Questions: Question 6 1 pt When homologous chromosomes cross over, what is the result? Two sister chromatids exchange identical pieces of DNA. Two sister chromatids get tangled, resulting in one altering the sequence of its DNA. Each of the four DNA strands of a homologous pair is broken, and the pieces are mixed. Specific proteins break the two strands of nonsister chromatids and re-join them. Question 7 1 pts

The answer is the fourth one: Specific proteins break the two strands of nonsister chromatids and re-join them.

Explanation for each option:

1. Two sister chromatids exchange identical pieces of DNA.

   • This is incorrect. Sister chromatids are identical copies of each other, so exchanging pieces would not result in genetic variation, which is the purpose of crossing over.

2. Two sister chromatids get tangled, resulting in one altering the sequence of its DNA.

   • This is incorrect. Tangling of sister chromatids does not typically result in sequence alteration. Crossing over involves nonsister chromatids of homologous chromosomes, not sister chromatids.

3. Each of the four DNA strands of a homologous pair is broken, and the pieces are mixed.

   • This is incorrect. While crossing over involves breaking and rejoining DNA strands, it specifically involves nonsister chromatids, not all four strands.

4. Specific proteins break the two strands of nonsister chromatids and re-join them.

   • This is correct. During crossing over, specific proteins facilitate the breaking and rejoining of DNA strands between nonsister chromatids of homologous chromosomes, leading to genetic recombination.

In summary, crossing over involves the exchange of genetic material between nonsister chromatids of homologous chromosomes, facilitated by specific proteins.