Describe the sources of diversity.

1.Mendelian changes
? Plants mutated from the wild for domestication
? There was segregation and recombination hence getting new genetic material. These changes have a way of being preserved in the organism.
Stabilizing factors of evolution
? If environment does not change over thousands of years (stable environment)
? If cultivation doesn’t change over a long time. e.g. growing same variety – stable cultivation practices.
? If cultivation covers large areas of land over time and space
If equilibrium of the 3 factors is upset, evolution /changes will occur. e.g. of crops evolved e.g. Barley, Maize, Soya beans, Common bean, sugar beet.
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Barley: - The crop has changed over time into various uses and various fitness to fit different ecologies. It has had both anatomical and morphological changes over time was domesticated in 700 B.C. The present barley Hordeum Vulgare. It changed from the wild Hordem spontaneous through evolution
Difference: The domesticated type had a tougher rachis than wild type.
Domesticated type had non-shattering grains, wild –shattered
Wild type had two vows on head, domesticated had 6 rows on head. From middle East, the Barley origin, it went to Egypt (Barley of the Nile) then to Europe and diversified as food, feed, brewing type and then spread to Africa. Also gave different morphological types: 2 rows and 6 rows

2. INTERSPECIFIC HYBRIDIZATION
Inter –between Specific species
This is the hybridization between species. is not normal but may happen between genera that are closely related It normal takes places between same species Horse + donkey = Mule (sterile)
Two species can be hybridized but this is rare. When it occurs, the progeny is sterile. If not sterile, it will not be useful. However very rarely we find useful hybrids between species.
In plants, the progeny can be useful. They can be propagated vegetatively if there are no seeds and the cross may be useful in nature, we have 3 major crops that were produced by inter-specific hybridization (naturally) –strawberry, maize , sorghum.
Two species strawberry were Fragaria chiloencis x Fragaria Viginia
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Qualities of Pacific
? Superior fruit
? quality flesh
? Attractive flavour
Progeny produced was the modern day strawberry which combined all the 5 qualities. It usually propagated by cutting, don’t have fertile seeds.
This system is useful in fundamental crops and horticultural crop.
Maize
Believed to have been crossed by two relatives
Wild maize (Teosinte) and Tripsacum are found as weeds in Mexico where maize originated. The two crossed through introgression – series of crosses that led to more of the original. Very little of Teosinte was in the progeny
Modern maize has a bit of Feosinite but more of Tripsacum.
Sorghum – Evolved in the Savannah (African)
A grass crossed with wild sorghum and backcrossing occurred.

3. AUTOPLOIDY – Doubling of chromosis the same species
Genome having same Xsome No.
Basic genomic no = X (when there is no doubling – haploid
2 x (double) diploid (somatic no)
The chromosome no. can go up e.g. instead of 2 x = 4x or 6 x
E.g. species
somatic no. 2n = 2x
at time doubling
in the progreny, haploid No. 28 is divided during mitosis to give 14.
e.g. Bread wheat
Polyploidy – When there are more than 2 sets of chromosomes
n= haploid
2n = diploid
3n = triploid e.g. bananas
Polyploids are dividend into 2
Triploid – Doubling of xSome no of the same species
Copying of chromosomes lowest 2 n + n = 3 n e.g. Banana , that’s why the banana is seedless.
Astoploid - Doubling of xsomes in the same species e.g. alfalfa (licence) The xsomes in the same species e.g.
Alloploidy – Doubling in sets chromosomes different species Both autoploids and alloploids are polyploids. e.g. Tetraploids – Grapes, Apple, Pears, Tomatoes and several flowers (Natural)

4. Alloploidy
Involves more than 1 species e.g. wheat (3 species), cotton 2 species Cotton 2 species cotton Grossypium
Species – G. Herbaceum – Originated African Asian
Had 3 parts of Xsome (Large)
was a diploid , genome designeated AA
Species G. Raimondi –Origin Resus (Pesuvian)
Had 13 pars (small) chromosomes
Genome designated DD and are diploid
These 2 crossed in nature through segregation (mitosis) Gare progeny AD which would be sterile but the Chromosomes no doubled in nature which is then productive after merosis.
AA x DD
A x D
AD
AADD (doubled) Each xsome has its partners and gets fertile
Therefore we get a plant with double xsome no. 26 (haploid). That how the current cotton came into being.
The 3 wheats are diploids and still in the wild Tetraploid wheat = e.g. macasoni
Hexaploid wheat = cultivated Bread wheat

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Kavungya answered the question on March 12, 2019 at 07:18