Mendelian inheritance is a kind of biological inheritance that follows the theories first put forth by Gregor Mendel in 1865 and 1866, which were later rediscovered in 1900 by Hugo de Vries and Carl Correns and popularised by William Bateson.
Mendel conducted a series of systematic experiments that examined 7 unique characteristics (for example, flower color, seed color, and seed shape) each with two distinct traits (e.g. white and purple flowers). For each trait, he produced true-breeding lines. For instance, a line of plants might only produce white flowers, whereas another might only produce purple flowers. He was curious about specific conditions. Therefore, he performed another cross between two plants with distinct characteristics to observe the offspring's final trait across three generations. He proposed three laws according to his observations and the Law of Segregation is one such rule used in studying the Mendelian inheritance of different colored and sized seeds of any plant.
To study Mendelian Inheritance using seeds of different colors and sizes of any plant.
Samples of Pea seeds or any other plant
Petri Dishes
Tray
Napkin
Pen/Pencil
Notebook.
The Law of Segregation is the basis for studying the Mendelian Inheritance using different colors and sizes of any plant. This law is based on one of the benchmark scientific experiments in genetics, the Mendel Pea Plant Experiment. Mendel chose the pea plant for this experiment for its measurable characteristics, short life cycle, and feasibility in breeding. Therefore, it became easy for Mendel to collect the data and conduct the experiment.
The points discussed below are the required steps in the procedure for the aforementioned experiment −
Collect 100-128 Pea seeds of different shapes, sizes, and colors.
Place these seeds in an enamel tray.
Sort out 64 round seeds and 64 wrinkled seeds in different Petri plates. Similarly, 64 green seeds and 64 yellow seeds can also be separated to study Mendelian inheritance.
The F1 progeny are represented by one yellow and one green seed.
Take one yellow and one green seed in a petri dish together until all the seeds from the previous two dishes are finished. As a result, 64 pairs of seeds will be formed in the F1 generation.
Now, put 32 progenies (pair of yellow and green seeds) in one petri dish and the remaining 32 in another petri dish representing the F1 males and females.
Mix both the Petri dishes well with the help of a pen or pencil so as to achieve a random pairing of the seeds.
Keep three Petri dishes ready to place seeds for the F2 generation as there could be three possibilities of the gene in the F2 generation. Let us consider YY for the yellow seeds, yy for green seeds, and Yy for the heterozygous dominant yellow seeds.
Mark each Petri dish according to the expected seed genotype.
Ask your friends or anybody to randomly pick two seeds from the Petri plates with F1 progeny and sort them out.
If two yellow seeds are being picked, then put them in the petri dish marked for YY genotype.
When two green seeds are picked, put them in the petri dish marked for yy genotype.
In the condition that when one yellow and one green seed are picked together, place them in the petri dish marked for Yy genotype.
The abovementioned step helps in finding out the genotype of the seeds in the F2 generation.
Now, observe the number of seeds carefully and note down their ratio.
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Make a table that includes the characteristics of seeds, the total number of observations, the number of seeds with contrasting traits, and the ratio.
| Characteristics | Total Number of Seeds | Genotype (F2 Gen)[YY: Yy: yy] | Ratio of phenotypes (F2 Gen) |
|---|---|---|---|
| Seed color | 128 | 32:64:32 Or 1:2:1 |
3:1 |
According to the observations following results can be concluded −
Yellow seed color is dominant over green color.
In the heterozygous condition, the green color of the seed was not expressed in the presence of the yellow color gene which indicates green color as the recessive character.
A gene can have more than one form or allele.
For each trait, an organism inherits two alleles.
Allele pairs split apart during the production of sex cells (during meiosis), leaving each cell with just one allele for each trait.
When two alleles in a pair differ, one is considered dominant and the other is recessive.
The Mendel Pea Experiment was an extremely innovative scientific study. The foundation of genetic science is laid by the Law of Segregation. The Mendel Pea Experiment was the first to investigate the mechanisms underlying heritable features, although other processes are also at play.
To study Mendelian Inheritance, students can use pea seeds of different colours, sizes, or shapes and execute an experiment following all the required steps.
Q1. What are Mendelian patterns of inheritance?
Ans. Understanding patterns of disease transmission requires knowledge of the fundamental principles of inheritance. Mendelian inheritance patterns are frequently used to describe single-gene disease inheritance patterns. There are generally five main inheritance patterns that can occur for single-gene disorders: autosomal recessive, autosomal dominant, X-linked recessive, X-linked dominant, and mitochondrial
Q2. What is Mendelism?
Ans. Mendelism is the term used to describe the single-gene trait theory of inheritance, which was formed from the idea put forth by Gregor Mendel regarding the transmission of hereditary features from parent organisms to their offspring. Mendel established the foundation for genetics during a time when meiosis was not fully understood, long before chromosomes or genes had been discovered. Mendel embarked on a decade-long investigation into the inheritance patterns of bees and plants, and he ultimately chose pea plants as his main model system.
Q3. How many observable traits did Mendel use for his experiment?
Ans. Mendel conducted studies using seven characteristics of the pea plant, including flower colour (purple or white), flower position (axil or terminal), seed shape (round or wrinkled), seed colour (yellow or green), stem length (long or short), pod colour (yellow or green) pod shape (inflated or constricted).
Q4. What are the exceptions to Mendel’s Laws?
Ans. Following are some of the most common exceptions to Mendel’s Laws −
The law of dominance is not observed if one of the alleles is unable to entirely disguise the influence of another allele. Codominance and incomplete domination are exceptions to this rule.
Chromosome non-disjunction, which results in aneuploidy, invalidates the Law of Segregation.
When two genes are linked together, which is feasible when they reside on the same chromosome, the Law of Independent Assortment is violated.
His theory that a character is influenced by a single "factor" does not hold true in a number of situations, such as polygenic inheritance, multiple allelism, etc.
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