Question

The common bread wheat has chromosomes –
A) $14$
B) $21$
C) $28$
D) $42$

Answer 1

Hint: Triticum aestivum or Triticum vulgare is common bread wheat. It is hexaploid i.e. it has hexaploid genome.

Complete Answer:
– As bread wheat has hexaploid genome. It means it has six copies of each of its seven chromosomes, the complete set numbering is $42$ chromosomes.
– Hexaploid T. aestivum originated some $6000 - 7000$ years ago.
– Common bread wheat is the example of allopolyploidy.
– If an organism possesses more than two sets of chromosomes are called polyploids.
– The polyploids arise as a result of chromosome doubling following hybridization of two distinctly different species called allopolyploids.
– Triticum aestivum is developed by the hybridization of the Emmer Wheat (Triticum turgidum) with wild grass (Triticum tauschii or Aegilops squarrosa).
– This hybridization produces a hybrid with three sets of chromosomes $(ABD = 21)$. This hybrid was also sterile.
– However, sometime during evolution these sterile hybrids underwent doubling of the chromosomes and resulted in the formation of present day hexaploid $(AABBDD = 42)$ i.e. Bread wheat.

The correct option is D.

Note:

Triticum turgidum (Emmer wheat) $(2N = 28\;AABB)$(Tetraploid)

Triticum tauschii or Aegilops squarrosa(Wile grass)$(2N = 14\;DD)$(Diploid)

       

Sterile Triploid $(ABD = 21)$Chromosome doublingTriticum aestivum (Common bread wheat)$(2N = 42,\;AABBDD,\;Hexaploid)$