ceptimus
08-14-2007, 10:23 PM
Eggs and sperm, which contain one set of chromosomes each, are haploid. Human eggs and sperm contain 23 chromosomes each and so have a haploid number of 23.
Most cells in the human body (and other animal bodies) are diploid, containing one set of chromosomes from the mother and one from the father, so humans have a diploid number of 46 (goats have a diploid number of 60 and hermit crabs have a diploid number of 254).
I won't bold the ploid anymore - I've made the point, but there are lots of ploids to come...
Plants, unlike most animals, are more cavalier with their chromosomes...
It is common in plants for each cell to have four sets of chromosomes (tetraploid): presumably at some time in history, the chromosomes of a plant cell divided in the normal way (in preparation for cell division) but the cell then failed to divide. The resulting tetraploid plants cannot interbreed with their diploid parents, but they can interbreed with other similar tetraploid plants of their own kind, forming an instant new species. For example, the common potato that we eat is a tetraploid derivative of the diploid wild potatoes of South America.
It doesn't stop there - the tetraploid plants sometimes double their chromosomes again to become octoploid, and so on - the general term is polyploid. Ferns such as Ophioglossum have as many as 768 chromosomes.
With all these copies of chromosomes flying around, it's no surprise that sometimes a plant will end up losing a few. Some of the resulting organisms are quite viable, even vigourous. Sugar Cane has an anomalous number of chromosomes and is an example of an aneuploid organism.
The cultivated banana is an oddity - it is triploid. At some time in the past, a tetraploid ancestor of the banana must have 'mated' with a diploid ancestor. The banana has two sets of chromosomes from its tetraploid ancestor and one set from its diploid ancestor. The banana is sterile, its fruits containing no seeds - so banana plants have to be produced by taking cuttings from other banana plants - they are all effectively clones of the same plant.
The cultivated banana is analogous with a mule - a mule is the offspring of a male donkey and a female horse. Although mules are strong and useful animals, they are sterile. However, a mules is not triploid as both its parents are the normal (for animals) diploid.
(a lot of the above is paraphrased from The Secret Life of Trees - How They Live and Why They Matter by Colin Tudge. I recommend the book)
Most cells in the human body (and other animal bodies) are diploid, containing one set of chromosomes from the mother and one from the father, so humans have a diploid number of 46 (goats have a diploid number of 60 and hermit crabs have a diploid number of 254).
I won't bold the ploid anymore - I've made the point, but there are lots of ploids to come...
Plants, unlike most animals, are more cavalier with their chromosomes...
It is common in plants for each cell to have four sets of chromosomes (tetraploid): presumably at some time in history, the chromosomes of a plant cell divided in the normal way (in preparation for cell division) but the cell then failed to divide. The resulting tetraploid plants cannot interbreed with their diploid parents, but they can interbreed with other similar tetraploid plants of their own kind, forming an instant new species. For example, the common potato that we eat is a tetraploid derivative of the diploid wild potatoes of South America.
It doesn't stop there - the tetraploid plants sometimes double their chromosomes again to become octoploid, and so on - the general term is polyploid. Ferns such as Ophioglossum have as many as 768 chromosomes.
With all these copies of chromosomes flying around, it's no surprise that sometimes a plant will end up losing a few. Some of the resulting organisms are quite viable, even vigourous. Sugar Cane has an anomalous number of chromosomes and is an example of an aneuploid organism.
The cultivated banana is an oddity - it is triploid. At some time in the past, a tetraploid ancestor of the banana must have 'mated' with a diploid ancestor. The banana has two sets of chromosomes from its tetraploid ancestor and one set from its diploid ancestor. The banana is sterile, its fruits containing no seeds - so banana plants have to be produced by taking cuttings from other banana plants - they are all effectively clones of the same plant.
The cultivated banana is analogous with a mule - a mule is the offspring of a male donkey and a female horse. Although mules are strong and useful animals, they are sterile. However, a mules is not triploid as both its parents are the normal (for animals) diploid.
(a lot of the above is paraphrased from The Secret Life of Trees - How They Live and Why They Matter by Colin Tudge. I recommend the book)