Diseases Associated with Sex Chromosomes Quiz

Answer: haemophilia

The recessive genes for haemophilia are carried on the X-chromosome. For a male to suffer from the disease, he need only inherit one affected X-chromosome (from his mother). For a female to suffer from haemophilia, she must inherit two affected X-chromosomes (that is, from both parents). If a female inherits only one affected X-chromosome, then she will be a carrier but not suffer from the disease.

Hence, it is mostly males who suffer from haemophilia.

Answer: red-green colour-blindness

Daltonism is named after John Dalton, an English physician and chemist. Dalton was the first person to identify and study colour-blindness. Dalton and his brother were both colour-blind so his interest in this subject was natural. Red-green colour-blindness is a X-linked recessive disorder.

Answer: muscular dystrophy

Muscular dystrophy is not a single disease; it is a group of diseases, all of which are inherited and characterised by progressive weakness and degeneration of muscle tissues. Duchenne's muscular dystrophy is the most common form. It is an X-linked recessive disorder.

It is almost always seen in boys, most of whom die before the age of 20. Not all forms of muscular dystrophy are sex-linked.

Answer: fragile X syndrome

Fragile X syndrome is associated with a fragile, constricted area near the end of the long arm of an X-chromosome. Unlike most sex-linked disorders, it affects both males and females because it is an X-linked dominant condition. However, the symptoms are variable and males tend to experience more severe symptoms than females.

Some affected individuals show mental retardation while others show no symptoms at all.

Answer: Ishihara colour test

The genes for colour-blindness are carried on the X-chromosome and are recessive. The Ishihara test consists of a series of pictures made up of multi-coloured dots. People with normal colour vision can see numbers amongst the dots whereas people with colour-blindness cannot distinguish anything at all. The test is named after Shinobu Ishihara, a Japanese ophthalmologist.

Answer: because the Y-chromosome carries very few genes

The Y-chromosome carries very few genes. It carries the genes that determine "maleness" and the gene for "hypertrichosis of the pinna". That's medical terminology for hairy ears. Maleness is determined by a single gene on the Y-chromosome called TDF (testis determining factor).

Answer: hairy ears

Since this gene is carried on the Y-chromosome, it cannot be passed down from father to daughter and women cannot be carriers. It is passed from father to son.

Answer: they are hermaphrodites (have both male and female reproductive organs)

Turner's syndrome is a genetic defect in women where there is only one X-chromosome instead of two. The designated abbreviation is XO (instead of XX which is the normal female). A Y-chromosome is not present so they never have male characteristics. The syndrome was named after Dr Henry Hubert Turner, an American endocrinologist.

Answer: XXY (patient appears to be male)

Klinefelter's syndrome is a genetic disorder in which there are three sex chromosomes, XXY. Affected patients appear to be male with small testes which fail to produce sperm. Other features include enlarged breasts, absence of facial and body hair and a tall, thin build. This disorder is named after Harry F. Klinefelter Jr, an American physician.

Answer: haemophilia

Many of the royal families of Europe are descended from Queen Victoria. She was a carrier of haemophilia and she passed the gene on to her son, Leopold, who had the disease, and her daughters Alice and Beatrice who were also carriers. There was no history of haemophilia in Queen Victoria's ancestors, so the popular theory is that a spontaneous mutation occurred on one of the X-chromosomes of her parents, or in her own embryonic cells (although some have questioned her alleged paternity). Through the marriages of her children, the gene affected many of the royal families of Europe, although the British royal family was one branch which escaped this inheritance.