Chromosomes are thread-like structures located inside the nucleus of animal and plant cells. Each chromosome is made of protein and a single molecule of deoxyribonucleic acid (DNA). Passed from parents to offspring, DNA contains the specific instructions that make each type of living creature unique.

2. .
GPB 2.2 FUNDAMENTALS OF GENETICS
Dr. D. K. Patel
Assistant Professor
Department of Genetics & Plant breeding
Faculty of Agriculture

3.  They are the carriers of the gene
or unit of heredity.
 Chromosome are not visible in
active nucleus due to their high
water content, but are clearly seen
during cell division.
What is chromosome?
“Chromosomes are the rod-shaped, filamentous bodies
present in the nucleus, which become visible during cell
division”

4. About History
 Chromosomes were first described
by Strausberger in 1875.
 The term “Chromosome”, however
was first used by Waldeyer in 1888.
Chromosome (Chromo means colour
and Soma means body).

5. Number of chromosomes
 Normally, all the individuals of a species have the same
number of chromosomes.
 Closely related species usually have similar chromosome
numbers.
 Presence of a whole sets of chromosomes is called euploidy. It
includes haploids (n), diploids (2n), triploids (3n), tetraploids
(4n) etc.
 Gametes normally contain only one set of chromosome – this
number is called Haploid

6. Table 1 : Chromosome numbers in some organisms
Common Name Scientific Name 2n N
Round worm Ascaris megalocephala 2 1
Fruit fly Drosophila melanogaster 8 3
Grasshopper Melanoplus differentialis 24 12
Frog Rana pipiens 26 13
Honey bee Apis mellfera 32 16
Cat Felis domesticus 38 19
Rat Rattus norvegicus 42 21
Man Homo sapiens 46 23
Gorilla Gorilla gorilla 48 24
Chimpanzee Pan troglodytes 48 24
Cattle Bos taurus 60 30
Donkey Equus asinus 62 31
Horse Equus calibus 64 32
Dog Canis familiaris 72 39

7. Common Name Scientific Name 2n n
Haplopappus gracilis 4 2
Crepis capillaris 6 3
Broad bean Vicia laba 12 6
Barley Hordeum vulgare 14 7
Rye Secale cereale 14 7
Peas Pisum sativum 14 7
Pearl millet Pennisetum americanum 14 7
Onion Allium cepa 16 8
Gram (Chickpea) Cicer arietinum 16 8
Maize Zea mays 20 10
Jowar Sorghum bicolor 20 10
Pigeon Columba livia 80 40

8. Common Name Scientific Name 2n n
Kidney bean Phaseolus vulgaris 22 11
Pigeon pea Cajanus cajan 22 11
Rice Oryza sativa 24 12
Durum wheat Triticum durum 28 14
Bread wheat Triticum aestivum 42 21
Potato Solanum tuberosum 48 24
Tobacco Nicotiana tabacum 48 24
Upland cotton Gossypium hirsutum 52 26
Fern Ophioglossum reticulatum 1260 630

9.  There is wide variation in the chromosome numbers of different plant
and animal species.
 Haplopappus gracilis (family Asteraceae) contains only two pairs of
chromosomes (2n = 4), while the plant Ophioglossum reticulatum (a
fern) contains 630 pairs (2n = 1260) of chromosomes in its somatic
cells.
 In animals, the lowest chromosome number has been reported in the
round worm (Ascaris megalocephala) and Geratrix hennaphroditus
(both 2n = 2; n = 1). On the other extreme, some protozoa possess upto
1600 chromosomes.

10. Chromosome Size
The size of chromosomes shows a remarkable
variation depending upon the stages of cell
division.
• Interphase: chromosome are longest & thinnest
• Prophase: there is a progressive decrease in their
length accompanied with an increase in
thickness
• Anaphase: chromosomes are smallest.
• Metaphase: Chromosomes are the most easily
observed and studied during metaphase when
they are very thick, quite short and well spread in
the cell.

11. • In general, plants have longer chromosomes than
animal and species having lower chromosome
numbers have long chromosomes than those having
higher chromosome numbers
• Among plants, dicots in general, have a higher number
of chromosome than monocots.
• Chromosomes are longer in monocot than dicots.

