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?

Key Concepts

Ploidy Levels

Ploidy refers to the number of sets of chromosomes in a cell. In this case, the hexaploid line has six sets (48 chromosomes) and the tetraploid line has four sets (32 chromosomes). Understanding ploidy is crucial because it affects the fertility and viability of the offspring produced from these crosses, as mismatched ploidy levels can lead to complications in meiosis.

Chromosome Number and Fertility

Fertility in plants is often linked to the compatibility of chromosome numbers between parents. When hybrids are produced, such as the experimental varieties with 40 and 56 chromosomes, their ability to undergo meiosis and produce viable gametes can be compromised if the chromosome numbers do not allow for proper pairing and segregation during cell division.

Hybrid Vigor and Sterility

Hybrid vigor, or heterosis, can sometimes occur in hybrids, leading to increased growth or fertility. However, in cases where there is significant ploidy mismatch, such as between the hexaploid and tetraploid parents, sterility is more likely. This is due to the inability of the hybrid plants to produce balanced gametes, which can result in reduced fertility or complete sterility.