Class Notes (808,753)
Canada (493,377)
Biology (Sci) (2,417)
BIOL 202 (224)

10. Large Scale Chromosomal Changes in Plants.pdf

5 Pages
Unlock Document

McGill University
Biology (Sci)
BIOL 202
Tamara Western

Large Scale Chromosomal Changes in Plants: As we know DNA is not naked in the cell; genes are part of a bigger genome, which is wrapped up into a chromosome  Any modification in the shape and/or number of chromosomes in a cell will have drastic effects  A chromosome is essentially shaped like an X, the center being the centromere o Two short arms on the same side of the chromosomes are the p arms (petit arms) and the two longer arms are known as the q arms (because q comes after p) Visualizing chromosomes can be done most easily by taking a blood sample, centrifuging it, and isolating the WBCs, which are the only blood cells with nuclei  They are placed on a petri dish and left to divide in culture; cell division is stopped with certain drugs by disabling the mitotic spindle  A hypotonic solution is then used to swell the cells up, at which point they are squished onto a slide and stained using a fluorescent or radioactive dye/probe (e.g. biotin, which we have seen before)  Stopping the cells in division is necessary because in the cell’s cycle, only 1/24 of it is spent in mitosis Similarly as with the size of the genomes, the number of chromosomes pairs in various organisms is NOT indicative of its complexity  For example, we have roughly the same number of chromosomes as wheat and potatoes, while dogs have almost double the number of chromosomes and carps have over twice as many Of course, we also need to have the right number of chromosomes in the cell; the number of chromosomes is known as the ploidy  A euploid is a complete, normal set of chromosomes, e.g. 46 in humans (23 pairs)  An aneuploid is when the chromosomes are over or under represented o E.g. trisomy, having 3 chromosomes instead of two, is a case of over representation and leads to genetic imbalance and phenotypic changes  Polyploids are an extra set of chromosomes, commonly found in plants  Diploids are organisms with two sets of each chromosomes, i.e. humans and mammals  Tetraploids are organisms with 4 sets of chromosomes  Rearrangements produce abnormal chromosomes o These can be deletion, translocations, and duplication, all of whicih have drastic effects  These are NOT point mutations, we are talking about mutations on the chromosomal of level The following table shows a list of ploidy in various normal and abnormal cases  Euploids can either be mono, di, tri, or tetraploids, all of which exist in this state normally o Male bees, wasps, ants and mammals are diploids o Plants commonly show tri and tetraploidy  Aneuploids in humans can either have 1 or 3 chromosomes o Monosomic people only have 1 chromosome copy of ONE chromosome (not all of them, that would make the monoploid) o Trisomic people have an extra copy of ONE chromosome (not all, that would make them triploids)  In humans, it is not possible to be mono/trisomic for all our chromosomes, normally it’s just one Polyploidy is very common in plants but rarer in animals  Autopolyploids have multiple chromosome sets from within one species, usually triploids  Allopolyploids have multiple chromosomes sets from different species o Through evolution, this is how species are generated Sterility is a common problem in triploids because of unequal pairing during meiosis  There are two pathways which meiosis pairing can take; either will result in most cells being sterile o Segregation like a bivalent and univalent, or like a trivalent Tetraploids can also be sterile in some cases, although the chances of having fertile gametes is higher than for triploids  The tetraploid can segregate like two bivalents which will produce fertile gametes  Segregation as one quadravalent can sometimes be fertile, but other times will be sterile depending on arrangement  Segregation as a trivalent and a univalent will produce sterile gametes  Most tetraploid plants will produce sterile gametes, but some plants, like bread wheat and raphanobrassica, though being tetraploid, are still fertile; why? o Diploid radishes (raphnus) which are 2n = 18 were crossed with cabbage (brassica) which are also 2n = 18, but all the F1 were sterile because the chromosomes couldn’t pair because they weren’t the same o However, in some of the progeny, natu
More Less

Related notes for BIOL 202

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.