The most difficult DNA riddles

Trisomy 13, also called Patau syndrome, is a chromosomal condition associated with severe intellectual disability and physical abnormalities in many parts of the body. Individuals with trisomy 13 often have heart defects, brain or spinal cord abnormalities, very small or poorly developed eyes

Interbreeding between Neanderthals with modern humans took place several times. Neanderthal-derived DNA was found in the genome of contemporary populations in Europe and Asia, it accounts for 1–4% of modern genomes. Neanderthal genes are absent from most modern populations in sub-Saharan Africa.

The cultivated kiwi fruit, Actinidia deliciosa, is a hexaploid species with a total number of 174 chromosomes. Many of cultivated plants are polyploids created by selective breeding, and are usually unable to interbreed with their diploid ancestors.

A prion is composed of protein in a misfolded form. When a prion enters a healthy organism, it induces existing, properly folded proteins to convert into the disease-associated, prion form; the prion acts as a template to guide the misfolding of more proteins into prion form.

Uracil is one of the four nucleobases in the nucleic acid of RNA that are represented by the letters A, G, C and U. The others are adenine (A), cytosine (C), and guanine (G). In RNA, uracil binds to adenine via two hydrogen bonds. In DNA, the uracil nucleobase is replaced by thymine. Uracil is a demethylated form of thymine.