25 February, 1998
IV.Chromosomal abnormalities and CANCER
cp. Chromosomal mutations, gene
usually gene mutations are not detected by microscopes
N.B. - exceptions:
chromosomes are numbered from the longest to the shortest (more or less - as best as can be determined by light microscopy). This is figure 7.12 from your text (page 272).
position of nucleolar organizers
figure 7_15 (page 277) - in females, one of the X-chromosomes can be inactivated, and can be readily seen as forming a stable heterochromatin throughout the cell cycle.
II. Types of chromosomal Mutations:
figure 7-18 (page 282) Deletions can be mapped by using a testcross.
figure 7.19 Mapping deletions in part of the X-chromosome in polytene salivary gland nuclei of Drosophila melanogaster.
over can cause deletions & duplications
Genetic basis of absent or impaired red-gree colour vision.
figure 7-22 (page 285 in text)
The double-bar mutant in Drosophila is another case of duplication (and
deletion) from unequal crossovers.
figure 7-23 (page 286 in text)
Chromosome inversions can pass through mitosis by forming loops:
figure 7-25 (page 287).
figure 7.30 (page 291) - different possible products from meiosis with
a chromosomal translocation.
Only SOME of the gametes are fertile - this is an example of SEMISTERILITY
figure 7.31a (page 293) - Two sets of chromosomes - one is "normal",
and the other has undergone a translocation.
at Metaphase I in meiosis, the chromosomes line up, and can be
seperated in two different ways.
A ROBERTSONIAN translocation is formed by the fusion of two acrocentric
figure 7.34 (page 295) the mechanism for formation of a Robertsonian
Robertsonian translocations result in the merging (and loss of a small
bit) of chromosomes.
It is likely that human chromosome # 2 came from a translocation between 2 different chromosomes found in chimps.
Deletions can cause many human diseases
Last modified on: 2 February, 2000 by Dave Ussery