To determine which genetic diseases exhibit a criss-cross pattern of inheritance, we need to understand what this term means. A criss-cross inheritance pattern typically refers to traits that are passed from father to daughter and then from daughter to son, often associated with genes located on the X chromosome. This is particularly relevant for X-linked recessive disorders.
Identifying the Correct Answer
Among the options provided, the correct answer is (a) Haemophilia and colour blindness. Both of these conditions are X-linked recessive disorders, which means they are carried on the X chromosome and predominantly affect males. However, females can be carriers and pass the trait to their sons, leading to the criss-cross inheritance pattern.
Understanding the Conditions
- Haemophilia: This is a bleeding disorder caused by a deficiency in clotting factors, primarily factor VIII or IX. Males who inherit the affected X chromosome will express the disease, while females need two copies of the mutated gene to show symptoms.
- Colour Blindness: This condition affects the ability to perceive colors correctly and is also linked to the X chromosome. Similar to haemophilia, males are more frequently affected, while females can be carriers.
Why Other Options Are Incorrect
Let’s briefly analyze the other options to clarify why they do not fit the criss-cross inheritance pattern:
- (b) Haemophilia, colour blindness, and hypertrichosis of the ear: While haemophilia and colour blindness are X-linked, hypertrichosis of the ear is a condition that can be inherited in an autosomal dominant manner, thus not fitting the criss-cross pattern.
- (c) Albinism and sickle cell anaemia: Both of these conditions are autosomal recessive disorders, meaning they do not follow the X-linked inheritance pattern and therefore do not exhibit criss-cross inheritance.
- (d) Klinefelter’s syndrome and Turner’s syndrome: These are chromosomal disorders rather than single-gene disorders. Klinefelter’s syndrome (47,XXY) affects males, while Turner’s syndrome (45,X) affects females, but they do not demonstrate criss-cross inheritance.
Conclusion
In summary, haemophilia and colour blindness are the only conditions listed that demonstrate a criss-cross pattern of inheritance due to their X-linked nature. Understanding these patterns is crucial for genetic counseling and predicting inheritance in families.
