Genetic relatedness refers to the degree of genetic similarity between individuals, based on the probability of sharing a focal gene. This concept is central to understanding various evolutionary phenomena, particularly those related to social behaviors.
Understanding Genetic Relatedness
Genetic relatedness essentially quantifies how much genetic material two individuals have in common due to shared ancestry. This shared ancestry leads to a higher likelihood of possessing identical genes. It's important to note that genetic relatedness is a probability, not a certainty.
The Role of Shared Genes
The probability of sharing a "focal gene" is the cornerstone of measuring genetic relatedness. A focal gene is simply a gene of particular interest in a given analysis.
Genetic Relatedness in Evolution
As our reference indicates, genetic relatedness plays a crucial role in evolution, especially concerning:
- Kin selection: The evolutionary strategy that favors the reproductive success of an organism's relatives, even at a cost to the organism's own survival and reproduction.
- Inclusive fitness theory: This theory suggests that an organism's fitness is based on its own reproductive success plus its contribution to the reproductive success of its relatives.
Why is Genetic Relatedness Important?
Understanding genetic relatedness helps explain behaviors that might otherwise seem paradoxical. For instance, altruism—where an individual acts in a way that benefits another at a cost to themselves—can be explained through the lens of kin selection. If the recipient of the altruistic act shares genes with the altruist, then helping that relative increases the chances of those shared genes being passed on, even if the altruist incurs a cost.
Calculating Genetic Relatedness: Examples
While the exact calculation can be complex, some common examples demonstrate the concept:
| Relationship | Coefficient of Relatedness (r) |
|---|---|
| Identical Twins | 1.0 |
| Parent-Offspring | 0.5 |
| Full Siblings | 0.5 |
| Half Siblings | 0.25 |
| Grandparent-Grandchild | 0.25 |
| First Cousins | 0.125 |
- Identical Twins (r = 1.0): They share 100% of their genes.
- Parent-Offspring (r = 0.5): On average, offspring inherit 50% of their genes from each parent.
- Full Siblings (r = 0.5): They share, on average, 50% of their genes by descent.
- First Cousins (r = 0.125): They share, on average, 12.5% of their genes by descent.
In Summary
Genetic relatedness provides a framework for understanding the evolutionary basis of social interactions and the spread of altruistic behaviors.
