Genomic imprinting
2nd main explanation for non-traditional inheritance (doesn’t fit expectations of Mendelian inheritance)
Genomic imprinting
• The process of gametogenesis in one sex marks some genetic material as being different from its
counterpart supplied by the opposite sex
• Imprinting suppresses action of the imprinted allele, so trait is suppressed – imprinted allele is not
expressed
• Early evidence of imprinting
o Mouse embryos
▪ Can use nuclear transplantation so both haploid chromosome complements in
embryo derived from same parent
▪ Embryos with maternally derived nucleus have poorly developed extra-embryonic
membranes, although embryos are normal
▪ Embryos with paternally derived nucleus have normal membranes but abnormal
embryos
▪ Both are non-viable for life – shoes important need for both paternal and maternal
pronucleus for normal development
▪ Imprinting during gametogenesis possible explanation
o Triploids
▪ Diandric triploids (2 male, 1 female genome) have large, abnormal placenta
▪ Digynic triploids (2 female, 1 male genome) have underdeveloped placentas but can
survive long enough to be studied
o Uniparental disomy (UPD) –
▪ Euploid (normal) genomes where both copies of one chromosome, or major portion
of chromosome, from each parent
▪ Believed to arise from non-disjunction in both parents (failure to separate at
anaphase)
▪ Gives rise to 2 copies of a chromosome in a gamete from one parent and no copies
of the chromosome from the other parent
▪ Can arise from translocation, where major parts of both chromosome derived from
same parent
▪ UPD from balanced translocations (in mice) helped to define which regions of
genome are susceptible to imprinting
▪ Types of UPD
Types of genomic imprinting
• Maternal imprinting – allele is NOT expressed when transmitted by mother (is expressed when
transmitted by father)
2nd main explanation for non-traditional inheritance (doesn’t fit expectations of Mendelian inheritance)
Genomic imprinting
• The process of gametogenesis in one sex marks some genetic material as being different from its
counterpart supplied by the opposite sex
• Imprinting suppresses action of the imprinted allele, so trait is suppressed – imprinted allele is not
expressed
• Early evidence of imprinting
o Mouse embryos
▪ Can use nuclear transplantation so both haploid chromosome complements in
embryo derived from same parent
▪ Embryos with maternally derived nucleus have poorly developed extra-embryonic
membranes, although embryos are normal
▪ Embryos with paternally derived nucleus have normal membranes but abnormal
embryos
▪ Both are non-viable for life – shoes important need for both paternal and maternal
pronucleus for normal development
▪ Imprinting during gametogenesis possible explanation
o Triploids
▪ Diandric triploids (2 male, 1 female genome) have large, abnormal placenta
▪ Digynic triploids (2 female, 1 male genome) have underdeveloped placentas but can
survive long enough to be studied
o Uniparental disomy (UPD) –
▪ Euploid (normal) genomes where both copies of one chromosome, or major portion
of chromosome, from each parent
▪ Believed to arise from non-disjunction in both parents (failure to separate at
anaphase)
▪ Gives rise to 2 copies of a chromosome in a gamete from one parent and no copies
of the chromosome from the other parent
▪ Can arise from translocation, where major parts of both chromosome derived from
same parent
▪ UPD from balanced translocations (in mice) helped to define which regions of
genome are susceptible to imprinting
▪ Types of UPD
Types of genomic imprinting
• Maternal imprinting – allele is NOT expressed when transmitted by mother (is expressed when
transmitted by father)
