Pedigree Analysis

Which of the following is a characteristic of autosomal dominant inheritance?

• The trait skips generations.

• Both males and females are equally likely to be affected.

• Only males are affected.

• The trait is only passed from mother to child.

Answer explanation

In autosomal dominant inheritance, both males and females have an equal chance of being affected, as the trait is not linked to sex chromosomes. This rules out the options that suggest gender bias or skipping generations.

In a pedigree chart, what does a filled square represent?

• An affected female

• An unaffected male

• An affected male

• An unaffected female

Answer explanation

In a pedigree chart, a filled square indicates an affected male. This visual representation helps identify individuals with a specific trait or condition, distinguishing them from unaffected males, who are represented by unfilled squares.

Which genetic disorder is caused by an autosomal recessive mutation?

• Huntington's disease

• Cystic fibrosis

• Marfan syndrome

• Haemophilia

Answer explanation

Cystic fibrosis is caused by an autosomal recessive mutation in the CFTR gene. In contrast, Huntington's disease is autosomal dominant, Marfan syndrome is autosomal dominant, and Haemophilia is X-linked recessive.

In X-linked recessive inheritance, which of the following is true?

• Females are more frequently affected than males.

• Only females are affected.

• Both males and females are equally affected.

• Males are more frequently affected than females.

Answer explanation

In X-linked recessive inheritance, males are more frequently affected than females because they have only one X chromosome. If that X carries the recessive allele, they will express the trait, while females need two copies to be affected.

Which genetic disorder is caused by an autosomal dominant mutation?

• Huntington's disease

• Cystic fibrosis

• Haemophilia

• Sickle cell anaemia

Answer explanation

Huntington's disease is caused by an autosomal dominant mutation, meaning only one copy of the mutated gene is needed for the disorder to manifest. In contrast, cystic fibrosis, haemophilia, and sickle cell anaemia are caused by recessive mutations.

Which of the following is true about autosomal recessive inheritance?

• More common in males.

• Often only a single affected case.

• Each affected person normally has one affected parent

• Never transmitted from father to son.

Answer explanation

In autosomal recessive inheritance, a trait only appears if both copies of the gene are mutated. So both parents need to have the mutation. It won't be seen in them as they only have one copy of the mutation. So carriers are more common and people who have both mutations are more rarely seen in families.

In a family tree analysis, what does a horizontal line connecting a circle and a square represent?

• Siblings

• Divorce

• Parent-child relationship

• Marriage

Answer explanation

In a family tree, a horizontal line connecting a circle (female) and a square (male) represents marriage. This indicates a union between the two individuals, distinguishing it from other relationships like siblings or parent-child.

Which genetic disorder is caused by an X-linked recessive mutation?

• Cystic fibrosis

• Marfan syndrome

• Huntington's disease

• Duchenne muscular dystrophy

Answer explanation

Duchenne muscular dystrophy is caused by an X-linked recessive mutation, affecting primarily males. In contrast, cystic fibrosis, Huntington's disease, and Marfan syndrome are not X-linked recessive disorders.

Which of the following is a characteristic of autosomal recessive inheritance?

• The trait can skip generations.

• The trait is passed from mother to daughter.

• The trait is passed from father to son.

• The trait is only present in males.

Answer explanation

In autosomal recessive inheritance, traits can be carried by individuals without being expressed, allowing them to skip generations. This means that the trait may not appear in every generation, making 'the trait can skip generations' the correct choice.

In X-linked inheritance, which of the following is true?

• The trait is passed from mother to son.

• The trait is passed from father to son.

• The trait is passed from father to daughter.

• The trait is passed from mother to daughter.

Answer explanation

In X-linked inheritance, the trait is carried on the X chromosome. Males inherit their X chromosome from their mother, so the correct statement is that the trait is passed from mother to son.