A Scientist Crossed True-breeding Tall and Hairy-stemmed Tomato Plants

Genetics has always been a fascinating field for scientists, and there have been several experiments proving the theories of inheritance postulated by Gregor Mendel. One such experiment involved crossing true-breeding tall and hairy-stemmed tomato plants. The results of this experiment provided valuable insights into the patterns of inheritance.

Mendelian Genetics

Gregor Mendel, an Austrian monk, conducted experiments with pea plants in the mid-1800s and discovered the laws of inheritance. Mendelian genetics postulates that traits are inherited from parents in a predictable manner. Factors (genes) that determine traits are inherited in pairs, and there are dominant and recessive alleles for each trait. The offspring inherit one allele from each parent, and the dominant allele determines the trait expressed in the offspring.

The Experiment

The scientist crossed true-breeding tall and hairy-stemmed tomato plants. True-breeding plants are those that produce offspring with the same traits generation after generation. The tall and hairy-stemmed traits are controlled by different genes, and each trait has a dominant and recessive allele. In this case, the tall stem is dominant over the short stem, and the hairy stem is dominant over the smooth stem.

The results of the experiment showed that all the F1 (first filial) offspring had tall stems and hairy stems. This was expected since the dominant traits were expressed in the offspring. However, when the F1 offspring bred with each other, the F2 (second filial) offspring showed a 3:1 ratio of tall to short stems and a 2:1 ratio of hairy to smooth stems. This was unexpected as it suggested that the traits were segregating independently.

The Explanation

The observed 3:1 ratio of tall to short stems in the F2 offspring can be explained by the fact that the tall stem trait is controlled by a single gene. Each parent contributes one allele, and the offspring inherit one tall allele and one short allele. Since the tall allele is dominant, the offspring will have a tall stem if they inherit at least one tall allele.

Similarly, the 2:1 ratio of hairy to smooth stems in the F2 offspring can be explained by the presence of two genes controlling this trait. Each parent contributes one allele for each gene, and the offspring inherit one hairy allele and one smooth allele for each gene. The ratios observed can be explained using a Punnett square.

The Significance

This experiment provided valuable insights into the patterns of inheritance and the behavior of genes. It showed that traits are inherited in a predictable manner, but the expression of these traits can be influenced by multiple genes. It also demonstrated the concept of segregation of alleles, where the different alleles for a gene separate during gamete formation and randomly combine during fertilization. This experiment paved the way for further studies on inheritance and genetics, which have led to many breakthroughs in the field of biology.

In conclusion, the experiment of crossing true-breeding tall and hairy-stemmed tomato plants provided important insights into inheritance patterns and behavior of genes. It highlighted the concept of segregation of alleles and the presence of multiple genes controlling a single trait. Overall, this experiment was groundbreaking in the field of genetics and provided the foundation for further studies on inheritance and genetics.