How Austrian monk Gregor Mendel laid the foundations of genetics. Mendel's life, experiments, and pea plants.
How can we study inheritance?
When spending time with your own family, friends, and neighbors, you may have noticed that many traits run in families. For instance, members of a family may share similar facial features, hair color (like the brother and sister below), or a predisposition to health problems such as diabetes. Characteristics that run in families often have a genetic basis, meaning that they depend on genetic information a person inherits from his or her parents.
What if you wanted to figure out how genetic information is transmitted between generations? For instance, you might be curious how traits can "skip" a generation, or why one child in a family may suffer from a genetic disease while another does not. How could you go about asking these kinds of questions scientifically?
An obvious first idea would be to study human inheritance patterns directly, but that turns out to be a tricky proposition (see the pop-up below for details). In this article, we'll see how a nineteenth-century monk named Gregor Mendel instead uncovered the key principles of inheritance using a simple, familiar system: the pea plant.
[Why didn't Mendel study humans?]
The monk in the garden: Gregor Mendel
Johann Gregor Mendel (1822–1884), often called the “father of genetics,” was a teacher, lifelong learner, scientist, and man of faith. It would be fair to say that Mendel had a lot of grit: he persevered through difficult circ*mstances to make some of the most important discoveries in biology.
As a young man, Mendel had difficulty paying for his education due to his family's limited means, and he also suffered bouts of physical illness and depression; still, he persevered to graduate from high school and, later, university
His decision to join the order (against the wishes of his father, who expected him to carry on the family farm) appears to have been motivated in part by a desire to continue his education and pursue his scientific interests
Research on heredity
In 1856, Mendel began a decade-long research project to investigate patterns of inheritance. Although he began his research using mice, he later switched to honeybees and plants, ultimately settling on garden peas as his primary model system
Mendel studied the inheritance of seven different features in peas, including height, flower color, seed color, and seed shape. To do so, he first established pea lines with two different forms of a feature, such as tall vs. short height. He grew these lines for generations until they were pure-breeding (always produced offspring identical to the parent), then bred them to each other and observed how the traits were inherited.
In addition to recording how the plants in each generation looked, Mendel counted the exact number of plants that showed each trait. Strikingly, he found very similar patterns of inheritance for all seven features he studied:
One form of a feature, such as tall, always concealed the other form, such as short, in the first generation after the cross. Mendel called the visible form the dominant trait and the hidden form the recessive trait.
In the second generation, after plants were allowed to self-fertilize (pollinate themselves), the hidden form of the trait reappeared in a minority of the plants. Specifically, there were always about
plants that showed the dominant trait (e.g., tall) for every plant that showed the recessive trait (e.g., short), making a ratio.Mendel also found that the features were inherited independently: one feature, such as plant height, did not influence inheritance of other features, such as flower color or seed shape.
In 1865, Mendel presented the results of his experiments with nearly 30,000 pea plants to the local Natural History Society. Based on the patterns he observed, the counting data he collected, and a mathematical analysis of his results, Mendel proposed a model of inheritance in which:
Characteristics such as flower color, plant height, and seed shape were controlled by pairs of heritable factors that came in different versions.
One version of a factor (the dominant form) could mask the presence of another version (the recessive form).
The two paired factors separated during gamete production, such that each gamete (sperm or egg) randomly received just one factor.
The factors controlling different characteristics were inherited independently of one another.
We'll take a closer look at how Mendel reached these conclusions in the articles on the law of segregation and the law of independent assortment. In 1866, Mendel published his observations and his model of inheritance, under the title Experiments in Plant Hybridization
Scientific legacy
Mendel's work went largely unnoticed by the scientific community during his lifetime. How could this have been the case?
In part, Mendel's contemporaries failed to recognize the importance of his work because his findings went against prevailing (popular) ideas about inheritance. In addition, although we now see Mendel's mathematical approach to biology as innovative and pioneering, it was new, unfamiliar, and perhaps confusing or unintuitive to other biologists of the time
In the mid-1800s, when Mendel was doing his experiments, most biologists subscribed to the idea of blending inheritance. Blending inheritance wasn't a formal, scientific hypothesis, but rather, a general model in which inheritance involved the permanent blending of parents' characteristics in their offspring (producing offspring with an intermediate form of a characteristic)
But the blending model could not explain why Mendel crossed a tall and a short pea plant and got only tall plants, or why self-fertilization of one of those tall plants would produce a
As it turns out, both pea plant height and human height (along with many other characteristics in a wide range of organisms) are controlled by pairs of heritable factors that come in distinctive versions, just as Mendel proposed. In humans, however, there are many different factors (genes) that contribute fractionally to height and vary among individuals. This makes it difficult to see the contribution of any one factor and produces inheritance patterns that can resemble blending. In Mendel's experiments, in contrast, there was just one factor that differed between the tall and short pea plants, allowing Mendel to clearly see the underlying pattern of inheritance.
