When Mendel uncovered his findings, there was no prevailing theory to explain how characteristics are passed down from parents to offspring. This gap in knowledge drove Mendel to explore the fundamental concepts of heredity.
He began with pea plants, which naturally self-fertilize when pollinated with another species’ flowers. This allows him to selectively breed pea plants so that their offspring would look just like their parents.
The blending theory
The blending theory of inheritance is the idea that organisms pass traits from parents to offspring without complete dominance. This concept is also known as non-Mendelian inheritance.
In 1857, Gregor Mendel first proposed the blending theory when he conducted experiments with purebred pea plants. As a monk in an Augustinian order, his research focused on how genes could shape physical characteristics like flower color.
Mendel was intrigued by his garden’s diversity of plants that didn’t share the same characteristics as their parents. He wondered if there was any explanation behind these differences and used purebred pea plants as a laboratory to explore genetics and learn what he could about heredity at that time.
Mendel’s initial experiments focused on the genetic composition of pea seeds through cross-pollination. He crossed true-breeding plants with green or yellow seeds and then tested the results from each generation.
He observed that the F1 generation consisted of half the genes from each parent plant. He then crossed these plants together, producing the F2 generation of hybrids.
Mendel carefully chose unlinked genes so as to not be caught off guard by linkage, which occurs when two genes merge. Otherwise, he would have had difficulty deciphering his results and creating a mathematical model of them based on what he observed.
Contrary to a commonly held misconception in the scientific community, Mendel did not need to worry about homologous recombination when his crosses were between genes located far apart on different chromosomes.
Mendel’s research demonstrated that traits like flower color, height and texture are transmitted through particulate matter in plants’ bodies. He named these parts “factors,” and explained why these particles caused the traits he observed in his experiments. Through his work Mendel contributed to developing modern theories of heredity – being widely credited as the Father of Genetics.
The law of independent assortment
Gregor Mendel discovered the law of independent assortment, one of the laws of inheritance through his experiments with pea plants. This law explains how certain traits are inherited in relation to others and also provides insight into how genetic information is passed from generation to generation.
Mendel’s experiments with pea plants provided him with an insight into how units of heredity, or genes, function. When he crossed different pea plants with two distinct traits, all offspring (known as F1 or filial progeny) shared one trait.
He observed that plants with yellow, round peas were dominant over those with wrinkled green peas, leading him to believe all offspring would have these same characteristics due to their dominant round shape and color.
His research led him to develop the second law of inheritance, known as “The Law of Independent Assortment.” This principle states that distinct traits from different alleles are inherited independently by a zygote.
Independent assortment is a stage in meiosis that occurs in eukaryotes during metaphase I of meiotic division. During this time, chromosomes are mixed up and randomly sorted into gametes – an essential step for sexual reproduction as it produces a diploid zygote with all necessary DNA for formation into an organism.
Meiosis produces haploid gametes, or cells with half the number of chromosomes as a regular diploid cell does. Each chromosome in a diploid cell has 23 copies and two gametes are created for every copy present.
As meiosis progresses, recombination scrambles pieces of maternal and paternal genes to form new combinations that can be passed on to the zygote. This scrambling helps ensure independent assortment as the maternal and paternal chromosomes are divided.
The law of independent assortment is an essential step in inheritance, as it encourages genetic diversity and allows different combinations to be passed along. This diversity in genes has a major effect on evolution and how an organism develops over time.
Cross-pollination
Mendel conducted numerous experiments to investigate the inheritance of various pea features, such as height and flower color. He used purebred (offspring that always look identical to their parents) pea plants in order to perform multiple crosses.
Mendel discovered that pea plant height is determined by two heritable factors in distinct versions. He labeled one form the dominant trait and the other recessive trait, noting that these traits could be inherited independently of one another and studied separately through probability analyses.
Mendel conducted experiments by crossing pea plants with different traits, such as tall and short height, green seeds and yellow seeds, round seeds and wrinkled seeds. He then observed the offspring from these crosses and recorded their characteristics.
Mendel’s experiments revealed that one form of a trait always concealed the other in the first generation after crossing, making it easier for him to recognize inheritance patterns.
His experiments revealed that when he crossed tall and short pea plants together, the offspring had a 3:1 ratio of tall to short. He repeated this experiment using different traits such as green seeds versus yellow seeds, round versus wrinkled peas, etc.
Mendel also observed that when he crossed plants with different traits, the recessive trait would reappear in their offspring – proof of hereditary inheritance. From these observations he created two laws of inheritance: segregation and dominance – which govern how traits are passed down through generations.
The law of segregation dictates that paired unit factors (genes) must separate into gametes in such a way that offspring have an equal chance of inheriting either factor. When Mendel crossed plants with green, wrinkled seeds with another variety having yellow, round seeds, the offspring all carried the YYRR gene sequence.
Mendel performed this dihybrid cross by not removing the stamen from plants he wanted to use for his experiment. He did this to prevent self-pollination, which occurs when pollen grains containing male gametes (sex cells) from one plant fertilize the female gametes (sex cells) of another.
Mendel’s method
Pea plants make ideal candidates for experiments on inheritance due to their ease of cultivation, rapid growth rate and distinctive traits. Furthermore, pea plants can be controlled through self-pollination or cross-pollination.
Mendel’s method for conducting experiments involved cultivating a large number of purebred pea plants over several years and meticulously recording their characteristics. He then allowed these same plants to self-pollinate during that same timeframe, carefully observing the offspring that emerged.
He recorded the number of peas with each trait that were grown in each generation and used this data to identify which traits could be inherited independently from one another, thus creating the law of independent assortment and segregation (Wordsworth 2001).
Mendel’s initial experiment involved crossing two pure lines of pea plants with distinct traits, such as tallness or shortness. He observed that the F1 plants, or F2 plants, were tall and displayed all of the traits characteristic of tall plants (i.e., flower color, pod size and seed shape), unlike their shorter counterparts which displayed only some traits.
In a second experiment, Mendel crossed these F1 plants with pure-bred pea plants that shared similar traits but different combinations. He discovered that second generation hybrids had an even 3:1 ratio of dominant to recessive traits (i.e., yellow round seeds versus green wrinkled seeds).
Mendel’s findings from his initial experiment led him to formulate his second law of inheritance, which states that traits are inherited independently from each other. Furthermore, the 9:3:3:1 ratio he observed held regardless of which two traits were crossed, suggesting independent inheritance.
Mendel then set out to test a few more traits in order to better comprehend their role in inheritance. He selected seven contrasting traits such as purple or white flower color; flowers positioned atop of stem; smooth or pinched seed pod; yellow or green pod color; round or wrinkled seeds; long or short stems; and number of plants with each trait within each generation.
