When it comes to karyotypes, why do the chromosomes have to be arranged from largest to smallest?
I'd assume that chromosomes labelled 1 through 22 are based on size. By labelling them from largest to smallest, you can easily identify which is chromosome 1, 2, etc. The 23rd pair are the sex chromosomes, they're arranged at the end. If it's a female, they'll match, if a male, they don't.
From my research, the chromosomes are cut out and arranged according to a convention, called the
Denver classification, that was established by a group of geneticists.
Table
of Denver Chromosome Classification
|
Chromosome
Group
|
Chromosome
number
|
Description
of chromosomes
|
A
|
1
- 3
|
Large,
metacentric
|
B
|
4
- 5
|
Large,
submetacentric
|
C
|
6
- 12
|
Medium-sized,
submetacentric; X chromosome closely resembles pair number 6, longest in
group
|
D
|
13
- 15
|
Medium-sized,
acrocentric; all three pairs with satellites on short arm
|
E
|
16
- 18
|
Smallest
of the medium-sized; pair 16 metacentric; others submetacentric
|
F
|
19
- 20
|
Short,
metacentric
|
G
|
21
- 22
|
very
short; acrocentric; both with satellites
|