Biology

Human Genetics and Disorders

882 Questions

Human Genetics and Disorders covers the inheritance patterns, genetic mutations, and molecular basis of hereditary diseases. Topics include sex-linked traits, cancer genetics, and metabolic disorders. This section tests knowledge critical for biology exams and general science papers.

Genetic mutationsInherited disordersCancer geneticsGenetic testingMendelian inheritance

Human Genetics and Disorders Questions

Multiple choice

Acute intermittent porphyria is due to defect in

  1. uroporphyrinogen III cosynthase

  2. porphobilinogen deaminase

  3. protoporphyrinogen oxidase

  4. coproporphyrinogen oxidase

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Acute intermittent porphyria (AIP) is caused by a deficiency of porphobilinogen deaminase (also known as hydroxymethylbilane synthase), which is the third enzyme in the heme biosynthesis pathway. This deficiency causes accumulation of porphobilinogen and ALA, leading to acute neurovisceral attacks. The other enzymes listed are deficient in different types of porphyria: uroporphyrinogen III cosynthase in congenital erythropoietic porphyria, protoporphyrinogen oxidase in variegate porphyria, and coproporphyrinogen oxidase in hereditary coproporphyria.

Multiple choice

Hydrops foetalis is due to the defect in the synthesis of

  1. Alfa-globin chain

  2. Beta-globin chain

  3. Delta-globin chain

  4. Gamma-globin chain
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Hydrops fetalis, specifically Hb Barts hydrops fetalis, results from homozygous alpha-globin gene deletion (--/--). Without alpha chains, gamma chains form Hb Barts (gamma4) which has extremely high oxygen affinity, causing severe tissue hypoxia and fetal death. Beta-globin defects cause other thalassemias but not hydrops fetalis.

Multiple choice

 Which tumour suppressor gene is mutated in families with familial adenomatous polyposis?

  1. APC

  2. p53

  3. BRCA1

  4. BRCA2

  5. VHL
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Mutations in the APC (adenomatous polyposis coli) gene cause both classic and attenuated familial adenomatous polyposis. These mutations affect the ability of the cell to maintain normal growth and function. Cell overgrowth resulting from mutations in the APC gene leads to the development of multiple colonic polyps. These polyps are not themselves malignant but are prone to develop frank carcinoma through the accumulation of further genetic mutations.

Multiple choice

Which of the following statements is INCORRECT regarding cancer in humans?

  1. Cancer is regarded a disease of old age.

  2. Skin cancers may bleed and look like sores.

  3. A cancer is a genetic disease, frequently being inherited.

  4. A cancer is caused by agglomeration of a small number of mutations, each of which boosts the cell with a growth advantage.

  5. A tumour in a cell is not considered malignant until it spreads to other parts of the body forming secondary tumours.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Cancer is regarded as a genetic disease because it is caused by mutations in the genome. However, these mutations are normally in somatic cells, not the germ cells and mutations contributing to cancer are rarely inherited. To form a malignant cancer, a cell must acquire a small number of mutations (probably about six) each of which gives the cell a growth or survival advantage.

Multiple choice

Which of the following is an autoimmune condition with the single most profound genetic association?

  1. Graves' disease

  2. Type1 diabetes

  3. Ankylosing spondylitis

  4. Rheumatoid arthritis

  5. IPEX (Immune dysregulation, polyendocrinopathy, enteropathy and X-linked syndrome)
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

By far, the vast majority of autoimmune diseases involve multiple genes together with environmental factors. IPEX is an example of an extremely small number of autoimmune diseases that are caused by a single gene defect. In this case, mutation of the Foxp3 gene results in a profound defect in regulatory T-cell activity.

Multiple choice

Mutations in the gene encoding which of the following, most commonly results in severe combined immunodeficiency (SCID)?

  1. Adenosine deaminase (ADA)

  2. Interleukin 7 receptor alpha chain

  3. Gamma C interleukin receptor component of the interleukin 15 receptor

  4. RAG 2 (recombination activating gene 2)

  5. Artemis
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Gamma C deficiency is responsible for about 40% of cases of SCID, and together with JAK 3 deficiency, results in a T-B+NK- phenotype. It is also utilized by the receptors for IL-2, -4, -7, -9 and -21.

Multiple choice

Anuj is suffering from pancreatic carcinoma. In pancreatic carcinoma the ras gene

  1. is absent

  2. contains a single point mutation, but not always at the same position

  3. is normal but is over expressed

  4. has a large deletion

  5. has large insertions
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A point mutation leads to a single amino acid substitution at either position 12, 13 or 61. These mutations are found in over 90% of patients with pancreatic carcinomas, in 40% of patients with colorectal cancers and their preneoplastic lesions, in acute myeloid leukemia (AML) and in preleukemic syndromes.