In the plant genus Triticum there are many different polyploid species, as well
ID: 86288 • Letter: I
Question
In the plant genus Triticum there are many different polyploid species, as well as diploid species. Crosses were made between three different species, and hybrids were obtained. The meiotic pairing was observed in each hybrid, and this is recorded in the following table.
Species crossed to make hybrid
Pairing in hybrid F1 meiosis
Cross 1. T. durts × T. mono
7 bivalents + 7 univalents
Cross 2. T. tivum × T. mono
7 bivalents + 14 univalents
Cross 3. T. tivum × T. durts
14 bivalents + 7 univalents
a) Using the information gathered from the crosses above, deduce the F1 chromosome number (ploidy) from each cross.
b) Using the information gathered from the crosses above, deduce the somatic chromosome number of each parent species used.
c) State which species are polyploid and whether they are autopolyploids or allopolyploids.
d) Describe how the observed chromosome pairing pattern arose in the the F1 of Cross 1.0.
Species crossed to make hybrid
Pairing in hybrid F1 meiosis
Cross 1. T. durts × T. mono
7 bivalents + 7 univalents
Cross 2. T. tivum × T. mono
7 bivalents + 14 univalents
Cross 3. T. tivum × T. durts
14 bivalents + 7 univalents
Explanation / Answer
(a) 1 must be 2n ´ 4n with one set of seven chromosomes in common
2 might be 2n ´ 6n with 1 set of seven chromosomes in common
3 must be 4n ´ 6n with 2 common sets of seven chromosomes
Putting these together:
T. mono = AA (2x = 14)
T. durt = AABB (4x = 28)
T. tivum = AABBCC (6x = 42)
(b) T. durt and T. tivum are allopolyploids.
(c) When T. mono is crossed with T. durt an A gamete combines with an AB gamete so that in the hybrid the two A sets pair and the B has no pairing partner. The other pairings follow the same logic.
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