37. Identification of genes that are associated with the development of male and/or female gametophyte and embryogenesis in plants is facilitated by T-DNA mediated insertional mutagenesis.
    In an experiment, a transgenic plant was generated by insertion of T-DNA (containing a Kanamycin-resistance gene) into a gene “A”. Self-pollination of the T_o plant generated F₁ progeny that segregated in a 2 : 1 ratio for resistance : sensitivity to Kanamycin. These
    observations indicate that
    (1) the mutant allele did not segregate from the wild type allele.
    (2) mutation in gene “A” induces lethality in the male gametophyte.
    (3) mutation in gene “A” induces lethality in the female gametophyte.
    (4) mutation in gene “A” induces zygotic lethality.

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Introduction

T-DNA-mediated insertional mutagenesis is a powerful tool used to disrupt genes and study their functions in plants like Arabidopsis thaliana. Analysis of segregation ratios in progeny following self-pollination reveals the genetic consequences of mutations such as gametophytic or zygotic lethality, critical for understanding gene roles in plant reproduction and development.

Interpreting Segregation Ratios in T-DNA Mutants

• A typical Mendelian 3:1 ratio for a dominant marker reflects viability of all genotypes.

• A 2:1 ratio in the F1 progeny suggests homozygous mutant lethality; homozygous individuals fail to develop or die early in development, thus are not recovered.

• Male or female gametophytic lethal mutations show reduced transmission but usually do not produce exact 2:1 ratios and manifest as skewed segregation due to gamete dysfunction.

Implications of Zygotic Lethality

• Identification of zygotic lethal mutants helps pinpoint genes essential for embryo viability or early development.

• These mutants enable detailed analysis of gene function during embryogenesis and reproductive development.

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Summary Table: Segregation Ratios and Genetic Interpretations

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Conclusion

A 2:1 segregation ratio for Kanamycin resistance following T-DNA insertion in Arabidopsis suggests zygotic lethality from mutation in gene “A,” eliminating homozygous mutant progeny.