Question

Normally, certain kinds of reiterated scquences occur in a chromosome as an interspersion pattern that is A. highly repetitive DNA sequences. B. the portion of DNA composed of single-copy DNA. C. Alu sequences. D. alternating blocks of single-copy DNA and moderately repetitive DNA. E. alternating blocks of short interspersed repeats and long interspersed repeats.

Short answer

Answer: Alternating blocks of single-copy DNA and moderately repetitive DNA.

Step-by-step solution

1. Introduction to highly repetitive DNA sequences

(A) Highly repetitive DNA sequences are short sequences that are repeated thousands of times in tandem arrangement (side by side) in the genome. These sequences are found mainly in centromeres and telomeres of chromosomes. Although these sequences are a part of interspersion patterns, they are not the interspersion pattern being referred to in the exercise.

2. Introduction to single-copy DNA

(B) Single-copy DNA refers to the unique sequences in the genome that are not repeated. These sequences often contain functional genes. This option is not correct as it refers only to unique sequences, not reiterated sequences.

3. Introduction to Alu sequences

(C) Alu sequences are short interspersed nuclear elements (SINEs) found in the human genome. They are about 300 base pairs long and are repeated over a million times in the human genome. While Alu sequences are a type of reiterated sequence, they are not the specific pattern mentioned in the exercise.

4. Alternating blocks of single-copy and moderately repetitive DNA

(D) Alternating blocks of single-copy DNA and moderately repetitive DNA is a more accurate description of the interspersion pattern that we are looking for in this exercise. Moderately repetitive DNA sequences are repeated a few times to several hundred times in the genome, and they include genes, pseudogenes, and some transposable elements. This type of organization allows for gene regulation and chromosomal stability.

5. Alternating blocks of short interspersed repeats and long interspersed repeats

(E) This option describes different types of interspersed repeats but is not the particular interspersion pattern being referred to. Short interspersed repeats (SINEs) and long interspersed repeats (LINEs) are both examples of moderately repetitive DNA sequences and are not organized in the alternating pattern described in this option. The correct answer is:

Answer:

D. Alternating blocks of single-copy DNA and moderately repetitive DNA.