Thames & Kosmos Genetics & DNA Lab handleiding

Niet gecategoriseerd

Thames & Kosmos

52 pagina's

PDF beschikbaar

Handleiding

Chromosomes

Mendel certainly accomplished a lot, but

even after his discoveries, it wasn’t clear

where in the body the inherited programs for

our features might be located.

After about 1850, researchers working with

microscopes began to notice strange spiral

shapes in a special region of the cell that they

called the cell nucleus. Around 1880, a few of

them began to suspect that these shapes

might have some special importance. The

anatomist Wilhelm Roux (1850–1924) even

claimed in 1883 to have observed that the

strange strings were always present in pairs,

and that they were evenly and accurately

distributed between the daughter cells with

each cell division. He observed correctly.

Today we call the “sausage-like” shapes in the

cell nucleus chromosomes. They are long

threads of hereditary material, which are

rolled up with lots of twists and packaged by

the cell. There is a very simple reason for this:

If it were stretched out, the hereditary

material (like what you isolated from

tomatoes in the ﬁrst chapter) would be much

too long to be housed in a single cell. Human

DNA would be a full two meters long if

stretched out — much too long for a cell with

an average length of forty thousandths of a

millimeter, or just 0.000040 meters!

So the long thread is folded and wound up

until it ﬁts. The chromosomes that you see

here in the photos are just about four

thousandths of a millimeter long. Thus, they

easily ﬁt inside the cell.

We also just saw how we always have two

programs for any feature. In addition to that,

there is another astounding case of

symmetry: Each cell in the body always has

exactly the same number of chromosomes.

We will now determine that number.

Karyogram — graphic representation of the set

of chromosomes of a male

CHECK IT OUT

Bekijk gratis de handleiding van Thames & Kosmos Genetics & DNA Lab, stel vragen en lees de antwoorden op veelvoorkomende problemen, of gebruik onze assistent om sneller informatie in de handleiding te vinden of uitleg te krijgen over specifieke functies.