Q.The diagram below shows a normal chromosome with genes in the order A B C D E F G H I, and a second chromosome with genes in the order A B B C C D E F G H I. From the above figure identify the type of mutation and explain it.

(1) extra chromosome pair = tetrasomy, (2) one extra chromosome = trisomy, (3) one chromosome lost = monosomy, (4) two chromosomes lost = double monosomy -- matching option (a).

Working

Aneuploidy is a change in chromosome number involving the gain or loss of one or a few individual chromosomes, relative to the normal diploid (2n) complement, and each specific pattern has its own name:

• Trisomy (2n+1): one single chromosome of one type is present in three copies instead of two (one extra chromosome added to the diploid set). This matches statement (2): 'one chromosome extra to the diploid.'
• Tetrasomy (2n+2): one entire homologous pair is duplicated, so one chromosome type is present in four copies instead of two (an extra PAIR of chromosomes added). This matches statement (1): 'a pair of chromosomes extra with diploid.'
• Monosomy (2n-1): one chromosome of one type is missing, leaving only a single copy instead of the normal pair. This matches statement (3): 'one chromosome loses from diploid.' …

Colchicine induces polyploidy by blocking spindle-fibre formation.

Colchicine, an alkaloid extracted from the autumn crocus (Colchicum autumnale), inhibits the polymerisation of tubulin into spindle microtubules during mitosis. When cells are treated with colchicine, chromosomes replicate normally but cannot segregate to opposite poles (no functional spindle forms), so the cell fails to divide and ends up with double the chromosome number in one …

Sugarcane's basic haploid chromosome number is 10, though cultivated canes are far more complex polyploids.

The genus Saccharum has a basic chromosome number of x=10. Saccharum officinarum itself is a natural high polyploid (about 2n=80, i.e. octoploid), and modern commercial sugarcane cultivars are complex inter-specific hybrids (Saccharum officinarum x S. spontaneum and others) with chromosome numbers commonly in t …

Nullisomy = 2n-2 (a whole homologous pair missing).

Aneuploidy is classified by how many chromosomes of one type are gained or lost relative to the normal diploid (2n) complement. In nullisomy, both members of a particular homologous pair are absent, so that chromosome type is completely missing from the genome, represented as 2n …

Double minutes are the amplified-gene chromosome fragments typical of cancer cells.

Double minutes are small, paired, acentric (lacking a centromere) extrachromosomal DNA bodies frequently observed in the karyotypes of cancer cells. They arise from gene amplification events and typically carry multiple extra copies of an oncogene (or a drug-resistance gene), contributing to uncontrolled cell proliferation or acquired drug resistance. They are distinct from polytene chromosomes ( …