bsci 222 topic 9

Duplication

Chromosomal rearrangement in which part of the chromosome has been doubled which result in cnvs and paralogous genes.

Tandem duplication

Right next to each other

Dispersed duplication

Not right next to each other

Cnvs

Inherited or somatic mutations, copies are very similar, may affect phenotype

Paralogous genes

Homologous in 1 species that arise from duplication followed by point mutation to change function

Deletion

Loss of a chromosome segment resulting in pseudominance (exposes recessive alleles in heterozygoyes) and cnvs

Inversion

Chromosome segment reversed (flipped 180 degrees)

paracentric inversion

Inversion falls outside the centromere (in p arm and q arm only)

Pericentric inversion

Inversion includes centromere

Paracentric consequence

formation of dicentric bridge, resulting in huge chromosomal deletions in recombinant gametes

Pericentric consequences

Uneven information exchange, resulting in duplications and deletions in recombinant gametes

Translocation

Movement of part of one chromosome to a non homologous chromosome. Can be reciprocal or non reciprocal

Robertsonian translocation

Reciprocal translocation at near centromeres of two Acrocentric (long an arm and very short p arm) chromosomes

How do chromosomal rearrangements arise

1. Chromosomal breaks induce rearrangements when repaired

2. Unequal crossing over

3. Transposable elements

Transposable elements

Sequences that are dispersed throughout the genome, many or few copies, may be expressed, two categories are dna based and rna based

DNA transposing (left)

Moves Original copy (Cut and paste action.) Proliferation by transpose enzyme into other parts of genome

Retrotransposons (right)

Duplicates and moves new copy (copy and paste) Proliferation by reverse transcription of RNA product.

Rearrangement affecting gene expression and phenotype in balanced rearrangement

1 changing level of gene expression

2 gene dosage

3 position effect

4 new linkage relationship

5 interrupt the gene sequence

Synteny

The conservation of the order of genes on chromosomes between related genes

Autopolyplodiy

Multiples of one species, haploid sets (2N) triploids (3N) tetraploids (4N)

Allopolyploidy

Multiples of different species haploid sets. May be 2N or more (3N, 4N)

What determines fertility in allopolyploids

1. matching haploid numbers in vertebrates

2. Infertility may be the result of chromosomal rearrangements or point mutations in critical genes