Microsatellites are currently exploited as markers for paternity testing. A sample paternity test is shown in the following table in which ten microsatellite markers were used to test samples from a mother, her child, and an alleged father. The name of the microsatellite locus is given in the left-hand column, and the genotype of each individual is recorded as the number of repeats he or she carries at that locus. For example, at locus D9S302, the mother carries 30 repeats on one of her chromosomes and 31 on the other. In cases where an individual carries the same number of repeats on both chromosomes, only a single number is recorded. (Some of the numbers are followed by a decimal point, for example, 20.2, to indicate a partial repeat in addition to the complete repeats.) Assuming that these markers are inherited in a simple Mendelian fashion, can the alleged father be excluded as the source of the sperm that produced the child? Why or why not? Explain.

Key Concepts

Microsatellites

Microsatellites, or short tandem repeats (STRs), are repetitive sequences of DNA that vary in length among individuals. They are highly polymorphic, meaning they have many different alleles in a population, making them useful for genetic profiling. In paternity testing, the number of repeats at specific loci is compared between the mother, child, and alleged father to determine genetic relationships.

Mendelian Inheritance

Mendelian inheritance refers to the principles of genetic inheritance established by Gregor Mendel, which include the segregation and independent assortment of alleles. In the context of microsatellites, this means that a child inherits one allele from each parent at each locus. Understanding this concept is crucial for determining whether the alleged father can be excluded based on the genotypes observed in the paternity test.

Paternity Testing

Paternity testing involves comparing genetic markers between a child and potential fathers to establish biological relationships. In this case, the presence or absence of specific microsatellite alleles in the alleged father that match those of the child is analyzed. If the alleged father does not possess an allele that the child has inherited from the mother, he can be excluded as the biological father.