to the transmission of hereditary characteristics from parents to offspring. This concept was pioneered by Gregor Mendel, who in the 1860s conducted experiments on pea plants and uncovered that traits are inherited discretely through units now known as genes. The principles outlined by Mendel, comprising the Law of Segregation and the Law of Independent Assortment, form the core of classical genetics.

In simple Mendelian inheritance, traits are controlled by a single gene with two alleles, and one allele may be dominant over the other. Here lies the importance of distinguishing between homozygous genotypes, where both alleles are the same (either dominant or recessive), and heterozygous genotypes, where two different alleles are present. The exercise involving flower colors initially led us to question whether we were observing simple Mendelian inheritance. However, the absence of either purely blue or purely white flowers in the progeny of a blue and white cross negates this, thus proving it isn’t a case of simple dominance. This discrepancy between observed and expected results is a crucial learning point for students, demonstrating that genetic inheritance can be more nuanced than the Mendelian model suggests.

Genetics in Flowering Plants

Broadening our view beyond the initial Mendelian concepts, genetics in flowering plants can present relatively diverse and intricate patterns of inheritance. Flowering plants, known as angiosperms, serve as an excellent model for studying genetics due to the myriad of variations they exhibit in characteristics such as flower color, shape, size, and other phenotypes. This diversity can be attributed to the intricate systems of genetic control within these organisms, which include not only Mendelian genetics but also more complex modes of inheritance like incomplete dominance, as observed in the exercise with hypothetical flowering plants.

Studying the genetics of flowering plants involves looking into gene interactions, allelic relationships, and environmental influences on gene expression. This complexity is often revealed through dihybrid crosses or other more extensive breeding experiments. In studying these patterns, scholars can grasp the concepts of dominance, codominance, polygenic inheritance, and epistasis, to name a few. Flowering plants are perfect for these studies because they are easier to manipulate genetically and have shorter reproductive cycles. The insight gained from plant genetics can be monumental, contributing to fields like agriculture, where breeders endeavor to create plants with desirable traits such as improved resistance to diseases, pests, or environmental stresses.