BIOL 2500 - Topic 7 (part 6)

Rearrangements

Changes to chromosome structure that can result in the loss or addition of genes

Effect of rearrangements

It causes gene dosage imbalances, which can greatly affect animals

Chromosomal ___________ are very common

Duplications

Significance of chromosomal duplications

It is how we get novel genes (such as hemoglobin)

Importance of chromosomal reaarangements

1.) Source of genetic variation (can even cause speciation)

2.) A major cause of genetic disorders and conditions

3.) It can cause infertility

4 kinds of rearrengments

1.) Deletions

2.) Duplications

3.) Inversions

4.) Translocations

Cause of rearrangements

1.) Chromosome breakage

2.) Unequal crossing over

Causes of chromosome breakage

1.) Double-stranded breaks during DNA synthesis

2.) Mutagens (chemicals, radiation, etc)

3.) Transposons

4.) Recombination error

Recombination error that causes rearrangement

It is when the chiasma fails to disconnect, which puts a strain on the chromosome

What happens when the chromosomes break

1.) Segments of the chromosomes can be lost

2.) It results in sticky ends that can rejoin to the chromosome or another in a new cofiguration

Unequal crossing over

When chromosomes do not align properly, due to the presence of repetitive DNA sequences, resulting in non allelic homologous recombination

Non-allelic homologous recombination (NAHR)

It is when the DNA sequences on one chromosome do not align at the same spot on the second homolog

Viable chromosomes

Regardless of how rearrangement occurs, only chromosomes that have one centromere and 2 telomeres are viable

Acentric chromosomes

They lack a centromere (therefore chromosome is completely lost)

Dicentric chromosomes

It has two centromeres, but it is still not viable because it forms an anaphase bridge, which causes the chromosome to break into two, but one of their ends would not have a telomere region

Two types of rearrangements

1.) Unbalanced (deletions and duplications), cause a change in gene dosage

2.) Balanced (inversions and translocations), it changes the gene order but gene dosage remains the same

Do balanced rearrangements affect the phenotype

It depends on whether gene order matters in the inverted/translocated region