We now want to take a closer look at polyploidy. Polyploidy, as we said, is technically more complex. So we want to go through it more slowly here. It's unlikely that you'll need to be responsible for all these technical details, but we want to show them to you just so that you understand how it works. Remember that polyploidy, as we said, involves having extra sets of chromosomes.

If your normal cell is diploid, it has 2 sets of chromosomes. A tetraploid cell, which is a polyploid cell, will have 4 sets of chromosomes, twice the normal amount. Strawberries are octaploid; they have 8 complete sets of chromosomes. When a cell becomes polyploid, it can create a new species in a single generation. This occurs because having extra sets of chromosomes leads to speciation. Species with different numbers of chromosomes trying to reproduce together may create sterile hybrids, if those hybrids are viable at all.

To see how polyploidy works, let's consider two basic types: autopolyploidy and allopolyploidy. Starting with autopolyploidy, the prefix 'auto' means self. Autopolyploidy is created through a cell division error within a species or within a single organism. This is rarer, but let's explore how it works. Consider a diploid cell with 2n = 6 chromosomes. If this cell experiences a cell division error, the total number of chromosomes might double, resulting in a tetraploid cell with 4n = 12 chromosomes.

This organism, when it undergoes meiosis, will produce diploid gametes (2n = 6) instead of the typical haploid gametes. The challenge is finding a compatible mate since no other organisms have diploid gametes. However, if this organism can self-fertilize, the diploid gametes will fuse, recreating a tetraploid zygote (4n = 12). This new zygote can grow into an organism and reproduce, thereby creating a new species with a new number of chromosomes in a single generation. This ability to self-fertilize is why polyploidy is more common in plants, though it can occur in other organisms.

Turning to allopolyploidy, 'allo' means different. Allopolyploidy arises through hybridization between two different species, followed by a cell division error. Consider two species: Species 1 is diploid with 4 chromosomes, and Species 2 is diploid with 6 chromosomes. Through meiosis, these species produce normal haploid gametes. The gamete from Species 1 has two chromosomes, and from Species 2, three chromosomes.

When these gametes fuse, they may form a hybrid, likely a sterile one because the parental chromosomes differ in number. This hybrid isn't technically diploid because the chromosomes from each parent don't pair properly, resulting in a genome where n = 5. If a cell division error occurs afterward, we end up with a diploid organism that has 10 chromosomes, forming an allopolyploid. This allopolyploid can self-fertilize. Here, we have complete DNA sets from two different species and two of each chromosome, effectively doubling the DNA while maintaining a diploid state.

While these details might be more than you need to know, here’s what you probably really need to remember: Autopolyploidy results in polyploid organisms within a single species. Allopolyploidy starts with a hybridization event followed by a cell division error, leading to extra DNA. More lessons and practice are coming up, and I'll see you there.