Looking for patterns, trends and discrepancies—patterns of chromosome number in some genera can be explained by speciation due to polyploidy.
Polyploidy is a condition of possessing more than two sets of chromosomes. This duplication typically occurs during meiosis and may result in triploid (3n), tetraploid (4n) or even hexaploid (6n) offspring. This sounds potentially devastating (think of the effects of just having one extra chromosome!) but is thought to be a key driving factor in speciation in some organisms. Up to 1 in 100,000 flowering plants are polyploid, showing a high degree of tolerance. In fact, over 75% of flowering plant species may be recent polyploids! Common polyploids include potatoes, bananas, cotton, wheat and watermelon.
Although it also can occur in amphibians and fish, mammals and birds are typically less tolerant, with an estimate of 10% of spontaneous miscarriages in humans being due to polyploid embryos (Woodhouse et. al.).
The advantages of polyploidy include:
- The extra sets of alleles mean that the offspring is less likely to be affected by recessive mutations
- it promotes heterozygosity, which can make the hybrid offspring more fit than the parents
- the extra sets of genes may evolve new functions over time
- it seems to increase asexual reproductive ability, which could be advantageous under some conditions.
Potential disadvantages include:
- the extra genetic material affects the surface area to volume ratio of the nucleus and the cell, disrupting many important processes
- disruption to normal mitotic and meiotic divisions
- negative effects on gene expression and interaction
n.a. Polyploidy. University of Texas at Austin. The Chen Laboratory. 2016. 28 August. 2018
n.a. Speciation. Bioninja. N. p., 2016. Web. 7 Apr. 2016.
Woodhouse, M., Burkart-Waco, D. & Comai, L. Polyploidy. Nature Education 2(1):1. 2009. Web. April 7, 2016.