Changes in Chromosome Structure Flashcards
In what case can an abnormal chromosome survive meiosis and mitosis?
If the has one centromere and two telomeres.
What are balanced rearrangements?
There is no gain or loss of genetic material, chromosome complement is complete.
When may balanced rearrangements cause harm?
The breakpoint disrupts vital gene.
Heterozygotes are at risk of producing unbalanced gametes.
What are unbalanced chromosome rearrangements?
There is loss or gain of genetic material.
What is a chromosome deletion?
Loss of part of a chromosomes resulting in effective monosomy for that segment.
Why do chromosome deletions result in defects?
Haplo- insufficiency.
Deletions in greater than __% of the total haploid genome are lethal.
2%
What is Cri-du-chat syndrome?
Deletion of the short arm of chromosome 5.
What is Wolf-Hirschhorn syndrome?
Visible deletions of the tip of chromosome 4.
What is WAGR (Wilm’s tumour, Aniridia, Genitourinary abnormalities and Retardation of growth and development) syndrome?
Deletion of the region of 11p13
What are duplications most commonly caused by?
Abnormal crossing over if chromosomes mis-pair due to the presence of repeated sequences in the genome. Can occur between sister and non-sister chromosomes.
Are all duplications harmful?
If low gene dosage is duplicated, then the duplication is not harmful.
What are the three evolutionary outcomes of duplications?
The two copies stay similar, one copy degrades if it is not needed or the new copy acquires a new function (gene families).
What are inversions?
Two breaks occur in a chromosome, the internal region rotates 180 degrees and the broken ends ‘heal’.
What is a pericentric inversion?
The inversion incorporates the centromere.
What is a paracentric inversion?
The inversion does not incorporate the centromere.
When may inversions be harmful?
A break may result in gene disruption.
A heterozygotes risks producing unbalanced gametes.
What are inversion loops?
A loop forms in a heterozygotes so that a chromosome with an inversion can line up with a normal chromosome.
In which cases of crossover in a heterozygote for pericentric inversions produce unbalanced gametes?
If crossover occurs in the inverted region.
The larger the inversion the more/less likely crossovers will occur, increasing/decreasing the chance of unbalanced gametes.
The larger the inversion the more likely crossovers will occur, increasing the chance of unbalanced gametes.
What are acentric chromosomes and what happens to them?
Chromosomes with no centromere. Spindle fibres cannot attach and the chromosome is lost.
What are dicentric chromosomes?
Chromosomes with two centromeres. A dicentric bridge forms during meiosis so that when the chromosomes separate, it will break. This causes deletion. Meiosis progression is usually blocked.
What are some evolutionary advantages of inversions?
Groups of alleles are held together as recombination is suppressed in heterozygotes. This produced haplotype may confer survival advantage.
