Concepts

A chromosome duplication is a mutation that doubles part of a chromosome. In individuals heterozygous for a chromosome duplication, the duplicated region of the chromosome loops out when homologous chromosomes pair in prophase I of meiosis. Duplications often have major effects on the phenotype, possibly by altering gene dosage.

Wild-type chromosomes

Wild-type chromosomes

Chromosomes do not align properly,.

.resulting in unequal crossing over.

One chromosome has a Bar duplication and the other a deletion.

Chromosomes do not align properly,.

.resulting in unequal crossing over.

One chromosome has a Bar duplication and the other a deletion.

Bar chromosomes

I 9.8 Unequal crossing over produces Bar and double-Bar mutations.

Unequal crossing over between chromosomes containing two copies of Bar.

.produces a chromosome with three Bar copies (double-Bar mutation).

.and a wild-type chromosome.

1 Table 9 1 1

Effects of some chromosome rearrangements in humans

Type of

Rearrangement

Chromosome

Disorder

Symptoms

Duplication

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