After having run over 90,000 samples, they have a lot of experience reading these results. The probe seeks out the complimentary strands of DNA and bonds to it. They know what the probe is and the places to which it will bond. Those places are associated with pieces of DNA on the bird's sex chromosomes. The last step is to expose x-ray film to the nylon membrane containing the radioactive probe.
Dark bands develop at the probe sites.
The resulting X-ray is a pattern which can be interpreted by technicians. The pattern of these bands reveal the sex of your bird. Many animals, including humans, have a pair of sex chromosomes, designated X and Y, that determine an individuals sex. In humans, individuals with XY chromosomes are male and XX chromosomes are female. These are the chromosomes used in the DNA sequence probe to determine the sex of a bird.