BIOL 2500 - Topic 7 (part 2)

Chromosomal mutations

Large-scale changes in chromosomes, different from DNA/point mutations

Chromosomal mutations vs. point mutations

Chromosomal mutations are much larger than point mutations as it affects multiple genes, not just one, resulting in major phenotypic changes, as it causes changes in chromosome numbers and/or structure

Detection of chromosomal mutations

It can be detected under a microscope by seeing differences in the banding pattern (which you cannot do with point mutations)

Two types of changes in chromosome numbers

1.) Aberrant euploidy —> changes in whole chromosomal sets (2N —> 4N)

2.) Aneuploidy —> Changes in parts of chromosomal sets (Loss or gain of a chromosome #2)

Euploids

Organisms with multiple of the basic chromosome set, such as diploid, triploid, etc

Normal euploid

Diploid (normal number of sets)

Aberrant euploid

Organisms that have more or less than the regular euploid number (i.e. ants, wasps, strawberries, etc)

Abberant euploids examples

1.) Monoploid

2.) Triploid (3n)

3.) Tetraploid (4n)

Monoploid vs. haploid

Haploid refers to organisms that usually only have one set of chromosomes, whereas monoploids refer to organisms that usually have 2 sets of chromosomes but only have one

Polyploidy

Organisms with more than 2 chromosomal sets

Origin of polyploidy

Some can be a result of aberrant euploidy, but some are just naturally polyploid, such as most plants

The more the chromosomal sets, the ______ the organism

Bigger

Even vs. odd sets of chromosomes

Even chromosomal sets are much more common than odd sets, as whole genomes usually double and redouble

Autopolyploidy

Polyploidy where the chromosomes are derived from a single species

Allopolyploidy

Polyploidy where the chromosomes are derived from multiple species

How triploids arise

They are usually autopolyploid, by spontaneous nondisjunction

Pairing of triploids

1.) Because there are uneven numbers of chromosomes, triploids cannot pair during meiosis

2.) Therefore, the bivalents separate as expected, but univariants randomly go to either pole

Resulting number of chromosomes in gametes in triploids

1.) One gamete has 2 chromosomes (n+1)

2.) The other has 1 chromosome (n)