A girl has blood group A and her brother has blood group B. Which combination of genotypes cannot belong to their parents:
Correct answer: D. Option D: Both parents have genotype 'OO'
- A. Option A: Both parents have genotype 'AO'
- B. Option B: Both parents have genotype 'BO'
- C. Option C: Both parents have genotype 'AB'
- D. Option D: Both parents have genotype 'OO'
Explanation
Parents with the genotype 'OO' can only have children with blood group O, as the 'O' allele is recessive. For a child to have blood group A, B, or AB, one of the parents must have an 'A' or 'B' allele. Thus, Option D is the correct answer because parents with 'OO' genotype cannot have children with blood groups A or B.Options A, B, and C involve combinations where the parents have alleles 'A', 'B', or 'AB', which can produce the observed blood groups in the children. Therefore, these options are possible parental genotypes, unlike Option D.
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Mendel's laws explain segregation, independent assortment and the prediction of genetic ratios using alleles, genotypes and phenotypes. The chapter also covers linked genes, recombination and crossing over during meiosis, then applies pedigree reasoning to X-linked recessive traits, which show different inheritance patterns in males and females.
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