Chromosome Alterations. Types of Chromosome. Chromosomes are placed into broad categories depending on the position of the centromere. metacentric : centromere in the middle, with arms of equal length. (A) telocentric : centromere at one end, with only 1 arm. (D)
The suffix -ploidy refers to the number of haploid chromosome sets. Thus, haploid = 1 set, diploid = 2 sets, triploid = 3 sets,etc.
The suffix -somy refers to individual chromosomes. Thus, trisomy = having 3 copies of a chromosome, and monosomy = having 1 copy of a chromosome. Down syndrome, the most common from of mental retardation in humans, is caused by trisomy-21, 3 copies of chromosome 21.
It is far more common to find chromosome number variations in plants than in anmals, since plants can reproduce vegetatively.
Most diploids don’t survive as haploids, because they are usually heterozygous for recessive lethal alleles.
However, all plants have a haploid phase (the gametophyte), and some gametophytes are quite large and complex: mosses, for instance.
Also, male hymenopterans (ants, bees, wasps) are haploid.
It is possible to make a diploid organism that is homozygous at most genes,
repeated matings between close relatives
inducing an unfertilized gamete to undergo mitosis without cell division.
Effects of doubled haploids depends on the species: some organisms survive and are useful in plant breeding, while in other species (such as in humans) is usually lethal.
Heterozygosity helps diploid organisms cope with different environmental conditions.
Triploid grass carp
Autopolyploidy generally results from a failure in meiosis, which gives diploid sperm and egg cells.
To produce autopolyploids, the meiotic spindle can be inhibited with the drug colchicine.
Autopolyploids are often large and healthier that the original diploids. Thus, autopolyploids are commonly found in fruits and vegetables. For instance, commercial chrysanthemums and daylilies are usually tetraploid. Potatoes are also autotetraploids.
47, XYY. Male, usually tall, acne-ridden, and slightly sub-normal in intelligence. Once thought to confer “criminality”, but this has been disproven.
47, XXX. Female, with normal intelligence and only occasional fertility problems. Usually not detected except by accident.