[ 321 ] Life Science GED ® TEST SCIENCE FLASH REVIEW • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • Refer to the following passage to answer the next five questions. Hemophilia is a rare bleeding disorder in which the blood does not clot normally. People born with hemophilia have little or no clotting factor, the protein needed for normal blood clotting. It is usually inherited, meaning that the disorder is passed from parents to their offspring through genes. Hemophilia in humans is due to a mutation in a gene found on the X chromosome. Mothers always contribute an X chromosome to their offspring while fathers contribute either an X or a Y chromosome. If hemophilia is found on any of these X chromosomes, it can be passed on to the offspring. A carrier of hemophilia is a female with one normal X chromosome and one X chromosome carrying the mutation. A male cannot be a carrier because his genetic makeup is XY; thus, the presence of the mutation would result in the disease. The chart shown here is a Punnett square that shows the probability of a normal male and a carrier female producing an offspring with hemophilia. X Y Key XX XY X X X Y Normal XY Male X Normal XX Female Female X X Carrier X Male With X Y Hemophilia Which piece of evidence from the passage best supports the statement that an affected male will never transmit the hemophilia gene to his sons? A. Hemophilia in humans is due to mutation in a gene found on the X chromosome. B. Mothers always contribute an X chromosome to their offspring while fathers contribute either an X or a Y chromosome. C. A carrier of hemophilia is a female with one normal X chromosome and an X chromosome carrying the mutation. D. A male cannot be a carrier because his genetic makeup is XY; thus, the presence of the mutation would result in the disease.