Lecture 13a Flashcards
(25 cards)
What is a chromosome mutation?
Changes in a chromosome region encompassing multiple genes
What are euploid organisms?
Organism with the normal number chromosome sets.
What is an aberrant euploid?
Organism that has more or fewer than the normal number of sets.
What is polyploidy?
Organisms that have more than two chromosome sets. It is better tolerated than aneuploidy and is common among plants. Polyploids tend to be proportionally bigger.
Ex. triploid (3n), tetraploid (4n), etc.
What is monoploid?
A haploid set in a diploid species
What are autopolyploids?
Multiple chromosome sets originating from within one species
What are allopolyploids?
Chromosome sets from two or more different species (form only between closely related species)
What is aneuploidy?
Extra/missing chromosomes from a full set.
What does it mean to be trisomic? monosomic? nullisomic?
Trisomic: 1 extra copy of 1 chromosome in a diploid (2n+1)
Monosomic: 1 fewer copy of 1 chromosome in a diploid (2n-1)
Nullisomic: 2n-2
When is a polyploidy organism stable vs unstable?
Stable (fertile): ploidy is even
Unstable: ploidy is odd –> messes up lining up of homologs in Meiosis 1 (gametes and offspring are aneuploid)
What are autotetraploids?
Arise by the doubling of a 2n to 4n. Can have regular meiosis if chromosomes pair as two bivalents or one quadrivalent. Nonfunctional aneuploid gametes form if a trivalent + univalent occur.
How do polyploids arise?
1) Natural accident: Ex. 2n gamete + n gamete = 3n offspring or 2n gamete + 2n gamete = 4n offspring
2) Colchicine treatment: prevents microtubule formation in mitosis –> doubled chromosome complement in cells
What is allopolyploidy?
Combining chromosomes from gametes of two species. The species must be closely related. Possibility of being sterile if the chromosomes are not homologous enough to properly segregate in meiosis
What is amphiploidy?
First allo then auto. Organism has a diploid set of chromosomes from each parent.
What is aneuploidy?
Chromosome number is different than the WT number.. Mostly due to nondisjunction in M1 or M2. Nondisjunction causes the gamete to be n+1 or n-1. Then, the consequence is felt in offspring when aberrant gamete combines w/ normal gamete to make 2n+1 or 2n-1 offspring.
What is nondisjunction?
Failure of normal segregation of homologous chromosomes or chromatids to opposite poles at meiotic or mitotic divisions.
What does nondisjunction at M1 lead to?
n+1
n+1
n-1
n-1
What does nondisjunction at M2 lead to?
n+1
n-1
n
n
Why is nondisjunction bad?
1) missing a copy of a chromosome means missing those chromosomes genes –> less mRNA –> less protein
2) Recessive alleles on other chromosome copy take full effect
3) Extra copies of a chromosome –> more protein –> can screw up rxn balance in cell
4) Most trisomes lead to miscarriage
What are the 4 types of chromosomal rearrangements?
Deletion, Deletion&Duplication, Inversion, Translocation
What are the two ways in which chromosomal rearrangements arise?
1) Breakage and rejoining
2) Crossing over between repetitive DNA
What is deletion?
A chromosome segment is lost. Breakage in DNA can be caused by X ray or gamma rays. Crossing over occurs on same chromosome (loop forms).
What is deletion & duplication?
Generally occurs because of unequal crossing over between homologous chromosomes. One chromosome has parts deleted and the other chromosome has those parts added on to it. Severity depends on gene function and length of deletion/duplication. It creates partial aneuploidy.
What is inversion?
The orientation of a segment on a chromosome is reversed. Usually has no effect but if breakage occurs in the middle of a gene then effect is negative.
