The document discusses euploidy, or changes in the number of sets of chromosomes, in animals and plants. It notes that while most animal species are diploid, some natural variations exist, including polyploidy in certain tissues and endopolyploidy. Polyploidy is more common and tolerated in plants, with 30-35% of ferns and flowering plants being polyploid. Examples are given of polyploid crops like wheat, cotton, and strawberries that are important agricultural products.

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 Most species of animals are diploid
 In many cases, changes in euploidy are not tolerated
 Polyploidy in animals is generally a lethal condition
 Some euploidy variations are naturally occurring
 Female bees are diploid
 Male bees (drones) are monoploid
 Contain a single set of chromosomes
EUPLOIDY

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 In many animals, certain body tissues display normal
variations in the number of sets of chromosomes
 Diploid animals sometimes produce tissues that are
polyploid
 This phenomenon is termed endopolyploidy
 Liver cells, for example, can be triploid, tetraploid or even
octaploid (8n)
 Polytene chromosomes of insects provide an
unusual example of natural variation in ploidy
EUPLOIDY

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 Occur mainly in the salivary glands of Drosophila
and a few other insects
 Chromosomes undergo repeated rounds of
chromosome replication without cellular division
 In Drosophila, pairs of chromosomes double approximately
nine times (29 = 512)
 These doublings produce a bundle of chromosomes
that lie together in a parallel fashion
 This bundle is termed a polytene chromosome
POLYTENE CHROMOSOMES

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 Because of their size, polytene chromosomes lend
themselves to an easy microscopic examination
 They are so large, they can be even seen in interphase
 Polytene chromosomes exhibit a characteristic
banding pattern
 Each dark band is known as a chromomere
 The DNA within the dark band is more compact than that in the
interband region
 Cytogeneticists have identified about 5,000 bands

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 In contrast to animals, plants commonly exhibit
polyploidy
 30-35% of ferns and flowering plants are polyploid
 Many of the fruits and grain we eat come from polyploid
plants
 In many instances, polyploid strains of plants display
outstanding agricultural characteristics
 They are often larger in size and more robust
EUPLOIDY

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 Sterility is generally a detrimental trait
 However, it can be agriculturally desirable because it
may result in
 1. Seedless fruit
 Seedless watermelons and bananas
 Triploid varieties
 Asexually propagated by human via cuttings
 2. Seedless flowers
 Marigold flowering plants
 Triploid varieties

7. POLYPLOID CROPS
• Examples of polyploid crops
• Triploid crops: apple, banana, citrus, ginger,
watermelon
• Tetraploid crops: apple, durum or macaroni wheat,
cotton, potato, cabbage ,leek, tobacco, peanut,
kinnow, Pelargonium
• Hexaploid crops: chrysanthemum, bread wheat,
triticale, oat, kiwifruit
• Octaploid crops: strawberry

8. AUTOPOLYPLOIDY
• Artificially induced: chloral hydrate,colchicine,mercury chloride
• Prevent mitotic/meiotic spindle fibres
• Colchinine : prevent formation of spindle fibre
• Arrest at metaphase stage
• No alignment at metaphase stage
• Prevention of cytokinesis

9. AUTOPOLYPLOIDY
• Effects: gigantism in plants (leaves,flowers,fruits)
• > in water content
• < in auxin supply
• < in respiration

10. ALLOPOLYPLOIDY
• Triticum spelta : hexaploid wheat
• Wheat(T.dicoccoides) * Grass(Aegilops squarrosa)
• 2n=28 * 2n=14
• Treated with colchicine –T. spelta
• 2n=42(artificial wheat )
• six similar sets of seven chromosomes

11. ALLOPOLYPLOIDY
• Gossypium hirsutum(new world cotton plant)
• Old world cotton * American cotton
• 13pairs (2n=26)* 13 pairs(2n=26)
• Colchicine treatment
• 2n=52

12. POLYPLOIDS
• Apples
• Mostly diploid
• Gravenstein' apples
• triploid chromosome number of 51 (3n=51)
• produced by the union of a diploid egg
(2n=34) and a haploid sperm (n=17).

13. GRAVENSTEIN APPLES
• (3n) varieties are sterile are propagated by grafting
• grafted to hardy,pest-resistant root stalks.

14. TRIPLOID WATERMELON
• Seedless
• highly sterile triploid (3N) plants
• produces triploid flowers
• flowers do not produce pollen or eggs

15. RABBAGE
• bigeneric hybrid(Raphanobrassica)
• cross between the radish (Raphanus, 2n=18) and
cabbage (Brassica,2n=18).

17. turnip rutabaga cabbage
n=10 4n=38 n=9
10 + 10
9 + 9