In the plant genus Triticum there are many different polyploid species and also
ID: 74578 • Letter: I
Question
In the plant genus Triticum there are many different polyploid species and also diploid species. Crosses were made between some different species, and hybrids were obtained. The meiotic pairing was observed in each hybrid and is recorded in the table below. Note that a bivalent is two homologous chromosomes paired at meiosis, and a univalent is an unpaired chromosome at meiosis.
Species crossed to make the hybrid
Chromosome pairing in hybrid T. turgidum X T. monococcum 7 bivalents + 7 univalents T. aestivum X T. monococcum 7 bivalents + 14 univalents T. aestivum X T. turgidum 14 bivalents + 7 univalents
a. Deduce the somatic chromosome number of each species used.
b. State which species are polyploid and whether they are auto or allopolyploid.
c. Account for the chromosome pairing pattern in the three hybrids.
Explanation / Answer
a. somatic chromosome number:
T. turgidum: 2n=4x= 28 (tetraploid)
T. monococcum: 2n=2x= 14 (diploid)
T. aestivum: 2n= 6x=42 (hexaploid)
b. T. aestivum is an autohexaploid;
T. turgidum is an autotetraploid
c. i) T. turgidum X T. monococcum
AABB x AA
ii) T. aestivum X T. monococcum
AABBDD x AA
iii) T. aestivum X T. turgidum
AABBDD x AABB
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