A mother and father both have normal karyotypes. The father is color blind, but the mother is
not. Color blindness is determined by a recessive mutation on the X chromosome. Their first
child is a color-blind girl with an XX karyotype. The family consults a genetic counselor because
their second child is a color blind boy with Klinefelter\'s syndrome. Klinefelter\'s syndrome
results when a child has the sex chromosome constitution XXY. Which of the following
statements is true about the nondisjunction event that led to the boy with Klinefelter\'s syndrome
(assume no recombination)? Only during the first meiotic division in Dad. Only during the
second meiotic division in Dad. Only during the first meiotic division in Mom. Only during the
second meiotic division in Mom. Either a or d. Either a orb.
Solution
ans-e
Non-disjunction (failure of homologous chromosomes) at paternal meiosis I produces XY
secondary spermatocytes and a 24,XY gamete. Fertilization with a 23,X ovum produce a
47,XXY individual (Klinefelter syndrome). Only nondisjunction at paternal meiosis II produces
a 24,YY gamete that yields a 47,XYY individual after fertilization..
A mother and father both have normal karyotypes. The father is color .pdf
1. A mother and father both have normal karyotypes. The father is color blind, but the mother is
not. Color blindness is determined by a recessive mutation on the X chromosome. Their first
child is a color-blind girl with an XX karyotype. The family consults a genetic counselor because
their second child is a color-blind boy with Klinefelter's syndrome. Klinefelter's syndrome
results when a child has the sex chromosome constitution XXY. Which of the following
statements is true about the nondisjunction event that led to the boy with Klinefelter's syndrome
(assume no recombination)? Only during the first meiotic division in Dad. Only during the
second meiotic division in Dad. Only during the first meiotic division in Mom. Only during the
second meiotic division in Mom. Either a or d. Either a orb.
Solution
ans-e
Non-disjunction (failure of homologous chromosomes) at paternal meiosis I produces XY
secondary spermatocytes and a 24,XY gamete. Fertilization with a 23,X ovum produce a
47,XXY individual (Klinefelter syndrome). Only nondisjunction at paternal meiosis II produces
a 24,YY gamete that yields a 47,XYY individual after fertilization.
