Chapter 8 cont One half of the gametes will suffer from such deletions and duplications. The reduction in the number of offspring produced is referred to as semisterility . Whenever an allele assumes a new location in the genome the rate at which transcripts are produced may be affected. This phenomenon is referred to as a position effect. The most common cause of position effects is that an allele that previously existed in a euchromatic region is repositioned near to a heterochromatic region.
Intragenic deletions represent null mutations for that gene.
Often multigenic deletions are lethal due to gene balance. Individuals heterozygous for deletions must form deletion loops to synapse during prophase I of meiosis. Non-deleted regions homologous to deleted regions will be phenotypically expressed whether they are recessive or dominant, so are effectively hemizygous. Recessive alleles in these regions are said to express pseudodominance . Duplications can be located adjacent to each other and called tandem duplications or be separated in the genome and then referred to as insertional duplications .