Chapter 8: Chromosome Mutations

*Chromosome mutations/aberrations

Variation in chromosome number:

*aneuploidy

*euploidy

*polyploidy

Nondisjunction

Homologous chromosomes: during

anaphase I

Sister chromatids: during anaphase II

Monosomy*Condition in which one member of a chromosome pair is missing (2n-1)

In Drosophila:

Haplo-IV are monosomic for chromosome 4

*develop more slowly, reduced size, impaired viability

In Plants:

Maize, tobacco, evening primrose, Jimson weed

*Segmental deletions

*Cri-du-chat (46,5p-)

Trisomy*Condition in which one chromosome is present in three copies (2n+1)

In Drosophila and humans:

Has severe effects, usually lethal

In Plants:

Jimson weed, rice

Exceptions:

Patau syndrome, 47,13+

Edwards syndrome, 47,18+

Down syndrome, 47,21+

Polyploidy

1) Addition of one or more sets of

chromosomes (replication)

2) Combination of chromosome sets from different species

PolyploidyAutopolyploidy

The benefits of autopolyploid breeding:

increased size of plant organs- roots, leaves, flowers fruits, seeds

Arise in several ways:

*failure of all chromosomes to segregate during meiosis

*two sperm may fertilize an ovum

*experimentation

Allopolyploidy

Polyploidy

Variations in Chromosome StructureDeletions

Variations in Chromosome StructureDuplications

Due to unequal crossing over:

A B C D

A B C D

A B C D

A B C D

A B C D

A B C D

A B C D

A B C D

A B C D

A B C D

A

A

B C D

B C D

Crossover:

Evolution of hemoglobin genes

Variations in Chromosome StructureInversions

*Paracentric

*Pericentric

Variations in Chromosome StructureTranslocation

Variations in Chromosome StructureTranslocation – unbalanced gametes are produced