Basic genetics：練習問題

In the ABO blood group system, a person with blood type B has a child with a person who has blood type O. If the person with blood type B is heterozygous, what are the possible blood types of their offspring?

A woman with normal vision, whose mother was colour-blind, marries a man with normal vision. What is the probability that their sons will be colour-blind?

Which of the following scenarios describes a true mutation event rather than a general chromosomal error or change in gene expression?

A pedigree chart of a family shows that a specific trait appears only in males, and every affected male has an affected father. Which of the following modes of inheritance is most likely for this trait?

Red-green colour blindness is an X-linked recessive trait. A woman with normal vision, whose father was colour-blind, marries a man with normal vision. What percentage of their total offspring are expected to be colour-blind?

In humans, what specific pair of chromosomes is responsible for sex determination?

In humans, haemophilia is a sex-linked recessive trait. Explain why a male is more likely to express this phenotype than a female.

In a species of flower, the allele for red petals (R) shows incomplete dominance with the allele for white petals (W), resulting in pink petals for heterozygous individuals. If two pink-flowered plants are crossed, what proportion of their offspring will display the pink phenotype? Explain your answer.

In a certain species of flowering plant, the allele for red flowers (R) is dominant over the allele for white flowers (r).

(a) A pure-breeding red-flowered plant is crossed with a pure-breeding white-flowered plant. State the genotypes of the parent plants and the $$F_1$$ generation. (2 marks)

(b) If two $$F_1$$ plants are crossed, what is the expected phenotypic ratio of the $$F_2$$ generation? (1 mark)

(c) Describe how you would determine the genotype of a red-flowered plant whose ancestry is unknown. (1 mark)

Cystic fibrosis is an autosomal recessive genetic disorder that affects various organs, primarily the lungs and digestive system. An individual must inherit two copies of the recessive allele to develop the disorder. Assume 'C' represents the dominant normal allele and 'c' represents the recessive allele for cystic fibrosis.

(a) A couple, both of whom are unaffected, have a child diagnosed with cystic fibrosis. What are the genotypes of the parents and the affected child? Explain how you arrived at these genotypes. (3 marks)
(b) If this couple has a second child, what is the probability that this child will be an unaffected carrier for cystic fibrosis? Show your working using a Punnett square. (2 marks)
(c) Briefly explain what a gene mutation is and how it leads to the production of the faulty protein associated with cystic fibrosis. (2 marks)