(a) Why is the F1 Progeny Always of Tall Plants When a Tall Pea Plant Is Crossed with A Short Pea Plant? (b) How Is F2 Progeny Obtained by Self-Pollination of F1 Progeny Different from F1 Progeny? Give Reason for This Observation. (c) State A Conclusion That Can Be Drawn On the Basis of This Observation.


Introduction

The study of genetics has been one of the most intriguing and thought-provoking fields in biology. Since the discovery of DNA, scientists have been trying to unravel the secrets of heredity and understand how traits are passed on from one generation to the next. One of the most famous experiments in genetics is the cross between tall and short pea plants by Gregor Mendel, which led to the discovery of the laws of inheritance.

Part 1: Why is the F1 Progeny Always Tall When a Tall Pea Plant Is Crossed with A Short Pea Plant?

Gregor Mendel conducted his experiments on pea plants and observed the inheritance of seven different traits. One of these traits was plant height. He crossed tall pea plants with short pea plants and observed that the resulting F1 progeny were always tall.

This result was surprising because the parents had different heights, and it was expected that the F1 progeny would be intermediate in height. However, this was not the case. The F1 progeny were always tall.

The reason for this observation lies in the genetic makeup of the plants. Each plant has two copies of each gene, one from the father and one from the mother. These copies are called alleles. The alleles can be either dominant or recessive. The dominant allele is expressed even if only one copy is present, while the recessive allele is only expressed if both copies are present.

In the case of plant height, the tall allele is dominant, while the short allele is recessive. This means that if a plant has one copy of the tall allele and one copy of the short allele, it will be tall because the tall allele is expressed. This is what happens in the F1 progeny of the cross between tall and short pea plants. The tall allele from the tall parent is dominant over the short allele from the short parent, and so the F1 progeny are tall.

Part 2: How is F2 Progeny Obtained by Self-Pollination of F1 Progeny Different from F1 Progeny? Give Reasons for This Observation

To understand the differences between F1 and F2 progeny, we need to understand how Mendel obtained his F1 progeny. He crossed a purebred tall pea plant with a purebred short pea plant. A purebred plant has two identical copies of a gene, one from the father and one from the mother. In this case, the tall parent had two copies of the tall allele, while the short parent had two copies of the short allele.

When these two plants were crossed, the resulting F1 progeny had one copy of the tall allele and one copy of the short allele. As we have already discussed, the tall allele is dominant over the short allele, and so the F1 progeny were always tall. However, when the F1 progeny were self-pollinated, the resulting F2 progeny showed some interesting results.

The F2 progeny were a mixture of tall and short plants in a ratio of 3:1. This was unexpected because it was thought that the F1 progeny would be intermediate in height. However, this was not the case. The reason for this can be explained by the laws of segregation and independent assortment.

The law of segregation states that the two alleles of a gene segregate from each other during the formation of gametes. This means that each gamete contains only one copy of each gene. In the case of plant height, this means that each gamete from the F1 plants will contain either the tall or the short allele, but not both.

The law of independent assortment states that the alleles of different genes segregate independently of each other during the formation of gametes. This means that the inheritance of one trait does not affect the inheritance of another trait. In the case of plant height, this means that the inheritance of the tall or short allele for plant height does not affect the inheritance of other traits.

When the F1 plants self-pollinate, the tall and short alleles segregate from each other according to the law of segregation. This means that some of the gametes will contain the tall allele, while others will contain the short allele. When these gametes fuse during fertilization, the resulting F2 plants will have different combinations of alleles for plant height.

There are three possible genotypes for the F2 plants: TT (homozygous tall), Tt (heterozygous tall), and tt (homozygous short). The ratio of these genotypes is 1:2:1, which corresponds to the ratio of tall to short plants in the F2 generation.

Part 3: State A Conclusion That Can Be Drawn On the Basis of This Observation

The observation that the F1 progeny are always tall when a tall pea plant is crossed with a short pea plant, and that the F2 progeny obtained by self-pollination of F1 progeny are a mixture of tall and short plants in a ratio of 3:1, can lead to several conclusions.

Firstly, it shows that plant height is a trait that is controlled by a single gene with two alleles. The tall allele is dominant over the short allele, which means that it is always expressed when present.

Secondly, it shows that the inheritance of traits is governed by the laws of segregation and independent assortment. These laws explain why the F1 progeny are always tall and why the F2 progeny are a mixture of tall and short plants.

Finally, it shows that the genotype of an individual determines its phenotype. The genotype is the genetic makeup of an individual, while the phenotype is the observable physical or biochemical characteristic. In the case of plant height, the genotype determines whether an individual is tall or short.

Conclusion

In conclusion, the study of genetics has led to many important discoveries, including the laws of inheritance and the principles of segregation and independent assortment. The cross between tall and short pea plants by Gregor Mendel led to the discovery of the laws of inheritance, and showed that plant height is a trait controlled by a single gene with two alleles.

The F1 progeny of this cross are always tall because the tall allele is dominant over the short allele, while the F2 progeny obtained by self-pollination of F1 progeny are a mixture of tall and short plants in a ratio of 3:1, due to the laws of segregation and independent assortment. This observation has led to many important conclusions about the inheritance of traits, and has paved the way for further research in the field of genetics.

Updated on: 03-May-2023

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