Twinning and mitotic crossing-over: some possibilities and their implications

Area of Science:

• Genetics
• Developmental Biology
• Human Physiology

Background:

• Mitotic crossing-over, a genetic recombination process, is recognized but its frequency and significance in humans are underestimated.
• Its occurrence post-fertilization, particularly before monozygotic (MZ) twin differentiation, has theoretical implications for genomic regulation and embryonic development.
• Existing data on MZ twin discordance and certain genetic disorders suggest a need for revised models of human development and inheritance.

Purpose of the Study:

• To investigate the frequency and impact of mitotic crossing-over in human development.
• To explore the role of mitotic crossing-over in monozygotic (MZ) twin discordance and developmental abnormalities.
• To propose a new model linking mitotic crossing-over to twinning and the genetic mapping of complex diseases.

Main Methods:

• Theoretical modeling based on existing data of mitotic crossing-over and MZ twin discordance.
• Review and re-evaluation of literature concerning genetic diseases, twinning, and developmental malformations.
• Hypothesis generation regarding sex differences in mitotic crossing-over rates and X chromosome inactivation.

Main Results:

• Mitotic crossing-over is more frequent and significant in humans than previously thought.
• Postzygotic mitotic crossing-over can disrupt genomic imprinting and cis-acting sequences, leading to lethality or MZ twin discordance.
• Hypothesized sex differences in mitotic crossing-over rates and implications for X chromosome inactivation.

Conclusions:

• Mitotic crossing-over plays a crucial role in human development, potentially inducing twinning and midline malformations.
• The proposed model offers a novel approach for gene mapping of multifactorial and irregularly inherited disorders.
• Further molecular testing is recommended to validate the proposed mechanisms and their clinical relevance.