Changes in Chromosome Structure

Question 1

In what case can an abnormal chromosome survive meiosis and mitosis?

Answer 1

If the has one centromere and two telomeres.

Question 2

What are balanced rearrangements?

Answer 2

There is no gain or loss of genetic material, chromosome complement is complete.

Question 3

When may balanced rearrangements cause harm?

Answer 3

The breakpoint disrupts vital gene.

Heterozygotes are at risk of producing unbalanced gametes.

Question 4

What are unbalanced chromosome rearrangements?

Answer 4

There is loss or gain of genetic material.

Question 5

What is a chromosome deletion?

Answer 5

Loss of part of a chromosomes resulting in effective monosomy for that segment.

Question 6

Why do chromosome deletions result in defects?

Answer 6

Haplo- insufficiency.

Question 7

Deletions in greater than __% of the total haploid genome are lethal.

Answer 7

2%

Question 8

What is Cri-du-chat syndrome?

Answer 8

Deletion of the short arm of chromosome 5.

Question 9

What is Wolf-Hirschhorn syndrome?

Answer 9

Visible deletions of the tip of chromosome 4.

Question 10

What is WAGR (Wilm’s tumour, Aniridia, Genitourinary abnormalities and Retardation of growth and development) syndrome?

Answer 10

Deletion of the region of 11p13

Question 11

What are duplications most commonly caused by?

Answer 11

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.

Question 12

Are all duplications harmful?

Answer 12

If low gene dosage is duplicated, then the duplication is not harmful.

Question 13

What are the three evolutionary outcomes of duplications?

Answer 13

The two copies stay similar, one copy degrades if it is not needed or the new copy acquires a new function (gene families).

Question 14

What are inversions?

Answer 14

Two breaks occur in a chromosome, the internal region rotates 180 degrees and the broken ends ‘heal’.

Question 15

What is a pericentric inversion?

Answer 15

The inversion incorporates the centromere.

Question 16

What is a paracentric inversion?

Answer 16

The inversion does not incorporate the centromere.

Question 17

When may inversions be harmful?

Answer 17

A break may result in gene disruption.

A heterozygotes risks producing unbalanced gametes.

Question 18

What are inversion loops?

Answer 18

A loop forms in a heterozygotes so that a chromosome with an inversion can line up with a normal chromosome.

Question 19

In which cases of crossover in a heterozygote for pericentric inversions produce unbalanced gametes?

Answer 19

If crossover occurs in the inverted region.

Question 20

The larger the inversion the more/less likely crossovers will occur, increasing/decreasing the chance of unbalanced gametes.

Answer 20

The larger the inversion the more likely crossovers will occur, increasing the chance of unbalanced gametes.

Question 21

What are acentric chromosomes and what happens to them?

Answer 21

Chromosomes with no centromere. Spindle fibres cannot attach and the chromosome is lost.

Question 22

What are dicentric chromosomes?

Answer 22

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.

Question 23

What are some evolutionary advantages of inversions?

Answer 23

Groups of alleles are held together as recombination is suppressed in heterozygotes. This produced haplotype may confer survival advantage.