Study on tandem repeat sequence variation in sheep mtDNA D-loop region

Area of Science:

• Animal Genetics
• Population Genetics
• Mitochondrial DNA Analysis

Background:

• Mitochondrial DNA (mtDNA) control region sequences, specifically tandem repeats, are crucial for understanding animal population genetics.
• Investigating genetic diversity and relationships within indigenous sheep breeds is essential for conservation and breeding programs.

Purpose of the Study:

• To investigate the origin and differentiation of Chinese indigenous sheep breeds.
• To analyze genetic diversity and relationships among these breeds using mtDNA control region sequences.

Main Methods:

• Sequencing of the 75-nt-long tandem repeat sequence in the mtDNA control region of 77 sheep individuals (69 indigenous Chinese, 8 imported).
• Analysis of 309 repeated sequences to detect variable sites and characterize genetic variation.
• Haplotype analysis to identify genetic diversity and relationships among sheep breeds.

Main Results:

• A total of 28 polymorphic sites were identified within the sequenced regions, leading to the sorting of 63 unique haplotypes.
• Two major haplotypes (Hap 1 and Hap 3) were found at high frequencies (12.94% and 30.42%, respectively).
• Altay and Kazakstan sheep showed close genetic relationships, as did Mongolian and Ujumuqin sheep. Tibetan, Mongolian, and Ujumuqin sheep exhibited lower genetic diversity compared to Altay and Kazakstan sheep.

Conclusions:

• Chinese indigenous sheep breeds likely originated from two distinct maternal ancestors, inferred from mtDNA analysis.
• Significant genetic differentiation was not observed between Altay and Kazakstan sheep breeds.
• Tibetan, Mongolian, and Ujumuqin sheep possess lower genetic diversity, highlighting potential conservation needs.