10.1 Chromosomal Rearrangement

Question 1

Deletions

Answer 1

Loss of segment, either internal (two breaks), or terminal (one break). OR arise by unequal crossing over.
Major effect: loss of genetic information.

Question 2

Deletions detection

Answer 2

Can be detected during meiosis; in prophase I the normal chromosome must loop out for the homologous sequences of the chromosomes to align.
Other methods can detect lower heterozygosity or gene dosage.

Question 3

Deletions consequences

Answer 3

Loss of sequences; effect may depend on the size and location. Acentric chromosomes, pseudodominance, haploinsufficiency.

Question 4

Acentric chromosomes

Answer 4

Deletions that span a centromere, most likely lost during cell division. May be lethal.

Question 5

Pseudodominance

Answer 5

Deletions that allow expression of alleles that are normally recessive.

Question 6

Duplications

Answer 6

Repetition of a segment, nothing lost so often little or no effect; usually viable offspring but some excesses or imbalances can cause issues.

Question 7

Duplications origins

Answer 7

Unequal crossing over of misaligned chromosomes during meiosis, (creates a deletion as well).

Question 8

Duplications detection

Answer 8

Duplicated chromosome forms a loop during prophase I. Can also be detected through higher gene dosage.

Question 9

Duplications evolutionary consequences

Answer 9

Both remain the same: redundancy, alter gene dosage
One gene becomes inactive: pseudogenes
One acquires a new function: neofunctionalisation (gene families)

Question 10

Neofunctionalisation

Answer 10

Sources of new genes, creates multigene families such as the globin genes.

Question 11

Duplication gene dosage consequences

Answer 11

May affect phenotype. Amount of protein sythesised is often proportional to the number of gene copies so extra genes : extra proteins.
Eg., Bar region in Drosophila (X), fewer eye facets.

Question 12

Inversions

Answer 12

Two breaks followed by reinsertion in the opposite orientation. Peri or paracentric.

Question 13

Pericentric vs Paracentric

Answer 13

Peri: different sides of the centromere
Para: same side of the centromere

Question 14

Inversion position effects

Answer 14

Change can alter expression, genes in/near chromatin may not be expressed.

Question 15

Inversion suppression of recombination

Answer 15

Within the inverted region - some nonviable gametes and reduced recombination.

Question 16

Crossing over within a paracentric inversion

Answer 16

Formation of inversion loop
Crossing over within inversion
(Dicentric chromatid: bridge breaks as. the two centromeres break apart; acentric chromatid is lost)
Gametes:
- Normal nonrecombinant gamete
- Two nonviable recombinant gametes
- Nonrecombinant gamete with paracentric inversion

Question 17

Crossing over within a pericenttric inversion

Answer 17

Formation of inversion loop
Crossing over within inversion
Gametes:
- Normal nonrecombinanat gamete
- Two nonviable recombinant gametes
- Nonrecombinant gamete with pericentric inversion

Question 18

Translocations

Answer 18

Exchange of segments between nonhomologous chromosomes or different regions of the same chromosome.
Can be reciprocal or not, if no material is lost then it is considered balanced.

Question 19

Reciprocal translocations

Answer 19

Change in gene positions that can alter expression because of association with different proteins, or formation of new gene products.

Question 20

Inversions suppress recombination

Answer 20

Genes within inversion are free to diverge and produce different adaptations.
Eg., Ruff inversion - 3 types of males.