Certain varieties of chrysanthemums contain 18, 36, 54, 72, and 90 chromosomes; all are multiples of a basic set of nine chromosomes. How would you describe these varieties genetically? What feature do the karyotypes of each variety share? A variety with 27 chromosomes has been discovered, but it is sterile. Why?

The most common reason a physician might recommend that a woman have maternal serum screening and a karyotype analysis is concern that her fetus may have Down syndrome. Go to the OMIM website at www.ncbi.nlm.nih.gov/omim and look up Down syndrome (OMIM 190685).

How might those genes lead to the main symptoms of Down syndrome?

Dr. Ara B. Dopsis has an idea he thinks will be a boon to agriculture. He wants to create the 'pomato,' a hybrid between a tomato (Lycopersicon esculentum) that has 12 chromosomes and a potato (Solanum tuberosum) that has 48 chromosomes. Dr. Dopsis is hoping his new pomato will have tuber growth like a potato and the fruit production of a tomato. He joins a haploid gamete from each species to form a hybrid and then induces doubling of chromosome number.

Can Dr. Dopsis be sure the polyploid will have the characteristics he wants? Why or why not?

Dr. Ara B. Dopsis has an idea he thinks will be a boon to agriculture. He wants to create the 'pomato,' a hybrid between a tomato (Lycopersicon esculentum) that has 12 chromosomes and a potato (Solanum tuberosum) that has 48 chromosomes. Dr. Dopsis is hoping his new pomato will have tuber growth like a potato and the fruit production of a tomato. He joins a haploid gamete from each species to form a hybrid and then induces doubling of chromosome number.

How many chromosomes will the polyploid have after chromosome doubling?

The primrose, Primula kewensis, has 36 chromosomes that are similar in appearance to the chromosomes in two related species, P. floribunda (2n=18) and P. verticillata (2n=18). How could P. kewensis arise from these species? How would you describe P. kewensis in genetic terms?

In Drosophila, seven partial deletions (1 to 7) shown as gaps in the following diagram have been mapped on a chromosome. This region of the chromosome contains genes that express seven recessive mutant phenotypes, identified in the following table as a through g. A researcher wants to determine the location and order of genes on the chromosome, so he sets up a series of crosses in which flies homozygous for a mutant allele are crossed with flies homozygous for a partial deletion. The progeny are scored to determine whether they have the mutant phenotype ('m' in the table) or the wild-type phenotype ('+' in the table). Use the partial deletion map and the table of progeny phenotypes to determine the order of genes on the chromosome.

Two experimental varieties of strawberry are produced by crossing a hexaploid line that contains 48 chromosomes and a tetraploid line that contains 32 chromosomes. Experimental variety 1 contains 40 chromosomes, and experimental variety 2 contains 56 chromosomes.

Do you expect both experimental lines to be fertile? Why or why not?

Two experimental varieties of strawberry are produced by crossing a hexaploid line that contains 48 chromosomes and a tetraploid line that contains 32 chromosomes. Experimental variety 1 contains 40 chromosomes, and experimental variety 2 contains 56 chromosomes.

How many chromosomes from the tetraploid lines are contributed to experimental variety 1? To experimental variety 2?

Two experimental varieties of strawberry are produced by crossing a hexaploid line that contains 48 chromosomes and a tetraploid line that contains 32 chromosomes. Experimental variety 1 contains 40 chromosomes, and experimental variety 2 contains 56 chromosomes.

How many chromosomes from the hexaploid line are contributed to experimental variety 1? To experimental variety 2?