A maternal effect gene exist in dominant A (normal) allele and recessive a (abnormal) allele. What would be the ratios of genotypes and phenotypes for the offspring of the following crosses?
a. aa female × AA male
b. AA female × aa male
c. Aa female × Aa male
a. All offspring will be Aa (heterozygous) genotype and normal phenotype (since they inherit a dominant A allele from the father and a recessive a allele from the mother, but the maternal effect gene will override the abnormal phenotype from the recessive allele).
b. All offspring will be Aa (heterozygous) genotype and normal phenotype (since they inherit a dominant A allele from the mother and a recessive a allele from the father, but the maternal effect gene will override the abnormal phenotype from the recessive allele).
c. The genotypic ratio will be 1:2:1 (AA:Aa:aa). The phenotypic ratio will be 3 normal : 1 abnormal. This is because among the 4 possible offspring genotypes, only the aa genotype will display the abnormal phenotype since the maternal effect gene is only present in the mother's egg. The Aa genotype will be normal due to the dominant A allele inherited from one parent, and the AA genotype will obviously be normal since both alleles are dominant.