12. CHROMOSOME MORPHOLOGY
(1) Chromatid
(2) Centromere
(3) Telomere
(4) Secondary constriction and satellite
(5) Chromomere

13. Morphology of Chromosomes

14. 1. Chromatid
 Each metaphase chromosome appears to be
longitudinally divided into two identical
parts each of which is known as chromatid.
 The two chromatids of a chromosome appear
to be 'joined' or 'fused' together at a point
called centromere.
Chromatid

15. 2. Centromere
 The region where the two sister chromatids of
a chromosome appear to be 'joined' or 'held
together' during mitotic metaphase is known
as centromere.
 Under light microscope, centromere generally
appears as a constriction (a narrowed region)
in the chromosome, hence it is also termed as
primary constriction.
 When chromosomes are stained they typically
show a light-stained region that is the
centromere.

16.  Chromosomes may be divided into four classes
on the basis of the position of their centromeres:
(1) Metacentric
(2) Submetacentric
(3) Acrocentric
(4) Telocentric.

17. (a) Metacentric:
 In such chromosomes, the
centromere position is either
exactly at the middle (median) or
near the middle region (median
region) of the chromosomes.
 Both the chromosome arms are
nearly or quiet equal in length.
 At anaphase, the chromosomes
take the typical V-shape, the
centromere being at the apex of V.

18. (b) Submetacentric:
 The centromere position in
submetacentric chromosomes is
submedian so that their two arms
are distinctly unequal.
 The chromosomes take a J or L-
shape at anaphase.

19. (c) Acrocentric:
 Centromere position is near the
end.
 One arm is long while the other
is very short.

20. (d) Telocentric:
 Centromere of such
chromosomes is located at one
end of the chromosome, i.e., it
has a terminal position; such
chromosomes consist of a
single arm.
 Telocentric chromosomes
appear rod-shaped during
anaphase.

21. 3.Telomere
 The two ends of a chromosome are known
as telomere.
 Telomeres are highly stable and they do
not fuse or unite with telomeres of other
chromosomes.
 When telomeres are damaged or removed
due to chromosome breakage, the damaged
chromosome ends are highly unstable and
such ends readily fuse or unite with broken
ends of other chromosomes.

22. 4. Secondary Constriction
 Certain chromosomes have one or more non-centromeric
“secondary constrictions”, in addition to their primary
constrictions.
 The Region between the secondary constrictions and nearest
telomere known as satellite and that chromosome known as
satellite chromosome.
 Nucleolus always associated with secondary constriction also
called as nuclear organizer region (NORs) and chromosome
called as nuclear organizer chromosome (NOC)

23. 5. Chromomere
 In some species, e.g., maize, amphibia etc., chromosomes
during the first prophase of meiosis, more particularly during
pachytene, show small bead-like structures called
chromomeres.
 The distribution of chromomeres in a chromosome is highly
characteristic and constant, the patterns of distribution being
different for different chromosomes; homologous chromosomes
show an identical pattern.
 Chromomeres are most clearly visible in the dipteran giant
salivary gland chromosomes as dark staining bands.

24. KARYOTYPE
 The general morphology, i.e., the size of chromosomes, the
position of centromeres, the presence of secondary constrictions
and the size of satellite bodies of the somatic chromosome
complement of an individual constitutes its karyotype.
 Ordinarily, karyotypes are presented by arranging the
chromosomes of somatic complement in a descending order of
size keeping their centromeres in a straight line; thus the longest
chromosome is placed on the extreme left and the smallest one on
the extreme right.

25. • Karyotype: is the general morphology of the somatic
chromosome. Generally, karyotypes represent by
arranging in the descending order of size keeping
their centromeres in a straight line.
• Idiogram: the karyotype of a species may be
represented diagrammatically, showing all the
morphological features of the chromosome; such a
diagram is known as Idiogram.

27.  Provide the genetic information for various cellular
functions.
 Protect the genetic material (DNA)
 Precise distribution of DNA
 Chromosome movement during cell division
 Regulation of gene action