Question

question 21 2 pts what proteins are crucial for creating and maintaining dna replication forks? choose the best explanation.
helicase creates the replication fork; single - strand binding proteins keep the single strands from reuniting.
helicase creates the replication fork; primase keeps the single strands from closing shut.
ligase creates the replication fork; dna polymerase ii keeps the single strands from reuniting.
question 22 2 pts in one statement, what is sexual reproduction?
the production of two haploid cells, one from each of two parents, and the subsequent fusion of two diploid cells to form a single, unique aneuploid cell.
the production of two haploid cells, one from each of two parents, and the subsequent fusion of two haploid cells to form a single, unique diploid cell.
the production of two diploid cells, one from each of two parents, and the subsequent fusion of two diploid cells to form a single, unique tetraploid cell.

Explanation:

Question 21

To determine the correct answer, we analyze the roles of proteins in DNA replication:

• Helicase unwinds the DNA double helix, creating the replication fork.
• Single - strand binding proteins (SSBs) bind to the single - stranded DNA regions and prevent them from re - annealing (reuniting).
• Primase is responsible for synthesizing RNA primers, not for keeping single strands from closing. Ligase is involved in joining Okazaki fragments, not creating the replication fork. DNA polymerase II is involved in DNA repair and not in keeping single strands from reuniting. So the first option is correct.

Sexual reproduction involves the production of haploid gametes (one from each parent) through processes like meiosis. Then, these two haploid gametes fuse (fertilization) to form a diploid zygote.

• In the first option, the fusion of two diploid cells to form an aneuploid cell is incorrect. Aneuploidy is an abnormal chromosome number, and sexual reproduction results in a diploid cell.
• In the third option, the production of diploid cells from parents and fusion of diploid cells to form a tetraploid cell is incorrect as parents produce haploid gametes. The second option correctly describes sexual reproduction: production of two haploid cells (gametes) from two parents and fusion of two haploid cells to form a unique diploid cell.

Answer:

A. Helicase creates the replication fork; single - strand binding proteins keep the single strands from reuniting.

Question 22