Pseudoautosomal region 1 length polymorphism in the human population.

Area of Science:

• Genetics
• Evolutionary Biology
• Genomics

Background:

• Human sex chromosomes (X and Y) share homologous pseudoautosomal regions (PAR1 and PAR2) at their termini.
• The boundaries between PARs and unique sex chromosome sequences evolved during primate divergence.
• Copy number variation screening identified paternally inherited X chromosome duplications.

Purpose of the Study:

• To investigate the genomic basis of a paternally inherited X chromosome duplication.
• To understand the mechanism generating an extended pseudoautosomal region (PAR).
• To determine the evolutionary significance of this recurrent genomic rearrangement.

Main Methods:

• Genomic analysis of affected families.
• Identification of non-allelic homologous recombination events.
• Analysis of repeat sequences (LTR6B) involved in the rearrangement.
• Haplogroup analysis of Y chromosomes.

Main Results:

• An insertional translocation of X chromosomal sequence into the Y chromosome was identified.
• This rearrangement extends the PAR1 region.
• The insertion is mediated by non-allelic homologous recombination between LTR6B repeats.
• A reciprocal deletion on the X chromosome was observed in one family.
• The variant occurs across different Y chromosome haplogroups, indicating recurrence.

Conclusions:

• A novel mechanism involving insertional translocation and homologous recombination shapes human sex chromosome evolution.
• This recurrent genomic rearrangement extends the pseudoautosomal region (PAR).
• The findings provide new insights into the dynamic nature of the human genome and sex chromosome evolution.