1. What is Shared cM?

Shared centimorgans (cM) measure the length of DNA segments shared between two individuals. It's a key metric in genetic genealogy for estimating relationships between DNA matches.

2. How Does the Calculator Work?

The calculator uses the simple formula:

Where:

• \( \text{cM\_segments} \) — Array of shared DNA segments in centimorgans
• \( \sum \) — Summation of all segment values

Explanation: The calculator simply adds up all the cM values from the segments you provide to give the total shared cM.

3. Importance of Shared cM Calculation

Details: Total shared cM is crucial for determining possible relationships between DNA matches. Different relationship types typically fall within specific cM ranges.

4. Using the Calculator

Tips: Enter all shared segments as comma-separated values (e.g., "12.5, 8.2, 35.7"). The calculator will sum them to give the total shared cM.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical shared cM range for close relatives?
A: Parent/child share about 3400 cM, full siblings about 2600 cM, first cousins about 850 cM.

Q2: How accurate is shared cM for relationship prediction?
A: While useful, shared cM alone can't definitively determine relationships due to random recombination. Always consider genealogical context.

Q3: What's considered a significant shared cM amount?
A: Generally, segments over 7 cM are considered meaningful, though smaller segments may be valid especially in endogamous populations.

Q4: Why do some segments disappear at higher thresholds?
A: DNA companies often don't show smaller segments (typically under 5-7 cM) to reduce false positives from coincidental matches.

Q5: How does shared cM relate to percentage of DNA shared?
A: Approximately, 1% shared DNA ≈ 68 cM, though this varies by chromosome and specific segments.