Mendel started his experiments in 1854, where he used pea plants to study heredity. He used pea plants for two main reasons. First, he started out by recording various traits, and noticing that these traits either had one type or another. In total, he observed 7 different traits. Second, pea plants generally self-fertilize, which means that the plants can reproduce with itself. This makes it easy to identify if plants are purebreds, and makes it easier to predict traits.

Once he noted these traits, he crossed two different purebreeding plants together to observe the traits of the offspring. His experimental design was that he would trim the anthers of the plant that was producing the seed to prevent it from self-fertilizing. Then, he would use a paintbrush to transfer pollen from the other purebreeding plant to control the cross. Afterwards, he would wrap the plant with the trimmed anthers in order to prevent any cross contamination. Mendel would then grow the offspring and observe their traits. This experimental designed was used for all of his experiments.

 

 

 

 

 

 

 

 

 

 

 

 

 

He crossed pollen from a plant that produced round seeds with eggs that produced wrinkled seeds. Now, the current thought for the inheritance of the offspring would be that they would have slightly wrinkled seeds. But, when he noticed the offspring, he saw that all of the offspring produced round seeds, which he called the F1 generation. He decided to switch the roles of the parents, and he noticed that he got the same result. He then repeated this experiment with the other traits that he noted, and he got similar results. This led Mendel to believe that traits did not blend, but instead some traits are expressed with others are not. He also stated that certain ‘factors’ control which traits are expressed. We now call these ‘factors’ genes, but when Mendel was completing his experiments, genes were not yet determined. Variations of a gene are known as alleles. The allele that was always expressed as the dominant allele, and the allele that was expressed when there was no dominant allele to be the recessive trait. Therefore, for this experiment the gene is seed shape, with round being the dominant allele, and wrinkled being the recessive allele.

Mendel went on to then cross two F1 generation offspring to observe what traits would be observed in their offspring, known as the F2 generation. The result was that some of the offspring produced round seeds and some also produced wrinkled seeds, but not evenly. This means that some offspring were expressing either the dominant trait or the recessive trait. There was also a specific ratio observed as well; a 3:1 ratio between round seeds and wrinkled seeds. This ratio is explained by the way that gametes are formed between the F1 and F2 generation. When meiosis occurs, the different alleles of a gene separate during gamete formation, and recombine with the other gamete that they fertilize with. This is known as the law of segregation.

Genotype refers to the set of alleles that an organism has for a particular trait. Phenotype refers to the observable traits of an individual. When the set of alleles for a gene are the same, the genotype is described as homozygous. When the set of alleles for a gene are different, the genotype is described as heterozygous. Therefore, if the phenotype of an organism reflects the dominant allele, the genotype can either be homozygous for the dominant trait, or heterozygous, as the dominant allele will get expressed over the recessive trait. If the phenotype of an organism reflects the recessive trait, that means that the genotype is homozygous recessive.