Aneuploidy- chromosomal abnormality (monosomy, trisomy)
Most monosomy are fatal unless it is in the germ cells (sex chromosomes)
● Phenotypic and genetic effects of deletions
○ Homozygosity for deletion is lethal or harmful
■ Depends on size of deletions and affected genes
○ When deletion is deleted from both homologous chromosomes, there are no
copies of genes left, which can be lethal
○ In the case of deletion in heterozygotes, there is only one functional copy of gene
after deletion
■ Can have mutant phenotype due to gene dosage effects
(haploinsufficiency) - to have half of the amount of gene product is not
enough to have phenotypic expression
■ Pseudodominance: when functional copy is deleted, increased risk of
mutation occurs
● Phenotypic and genetic effects of duplications
○ Most duplication have no phenotypic consequences
○ Increased gene copy number of altered expression can cause new phenotypes to
arise
○ Homozygosity or heterozygosity for duplication can be lethal
○ Unequal crossing over between duplicated regions of homologous chromosomes
can result in increased and decreased copy number
○ Tandem duplication: same fragment is repeated in same direction
■ Ex) ABCDE · FG → ABABCDE · FG
● Phenotypic effects of inversions
○ Inversion switches location of gene so will affect position
○ Most inversions do not result in abnormal phenotype
○ Abnormal phenotype can occur if
■ Inversion disrupts gene
■ Inversions places gene near regulatory sequences for other genes or near
heterochromatin
○ Paracentric inversion: near centromere
■ EX) ABCDE · FG → AEDCG · FG
○ Pericentric inversion: includes centromere when positions are switched
■ Ex) ABCDE · FG → AF · EDCBG
● Sex Chromosome Aneuploidy
○ Sex chromosome aneuploidy is tolerated because X inactivation occurs but they
do feel symptoms because they have pseudoautosomal (PAR) genes where they
synapse with Y chromosome and these genes are crucial for normal embryonic
development.
Most monosomy are fatal unless it is in the germ cells (sex chromosomes)
● Phenotypic and genetic effects of deletions
○ Homozygosity for deletion is lethal or harmful
■ Depends on size of deletions and affected genes
○ When deletion is deleted from both homologous chromosomes, there are no
copies of genes left, which can be lethal
○ In the case of deletion in heterozygotes, there is only one functional copy of gene
after deletion
■ Can have mutant phenotype due to gene dosage effects
(haploinsufficiency) - to have half of the amount of gene product is not
enough to have phenotypic expression
■ Pseudodominance: when functional copy is deleted, increased risk of
mutation occurs
● Phenotypic and genetic effects of duplications
○ Most duplication have no phenotypic consequences
○ Increased gene copy number of altered expression can cause new phenotypes to
arise
○ Homozygosity or heterozygosity for duplication can be lethal
○ Unequal crossing over between duplicated regions of homologous chromosomes
can result in increased and decreased copy number
○ Tandem duplication: same fragment is repeated in same direction
■ Ex) ABCDE · FG → ABABCDE · FG
● Phenotypic effects of inversions
○ Inversion switches location of gene so will affect position
○ Most inversions do not result in abnormal phenotype
○ Abnormal phenotype can occur if
■ Inversion disrupts gene
■ Inversions places gene near regulatory sequences for other genes or near
heterochromatin
○ Paracentric inversion: near centromere
■ EX) ABCDE · FG → AEDCG · FG
○ Pericentric inversion: includes centromere when positions are switched
■ Ex) ABCDE · FG → AF · EDCBG
● Sex Chromosome Aneuploidy
○ Sex chromosome aneuploidy is tolerated because X inactivation occurs but they
do feel symptoms because they have pseudoautosomal (PAR) genes where they
synapse with Y chromosome and these genes are crucial for normal embryonic
development.
