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Individuals who are first cousins and are planning to have children (or are expecting a child) may wish to pursue a consultation with a genetic counselor to explore the possibility of their child(ren) inheriting a genetic disorder that is rare in the general population, but may be more likely in their offspring due to their genetic relatedness.

Anytime that mating occurs between relatives there is increased homozygosity among the resulting progeny as compared to progeny from unrelated parents. The paths of relationship are more easily seen with an arrow diagram as compared to other pedigree or family tree presentations.

Relationship between individuals is based on the number of steps in each path as well as the number of paths that connect the individuals, and this type of relationship is referred to as the additive genetic covariance.

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The inbreeding coefficient of an individual is one half of the additive genetic covariance of its parents.

Based on the arrow diagram, determine (i) the additive genetic covariance between Cousin 1 and Cousin 2 and (ii) the inbreeding coefficient of any potential progeny resulting from the marriage of Cousin 1 and Cousin 2.


50%, 25%


25%, 12.5%


12.5%, 6.25%


6.25%, 3.125%

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