How many centromeres are present in a bivalent and how many bivalents are present in a diploid cell of human females respectively?

Options

A. 2 and 46
B. 23 and 23
C. 2 and 23
D. 1 and 23

Answer

To solve the question regarding the number of centromeres in a bivalent and the number of bivalents in a diploid cell of human females, we can break it down into two parts.

### Step 1: Determine the number of centromeres in a bivalent.
- A bivalent is formed when homologous chromosomes pair up during the process of synapsis in meiosis.
- Each homologous chromosome consists of two sister chromatids, resulting in a structure that contains four chromatids in total.
- However, each homologous chromosome has one centromere. Since there are two homologous chromosomes in a bivalent, the total number of centromeres in a bivalent is:
\[ \text{Number of centromeres in a bivalent} = 2 \]

### Step 2: Determine the number of bivalents in a diploid cell of human females.
- A diploid cell contains two sets of chromosomes, denoted as \(2N\). In humans, \(N\) (the haploid number) is 23, which means a diploid cell has a total of:
\[ 2N = 2 \times 23 = 46 \text{ chromosomes} \]
- Each bivalent is formed by the pairing of two homologous chromosomes. Therefore, the number of bivalents formed in a diploid cell can be calculated as:
\[ \text{Number of bivalents} = \frac{\text{Total number of chromosomes}}{2} = \frac{46}{2} = 23 \]

### Conclusion:
- The number of centromeres in a bivalent is 2.
- The number of bivalents in a diploid cell of human females is 23.

Thus, the final answer is:
- **2 centromeres in a bivalent and 23 bivalents in a diploid cell of human females.**