8. A cross is made between two plants with white flowers. All the F1 progeny had red coloured flower. This is because of
(1) complementation    (2) recombination
(3) translocation          (4) reversion

The correct answer to why all F1 progeny had red flowers when two white-flowered plants were crossed is (1) complementation.

Explanation of Each Option

• (1) Complementation: This occurs when two parents with white flowers each have mutations in different genes required for red pigment production. When crossed, the F1 offspring inherit one functional copy of each gene from both parents, restoring the pathway for red pigment synthesis, resulting in red flowers. This explains why two white-flowered plants can produce red-flowered progeny.

• (2) Recombination: This involves exchange of genetic material between chromosomes. While important for genetic variation, recombination does not directly explain how two white-flowered parents produce red-flowered offspring.

• (3) Translocation: This is a chromosomal abnormality where segments of chromosomes are rearranged. It is unrelated to the production of a specific flower color phenotype in such crosses.

• (4) Reversion: This is a mutation that reverses a previous mutation, restoring the original phenotype. It does not typically explain all progeny showing a new phenotype from two white parents.

Introduction

In genetics, it may seem surprising when crossing two white-flowered plants results in all F1 progeny having red flowers. This phenomenon is explained by complementation, where mutations in different genes of the pigment synthesis pathway in each parent complement each other to restore red flower color in the offspring.

Understanding Complementation in Flower Color

Complementation occurs when two parents have mutations in different genes essential for a trait, such as flower color. Neither parent can produce pigment alone due to missing functional alleles. However, their offspring inherit functional alleles from each parent, complementing each other’s deficiencies. Thus, the pigment pathway is restored, and red flowers appear.

Why Other Genetic Mechanisms Don’t Apply

• Recombination involves gene shuffling, not restoration of lost functions.

• Translocation affects chromosome structure but doesn’t explain phenotypic complementation.

• Reversion is a rare mutation reversing an earlier mutation, not responsible for F1 phenotype changes in this context.

This explanation of complementation provides insight into complex genetic interactions, crucial for understanding inheritance patterns beyond simple dominance and recessiveness.