2. WHAT IS CHROMOSOMAL VARIATION ????
HOW IT OCCURS……..?
Error during cell division, replication, crossing over
Cause variation in structure and number
6. POLYPLOIDS
PLOIDY - the number of sets of chromosomes in cell,
or in the cells of an organism
POLPLOIDY - more than two sets of chromosomes are present
polyploidy
autopolyploid
Addition of one
more extra sets of
chr. From same spp.
allopolyploidy
Combination of chr.
sets b/w different
spp.
10. Autotetraploids
produced experimentally by
• cold/heat shock to meiotic cells
• colchicine treatment to somatic cells
Chromosome replicated no cell division reenters interphase
chromosome number douled
The autopolploids are relatively larger than their diploid relatives,
this increased size making them with greater commercial or
horticultural value.
13. How the cells increases in size??????
Gerald Fink study on Saccharomyces cerevisiae
G1 CYCLINS
14. GENETIC RATIOS PRODUCED BY TETRAPLOIDS
Assume that, the tetraploids only produce bivalents.
If we start with an A/A/a/a tetraploid plant and self it,
what proportion of progeny will be a/a/a/a ?
16. Origin of three alloploid species o Brassica
Allopolyploidy is important in the production o new species. In the example shown, three diploid species of
Brassica (light green boxes) we crossed in different combinations to produce their allopolyploids(tan
boxes).some of the agricultural derivatives of some species are shown within the boxes.
