Recall that the Igf2 gene encodes for the growth hormone insulin-like growth factor in mice exhibits genomic imprinting with only the paternal allele being expressed. What is the probability of a mouse pup being dwarf if it is the offspring of a heterozygous dwarf mother (Igf2- Igf2) and a homozygous normal-sized father (Igf2 Igf2)?

The probability of a mouse pup being dwarf if it is the offspring of a heterozygous dwarf mother (Igf2- Igf2) and a wild type normal-sized father (Igf2 Igf2) - 0% chance that all offspring will be wild type due to monoallelic inheritance of the paternal allele

monoallelic inheritance

in this only one gene is expressed either a maternally inherited allele or paternally inherited allele depending on the gene. The genomic imprinting of the Igf2 gene leads to the expression of the paternally inherited copy of the Igf2 gene.

both parents contribute to the gene delivery but only the paternally inherited copy of the Igf2 gene is expressed. The maternally inherited copy of the Igf2 gene is inactive or silent.

The male parent is wild type for the Igf2- allele. Hence, the male parent passes the Igf2- allele to his offspring. Hence, all offspring will exhibit a dwarf phenotype

Parent cross:

Igf2+ Igf2- (heterozygous wildtype female) x Igf2- Igf2- (wild type mutant male)

Gametes of the female parent: Igf2+, Igf2-

Gametes of the male parent: Igf2-

Offspring: Igf2+ Igf2- (dwarf), Igf2- Igf2- (dwarf)

Offspring inherits the Igf2- allele from the male parent. So, all offspring exhibit a dwarf phenotype because only the paternally inherited copy of the Igf2 gene is expressed.

Thus, the probability of offspring being wildtype = 0%

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