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Modern Genetic Analysis
8. Chromosome Mutations
Key Concepts
In organisms with multiple chromosome sets (polyploids), an even number of sets is more likely to result in fertility than is an odd number of sets.
Crosses between two different species followed by the doubling of the chromosome number in the hybrid produces a special kind of fertile inter-specific polyploid.
Variants differing from wild type by parts of chromosome sets show phenotypic abnormalities caused by an upset gene balance.
Variants in which a single chromosome has been gained or lost generally arise by abnormal chromosome segregation at meiosis.
Owing to the strong meiotic pairing affinity of homologous chromosomes, diploids with one standard chromosome set and one rearranged set produce meiotic pairing structures that have shapes and properties unique to that rearrangement.
A deletion in one chromosome set is generally deleterious as a result of gene imbalance and the unmasking of deleterious alleles in the other chromosome set.
Duplications can lead to gene imbalance, but they can also provide extra material for evolutionary divergence.
Heterozygous inversions result in reduced recombination between genes spanning the inversion and in reduced fertility.
A heterozygous translocation results in 50 percent sterility and linkage of genes on the translocated chromosomes in the translocation.

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