chapter 7: chromosome mutations

Chapter 7: 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

viabilityIn 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

AllopolyploidyPolyploidy

Variations in Chromosome StructureDeletions

Variations in Chromosome StructureDuplications

Due to unequal crossing over:

A B C D

A B C D

A B C DA B C D

A B C D

A B C D

A B C DA B C D

A B C D

A B C DAA

B C DB 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