Chromosome Number Mutations

1. Aneuploidy:

• Occurs in: Animals and plants.

• Cause: Non-disjunction of chromosomes during meiosis or fertilization.

• Result:

• Mosaic: If aneuploidy occurs in somatic cells during mitosis.

• Mutant: If aneuploidy occurs during the first mitotic division of the zygote.

• Number of aneuploid forms: n (where n is the number of chromosomes that are aneuploid)

2. Polyploidy:

• Occurs in: Mainly in plants.

• Cause: Non-disjunction of all chromosomes during meiosis or fertilization.

• Types:

• Even polyploidy: Having a chromosome number that is an even multiple of the haploid set (2n, 4n, 6n,…).

• Odd polyploidy: Having a chromosome number that is an odd multiple of the haploid set (3n, 5n, 7n,…).

• Applications:

• Seedless fruit production: Using odd polyploidy (e.g., banana, grapes).

• Formation of new species: Through polyploidization.

• Allopolyploidy: When polyploidy occurs between different species.

3. Gene Conversion:

• Occurs in: Prophase I of meiosis (Prophase I).

• Cause: Exchange of segments between homologous chromosomes.

Note:

• Mitosis: Cell division process that produces daughter cells identical to the parent cell.

• Meiosis: Cell division process that produces gametes with half the number of chromosomes as the parent cell.

Conclusion: Chromosome number mutations are an important type of mutation that can cause major changes in phenotype and create new species.