A generation ago genetic codes were certainly unknown.是什么意思？

A generation ago genetic codes were certainly unknown.

遗传密码在上一代确实很少有人知道.

generation

n. 一代人，代（约30年），时代，生殖，产生；

例句
...the picture of the Earth, so blue and fragile, that awakened a generation to the Earth's mortality.
照片上的地球，如此的忧郁而脆弱，唤起了一代人对地球生命的意识

ago

adv. 以前，过去的，之前；

例句
He was killed a few days ago in a skiing accident...
几天前他在一场滑雪事故中丧生。

genetic

adj. 遗传的，基因的，起源的，起因的，演变的；

例句
The offspring contain a mixture of the genetic blueprint of each parent...
子女身上遗传了父母双方的基因型板。

codes

n. [计算机]编码( code的名词复数 )，代号，密码，法典；

例句
A generation ago genetic codes were certainly unknown.
遗传密码在上一代确实很少有人知道.

were

be的过去时复数和第二人称单数形式，有时代替 was,用于条件从句、动词 wish 之后等；

例句
Shops, houses, and vehicles were set ablaze.
店铺、房子和车辆全都陷于火海。

certainly

adv. 无疑，当然，确定，肯定；

例句
The Party was certainly not an official adjunct of the police department.
该党派肯定不是公安部门的官方附属机构。

unknown

adj. 未知的，不出名的，从未发生的，从不存在的；n. 不知名或不出名的人，未知的事物，<数>未知数，未知数；

例句
It is not unknown for valuable display items to go, ahem, missing.
贵重的展品，呃哼，丢失的话，会众人皆知。