We revisit last year’s COVID-19 questions, readers weigh in on tuataras and more

Seeing double

New Zealand’s lizardlike tuatara is the first known vertebrate with two mitochondrial genomes, Devin A. Reese reported in “The tuatara hides an extra set of genes” (SN: 2/27/21, p. 10).

Reader Alfonso Solimano wondered if each mitochondrion in tuatara cells has a copy of both genomes.