Duane I might be the only one but what does tetraploid and aneuploid mean and how do plants be that The Boveri-Sutton chromosome theory
was one of the fundamental steps toward understanding how Mendelian inheritance worked
. Contrary to Douglas Adam's statement in The Hitchhiker's Guide to the Galaxy
and its sequels that 42 is the answer to everything, as far as biology is concerned, the answer is "two".
Mendel's classic experiments with inheritance in peas led to the idea that specific characters were determined by pairs of genes. The textbook example (one of the first thing taught in a course of genetics) is a simple recessive-dominant pair. In humans, a pair of this nature is blue vs. brown eyes, blue being recessive and brown dominant. Research in the century and a half since Mendel conducted his experiments has shown that the picture is generally more complex: few characters are dependent on a simple recessive-dominant pair of genes in such a clear cut way. Indeed, human eye colors aren't just blue and brown, but as an approximation, that's a reasonable place to start.
Thus, a single character is determined by a pair of alleles
. The normal state of most organisms is that genes and the chromosomes which bear them occur in pairs.
Mother Nature loves complexity, and she loves misleading people, so non-two inheritance also occurs, but it is the exception. Humans normally have 23 pairs of chromosomes, or 46 chromosomes in total, but there are aberrant human genomes with more or fewer chromosomes.
The most common deviation is a doubling or even tripling of the entire chromosome complement to give, instead of the usual 2N count, 4N or 6N chromosomes. These are called "polyploids". A doubling to 4N is tetraploid, a tripling to 6N is hexaploid, and so on.Aneuploidy
means that an organism only carries half the usual complement of chromosomes.
In humans, deviations from the usual 2N pattern (N=23) are usually fatal to the fetus, which spontaneously aborts, but some such variations may survive. Down syndrome
is a well known example. Individuals with idiosyncratic variations among the sex chromosomes leading to XXY, XYY, and such sex chromosome makeup are another category that is not always fatal in the womb.
I've written enough: go you to Wikipedia and learn more.