A couple has 6 daughters. What is the probability of their next baby being a girl?
Correct answer: D. 50%
- A. 100%
- B. 10%
- C. 16.6%
- D. 50%
Explanation
The ratio of the probability of the birth of a son to that of a daughter is always 1:1, regardless of the gender of the older children. This is because during fertilization of an ovum by a sperm there are only two possibilities; either a sperm carrying an X chromosome fertilizes an egg with an X chromosome to get the XX genotype, which is for females, or a sperm carrying a Y chromosome fertilizes an egg with X chromosome to get XY genotype, which is for male. This is not affected by the gender of any children the couple may have had before. Hence, the correct option is 50%.
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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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