Study the pedigree chart given below. What does it show?
Correct answer: A. Inheritance of a condition like phenylketonuria as an autosomal recessive trait
- A. Inheritance of a condition like phenylketonuria as an autosomal recessive trait
- B. The pedigree chart is incorrect and does not represent a possible inheritance pattern
- C. Inheritance of a recessive sex-linked disease like haemophilia
- D. Inheritance of a sex-linked inborn error of metabolism like phenylketonuria
Explanation
The correct answer is that the pedigree chart shows the inheritance of a condition like phenylketonuria as an autosomal recessive trait. In such traits, the disorder can skip generations. The condition appears in a homozygous recessive individual (aa) and can manifest in offspring when both parents are carriers (heterozygous Aa), with a 25% chance of the offspring being affected. The other options incorrectly suggest that the chart is wrong or that it represents a sex-linked trait, which does not align with the typical inheritance pattern of autosomal recessive traits.
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About Inheritance
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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