The threads within the nucleus of a cell which become visible during cell division. The chromosomes were postulated to be the carriers of inherited information in 1903, after a study of the close correspondence between their behaviour and Mendelian factors. Chromosomes occur in pairs - one member of maternal and one of paternal origin. They are the major carriers of genetic material, consisting of chromatin (DNA and various types of proteins, mostly histones). The position of a particular gene on a chromosome is called its locus. The number of chromosomes differs from species to species. A normal human cell has 46 chromosomes: 22 pairs of autosomes together with (in females) one matching pair of X chromosomes and (in males) one nonmatching pair, the X and Y chromosomes. By the end of 2003, the genetic map of four human chromosomes (14, 20, 21, 22) had been published.
Number of chromosomes in various species
Chromosome numbers in some animals
|
Species
|
#
|
Species
|
#
|
|
Fruit fly
|
8
|
Guinea Pig
|
16
|
|
Dove
|
16
|
Snail
|
24
|
|
Earthworm
|
36
|
Tibetan fox
|
36
|
|
Cat
|
38
|
Pig
|
38
|
|
Mouse
|
40
|
Rat
|
42
|
|
Rabbit
|
44
|
Syrian hamster
|
44
|
|
Hare
|
46
|
Human
|
46
|
|
Gorilla
|
48
|
Sheep
|
54
|
|
Elephant
|
56
|
Cow
|
60
|
|
Donkey
|
62
|
Horse
|
64
|
|
Dog
|
78
|
Chicken
|
78
|
|
Carp
|
104
|
Butterflies
|
380
|
Chromosome numbers in some plants
|
Plant Species
|
#
|
|
Arabidopsis
|
10
|
|
Rye
|
14
|
|
Maize
|
20
|
|
Einkorn wheat
|
14
|
|
Pollard wheat
|
28
|
|
Bread wheat
|
42
|
|
Wild tobacco
|
24
|
|
Cultivated tobacco
|
48
|
|
Fern
|
1200
|
Normal members of a particular species all have the same number of chromosomes (see the table). In females, one of the two X chromosomes is inactive and can be seen under a microscope as Barr
bodies.
Human
|
Chromosome
|
Genes
|
Bases
|
Determined basesâ€
|
|
1
|
2968
|
245,203,898
|
218,712,898
|
|
2
|
2288
|
243,315,028
|
237,043,673
|
|
3
|
2032
|
199,411,731
|
193,607,218
|
|
4
|
1297
|
191,610,523
|
186,580,523
|
|
5
|
1643
|
180,967,295
|
177,524,972
|
|
6
|
1963
|
170,740,541
|
166,880,540
|
|
7
|
1443
|
158,431,299
|
154,546,299
|
|
8
|
1127
|
145,908,738
|
141,694,337
|
|
9
|
1299
|
134,505,819
|
115,187,714
|
|
10
|
1440
|
135,480,874
|
130,710,865
|
|
11
|
2093
|
134,978,784
|
130,709,420
|
|
12
|
1652
|
133,464,434
|
129,328,332
|
|
13
|
748
|
114,151,656
|
95,511,656
|
|
14
|
1098
|
105,311,216
|
87,191,216
|
|
15
|
1122
|
100,114,055
|
81,117,055
|
|
16
|
1098
|
89,995,999
|
79,890,791
|
|
17
|
1576
|
81,691,216
|
77,480,855
|
|
18
|
766
|
77,753,510
|
74,534,531
|
|
19
|
1454
|
63,790,860
|
55,780,860
|
|
20
|
927
|
63,644,868
|
59,424,990
|
|
21
|
303
|
46,976,537
|
33,924,742
|
|
22
|
288
|
49,476,972
|
34,352,051
|
|
X (sex chromosome)
|
1184
|
152,634,166
|
147,686,664
|
|
Y (sex chromosome)
|
231
|
50,961,097
|
22,761,097
|
|
unplaced various
|
?
|
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