A karyotype can only detect the chromosome number and any abnormalities when it comes to the chromosome count and structure. Trisomy 21 and Turner’s syndrome can be detected using a karyotype. However, since colorblindness occurs when there is a mutation in the gene located in the X-chromosome, it will not show in the karyotype.

D. II and III only

Among the choices, Duchenne muscular dystrophy, which results in the weakening of skeletal muscles, is the only condition caused by a sex-linked gene. Klinefelter’s syndrome and down syndrome are conditions caused by abnormalities in the sex chromosomes.

B. III only

Color blindness is considered an X-linked recessive disorder. In this case, X-linked alleles are always expressed in males. Male offspring who receives the defective X allele will be color blind, whereas female offspring will only have colorblindness if they receive two defective X alleles. If the female offspring receives only one defective X allele, she will only be a carrier of colorblindness. Considering these conditions, it is not possible that a male who carries a defective X allele will not have colorblindness. Therefore, C is the correct answer.

C. The father carries one allele but does not have colorblindness.

If one homozygous A-negative blood parent crosses with AB-negative blood type, the possible blood types of their offspring are 50% AB-negative and 50% A-negative. Therefore, there is zero possibility that their offspring will have a B-negative blood type.

A. 0%

According to the pedigree chart, the widow’s peak hairline is a dominant trait. Since both males and females have the trait, it is not linked to the sex. The trait is not also present because of two dominant alleles. Therefore, the pattern of inheritance is complete dominance. The principle of complete dominance indicates that the dominant alleles exhibit their effect in the form of a trait in an individual. On the other hand, recessive allele is masked by the dominant allele.

B. II only

Since the student do not have the dominant allele and her sister does, the possible genotypes of the parents of the student is Ww. The results of the cross, which is shown below, include WW, Ww, and ww. These combinations best fit the data in the pedigree chart.

E. Mother–Ww; Father–Ww

The widow’s peak hairline is a dominant trait which is represented by a capital letter W. Since the student do not have the dominant allele and her sister does, their genotypes would be ww (student), and Ww (sister).

C. Student–ww; Sister–Ww