BIOL 2500 - Topic 7 (part 9)

Translocation

When a chromosome breaks and the fragment reattaches to a different chromosome or to a new spot on the same chromosome

Different types of translocation

1.) Translocation heterozygotes

2.) Unbalanced translocation

3.) Reciprocal translocation

4.) Robertsonian translocation

Translocation heterozygotes

Have one WT chromosomes and one altered chromosome

Unbalanced translocation

The fragment reattaches to a new chromosome, with no exchange (one way event)

Reciprocal translocation

Two chromosomes swap fragments with each other (two way event)

Robertsonian translocation

Aka chromosome fusion, when two nonhomologous chromosomes fuse together, with the loss of one of the centromeres

Which of Mendel’s laws still holds true for translocation chromosomes

Law of independent assortment

Different types of segregation for translocated chromosomes

1.) Adjacent-1 segregation

2.) Alternate segregation

Adjacent-1 segregation

It ends up pairing one normal chromosome with a translocated chromosome, resulting in non-viable gametes

Alternate segregation

It pairs up two normal chromosomes in one gamete and two translocated chromosomes in the other, therefore the gametes are viable as the gene dosage is balanced

Robertsonian translocaations in humans

It occurs for chromosomes 13, 14, 15, 20, and 21

P arm of robertsonian translocation

Their p arms generally do not carry essential genes, so loss of the p arm is tolerated

Robertsonian translocation can result in…

Trisomy 21 (by fertilizing normal gametes from one person and n-1 translocated gametes from another)

Why do translocations matter?

1.) It is associated with many types of cancer, as it can interrupt a gene required in cell cycle regulation (such as leukemia)

2.) It leads to genomic instability, due to mutations in DNA repair genes, which can also lead to cancer