In studying the crops grown by farmers in an isolated village in central Asia, you make a most remarkable discovery – a new species of wheat. As described in class, modern bread wheat is an allohexaploid carrying haploid chromosome sets from three diploid species of wild grass. These are Triticum monococcum (n=7, haploid set designated the A set), T. searsii (n=7, haploid set designated as the B set), and T tauschii (n=7, haploid set designated as the D set). To explore the origin of the new species, you cross it to each of these diploid grasses and examine the chromosome pairing arrangements of the resulting sterile F1 hybrids. The results are as follows:
Sterile F1 Hybrid Pairing Arrangement at meiosis
New species x T. monococcum 7 trivalents + 7 univalents
New species x T. searsii 14 bivalents
New species x T. tauschii 7 bivalents + 14 univalents
Deduce the chromosome constitution of the new species of wheat and fill in the blanks below. The first three fill in the blanks will help you solve the problem. Hint: only chromosomes from the same originating species will synapse at meiosis. Part of your explanation should indicate which chromosome sets are involved in each pairing arrangement above (e.g the 7 trivalents from the top F1 could be DDD and the univalents A)
How many chromosomes are in the gamete of the old world wild species? ________
How many chromosomes are in the gamete of the new species?________________
How many chromosomes do the sterile F1’s have? ______________
Chromosome constitution of the new species’ gamete is ______________________.
Therefore the constitution in its somatic cells is _____________________________.
I don't even know how to start something like this... even just explaining how to get the first blank would be greatly appreciated!!!
