The following are correct statements
(A) Nonallelic homologous recombination is due to the exchange of repetitive DNA located at different chromosomal locations.
(B) Chromosome duplication can change gene balance
(C) Chromosome inversion can change geme balance
(D)Williams syndrome is caused by chromosome duplication
(E) Paracentric inversion means that the centromere is in the inversion. Two correct answers for each question.
The correct answer and explanation is:
The correct answers are:
- (A) Nonallelic homologous recombination is due to the exchange of repetitive DNA located at different chromosomal locations.
- (B) Chromosome duplication can change gene balance.
Explanation:
- (A) Nonallelic homologous recombination: This type of recombination involves the exchange of DNA sequences between repetitive regions that are found at different locations on chromosomes. These repetitive sequences, often called “low-copy repeats,” can cause misalignment during meiosis. The result is the recombination of nonallelic chromosomes, which can lead to structural variations such as deletions, duplications, or inversions. Nonallelic homologous recombination is a key mechanism in generating genetic diversity and is also associated with certain genetic disorders due to the misalignment of chromosomal sequences.
- (B) Chromosome duplication can change gene balance: Chromosome duplication involves the replication of a portion of a chromosome, leading to multiple copies of certain genes. This extra genetic material can disrupt the normal balance of gene expression. When genes are duplicated, the gene dosage is altered, which can lead to developmental abnormalities or diseases, as the cellular machinery might be overwhelmed by excess protein production or improper regulation. For example, in certain forms of Down syndrome, there is a duplication of the 21st chromosome, leading to altered gene expression and developmental changes.
The other options are incorrect for the following reasons:
- (C) Chromosome inversion: While inversions can affect gene function by disrupting gene structure or regulatory regions, they do not necessarily change the overall gene balance. Inversions can lead to problems with chromosome pairing during meiosis, which may cause reduced fertility or result in nonviable offspring.
- (D) Williams syndrome: This disorder is actually caused by a deletion of genetic material on chromosome 7, not a duplication. It leads to intellectual disability and specific physical characteristics, such as a “elfin” appearance.
- (E) Paracentric inversion: This term refers to a type of inversion where the centromere is not included in the inverted region. If the centromere were part of the inversion, it would be classified as a pericentric inversion, which affects the structure and segregation of chromosomes more significantly.