Identify the organism whose genome has not been sequenced.

The correct answer is Option (4) → Sea urchin

The Human Genome Project also led to the sequencing of many non-human model organisms. These include bacteria, yeast, Caenorhabditis elegans, Drosophila, and the plants rice and Arabidopsis.

(1) Caenorhabditis elegans — A genome that has been sequenced. It is a free-living, non-pathogenic nematode.

(2) Arabidopsis — A genome that has been sequenced. It is a model plant, sequenced along with rice.

(3) Drosophila — A genome that has been sequenced. It is the fruit fly.

(4) Sea urchin — Not among the sequenced genomes. It is not among the sequenced model organisms, so it is the one that fits the question.

NCERT Extract:
Human Genome Project – “… Besides providing clues to understanding human biology, learning about non-human organisms DNA sequences can lead to an understanding of their natural capabilities that can be applied toward solving challenges in health care, agriculture, energy production, environmental remediation. Many non-human model organisms, such as bacteria, yeast, Caenorhabditis elegans (a free living non-pathogenic nematode), Drosophila (the fruit fly), plants (rice and Arabidopsis), etc., have also been sequenced.”