In 1868, Mendel became abbot of his monastery and largely set aside his scientific pursuits in favor of his pastoral duties. He was not recognized for his extraordinary scientific contributions during his lifetime. In fact, it was not until around 1900 that his work was rediscovered, reproduced, and revitalized. Its rediscoverers were biologists on the brink of discovering the chromosomal basis of heredity – that is, about to realize that Mendel's “heritable factors” were carried on chromosomes.
Mendel’s model system: The pea plant
Mendel carried out his key experiments using the garden pea, Pisum sativum, as a model system. Pea plants make a convenient system for studies of inheritance, and they are still studied by some geneticists today.
Useful features of peas include their rapid life cycle and the production of lots and lots of seeds. Pea plants also typically self-fertilize, meaning that the same plant makes both the sperm and the egg that come together in fertilization. Mendel took advantage of this property to produce true-breeding pea lines: he self-fertilized and selected peas for many generations until he got lines that consistently made offspring identical to the parent (e.g., always short).
Pea plants are also easy to cross, or mate in a controlled way. This is done by transferring pollen from the anthers (male parts) of a pea plant of one variety to the carpel (female part) of a mature pea plant of a different variety. To prevent the receiving plant from self-fertilizing, Mendel painstakingly removed all of the immature anthers from the plant’s flowers before the cross.
Because peas were so easy to work with and prolific in seed production, Mendel could perform many crosses and examine many individual plants, making sure that his results were consistent (not just a fluke) and accurate (based on many data points).
Mendel’s experimental setup
Once Mendel had established true-breeding pea lines with different traits for one or more features of interest (such as tall vs. short height), he began to investigate how the traits were inherited by carrying out a series of crosses.
First, he crossed one true-breeding parent to another. The plants used in this initial cross are called the
Mendel collected the seeds from the
Once Mendel examined the
Mendel's experiments extended beyond the
Mendel didn’t just record what his plants looked like in each generation (e.g., tall vs. short). Instead, he counted exactly how many plants with each trait were present. This may sound tedious, but by recording numbers and thinking mathematically, Mendel made discoveries that eluded famous scientists of his time (such as Charles Darwin, who carried out similar experiments but didn’t grasp the significance of his results)
You can use the links below to learn more about Mendel's laws of inheritance:
The law of segregation, describing how individual traits are inherited.
The law of independent assortment, describing how two or more traits are inherited relative to one another.
[Attribution and references]
what is difference between geneotype and phenotype • (24 votes) genotype = genetic code (78 votes) what does it mean when it says that it "self fertilizes"? • (20 votes) Self fertilizing is when the pollen from one plant is put on the stigma of the same flower or another flower that is growing on the same plant. (31 votes) What does F1 generation mean? It doesn`t make sense. • (2 votes) The F stands for filial, which comes from the Latin word filius, meaning son. F1 means the first generation of children (or baby pea plants). (50 votes) why the ratio is always roughly 3:1 not exactly? • (12 votes) It is correct that it won't be exactly half ,because as Alexander said, there would be slight imperfections (nothing is absolute ,I mean). (8 votes) What determines what gamete is chosen to move on? Or is it just random, and each gamete has an equal chance at being passed on to the offspring? • (12 votes) Does garden pea, Pisum sativum has a discontinue character on height, colour...? mostly those characters are continuous, they are controlled by many genes. (6 votes) why did he use pea plants, why not any other flower? • (4 votes) because pea was an annual plant and its was a self fertilizing plant and its easy to manually fertilize it (16 votes) How can we identify that after breeding multiple times we have got a hom*ozygotic offspring and does multiple breeding results in a hom*ozygote offspring ? • (8 votes) When 2 parents breed, they each have a genotype, let's say one is AA, the other is aa. Both are purebred and hom*ozygous. In its offspring, they create a new genotype, one letter from each of the parent's genotype. This creates many outcomes, including the heterozygous, Aa. (4 votes) If a tall plant and a short plant bred together, how would all of the plants end up being tall? Wouldn't 75% become tall and 25% become short based on the 3:1 ratio? • (3 votes) All plants would end up being tall if the parents are hom*ozygous for the traits controlling each character. 75% would be tall if and only if the p generation is heterozygous for the character while 25% would be short, which conforms to the 3:1 ratio. (9 votes) what is difference between geneotype and phenotype • (5 votes) Genotype is the specific gene alleles where as the phenotype is the physical expression of the alleles. (5 votes) what does allele mean? • (4 votes) An allele is a variant of a gene. I.e. dominant or recessive. E.g. A or a. (4 votes)Want to join the conversation?
phenotype = physical appearance/properties/expression of the gene
But , for this pea plant experiment ,I think it would be that tall and short are compound traits ,like they are made up from a combination of small traits.