little
/ˈlɪt̬.əl/
adjective , lit·tler or less or less·er, lit·tlest or least.

small in size; not big; not large; tiny: a little desk in the corner of the room.
short in duration; not extensive; short; brief: a little while.
small in number: a little group of scientists.

extra
/ˈek.strə/
adjective

beyond or more than what is usual, expected, or necessary; additional: an extra copy of a newspaper; an extra charge.
larger or better than what is usual: an extra binding.

Origin of extra
First recorded in 1770–80; by shortening of extraordinary

chromosome
/ˈkroʊ.mə.soʊm/
noun Genetics.

any of several threadlike bodies, consisting of chromatin, that carry the genes in a linear order: the human species has 23 pairs, designated 1 to 22 in order of decreasing size and X and Y for the female and male sex chromosomes respectively.