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

Which of the following types of mutation would not be expected to detect in a molecular diagnostic test which is based on sequencing each exon of a gene in genomic DNA from a male suspected of having a X-linked disorder?

  1. Missense mutation

  2. Nonsense mutation

  3. Deletion of an exon

  4. Inversion of part of the gene
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

An inversion of part of the gene would not cause the exons to be absent or missing, and the sequencing reaction would not reveal that the exons are no longer arranged in the proper order on genomic DNA.

Multiple choice

A couple seek molecular testing for prenatal diagnosis of an autosomal recessive condition. The haplotype in coupling with the mutation is found in both parents by analysis of the parents and the affected offsprings. Analysis of chorionic villus tissue from the embryo reveals that the embryo inherited only the maternal haplotype in coupling with the mutation. What would you counsel them?

  1. The developing embryo is most likely a carrier.

  2. The developing embryo could be affected if recombination occurred in the father.

  3. The developing embryo could be homozygous unaffected if recombination occurred in the mother.

  4. All of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

According to the question, all of the above statements are possible.

Multiple choice

A sequence-based molecular diagnostic test reveals that an affected child has a missense mutation in a gene known to be associated with a dominantly-inherited disorder. The child is the first member of the family to be affected, and the disorder is associated with complete penetrance. The mutation has never been seen before, either in affected individuals or in controls. Which of the following would be the most powerful evidence that the mutation is pathogenic?

  1. Test both parents to see if the mutation is found only in the child.

  2. Determine whether the mutation affects an amino acid that is conserved in evolution.

  3. Examine the structure of the protein to see if the mutation has a major effect on protein function.

  4. Review the literature to see if the mutation has been reported to be pathogenic.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The child is expected to have a new mutation, given that the disorder displays complete penetrance and both parents are unaffected. One would therefore predict that the mutation would not be found in either parent (although germline mosaicism would be possible).

Multiple choice

The most significant limitation of molecular analysis of the HFE gene for screening for hemochromatosis in individuals of northern European descent is

  1. non-penetrance

  2. allelic heterogeneity

  3. locus heterogeneity

  4. variable expression
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A significant proportion of individuals who are homozygous for an HFE mutation will not develop signs or symptoms of iron overload. There are only two HFE mutations that account for most affected individuals, and HFE mutation accounts for the majority of cases of hemochromatosis in individuals of northern European descent.

Multiple choice

Which of the following is a major limitation of DNA-based carrier screening in cystic fibrosis?

  1. Laboratory errors in mutation analysis

  2. Nonpenetrance of many CFTR mutations

  3. Germline mosaicism

  4. Incomplete ascertainment of mutations
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The current approach to carrier detection involves testing of a limited panel of mutations, which results in failure to detect some of the rarer CFTR mutations. Negative carrier testing does not mean that an individual is not a carrier, though negative testing reduce an individual's risk of being a carrier.

Multiple choice

Brett's syndrome is a rare form of mental retardation that can be more or less severe depending on the gender of the parent from whom it is inherited. This unusual kind of inheritance pattern is known as

  1. modifying gene

  2. genome imprinting

  3. incomplete penetrance

  4. codominance
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When genes have different effects depending on the gender of the parent from whom they were inherited, it is referred to as genome imprinting. Diabetes, psoriasis, and Prader-Willi syndrome are other examples of this phenomenon.

Multiple choice

A 15 year old boy develops a disorder, which is present in his father and no one else in the family is known to be affected. Which of the following modes of inheritance is least likely?

  1. Autosomal recessive

  2. Autosomal dominant

  3. X-linked recessive

  4. Sex-linked dominant
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

An X-linked trait does not display male to male transmission. Any of the others are possible, including autosomal recessive, if the mother is also heterozygous (pseudo-dominant transmission).