Assume specific language impairment (SLI) can be caused by a dominant allele. What is the probability that an individual who has SLI and an individual without it will have a child with SLI?

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Quizplus · Accepted Answer

If SLI is caused by a dominant allele, then the affected individual must be heterozygous for the allele (since if it were homozygous dominant, all offspring would have SLI and if it were homozygous recessive, it would not have SLI). Therefore, the affected individual must have one allele for SLI and one allele for normal language ability. The unaffected individual must have two alleles for normal language ability. When these two individuals have offspring, each will contribute one allele to the child. Therefore, the probability of the child inheriting the dominant SLI allele from the affected parent is 1/2, and the probability of inheriting an allele for normal language ability from the unaffected parent is 1. Multiplying these probabilities together gives 1/2, or a 50% chance that the child will inherit the SLI allele and have SLI.

Assume Specific Language Impairment (SLI) Can Be Caused by a Dominant