Question

if a fruit fly has 8 chromosomes, how many chromosomes would it have after synthesis takes place?
8 chromosomes
16 chromosomes
46 chromosomes
92 chromosomes

which of the following steps in the cell cycle belong to mitotic (m) phase?
g1 & s
g2 & mitosis
mitosis & cytokinesis
s phase & cytokinesis

which stage is this cell in?

Explanation:

First Question:

Step1: Recall DNA synthesis (S phase)

During the S phase (synthesis phase) of the cell cycle, DNA replication occurs. Each chromosome is duplicated, so the number of chromosomes (counted as the number of distinct structures, but after replication, each chromosome has two sister chromatids, but the chromosome number (count of centromeres) doubles? Wait, no—wait, the question is about a fruit fly, which has 8 chromosomes (diploid, 2n = 8). During S phase, DNA replicates, so each chromosome becomes two sister chromatids, but the number of chromosomes (as in the number of centromeres) would be... Wait, no, actually, the number of chromosomes (counted by centromeres) doubles? Wait, no, 2n = 8. After S phase, the cell is still 2n, but each chromosome has two chromatids. Wait, maybe the question is phrased as "how many chromosomes would it have after synthesis (S phase) before mitosis?" Wait, the options are 8, 16, 46, 92. Wait, fruit fly has 8 chromosomes (2n = 8). During S phase, DNA replicates, so the number of chromatids doubles, but the number of chromosomes (centromeres) is still 8? No, wait, no—wait, maybe the question is a typo, or maybe I misremember. Wait, no—wait, the options: 8, 16, 46, 92. 46 is human diploid, 92 after S. But fruit fly is 8. Wait, maybe the question is "how many chromatids?" but the options say chromosomes. Wait, maybe the question is wrong, but assuming it's a human cell? No, the first line says "a fruit fly has 8 chromosomes". Wait, maybe the question is "how many chromosomes would it have after synthesis (S phase) before mitosis?" Wait, during S phase, each chromosome is replicated, so the number of chromosomes (as in the number of DNA molecules) doubles? No, chromosomes are counted by centromeres. So 2n = 8. After S phase, the cell has 2n chromosomes, but each chromosome has two sister chromatids. So the number of chromosomes (centromeres) is still 8, but the number of chromatids is 16. But the options include 16. Wait, maybe the question is using "chromosomes" to mean chromatids? So if a fruit fly has 8 chromosomes (2n = 8), after S phase, each chromosome is duplicated, so the total number of chromatids (which some might incorrectly call chromosomes) would be 16. So the answer would be 16? Wait, but the options are 8, 16, 46, 92. So 16 is an option. Wait, maybe the question is "how many chromosomes (chromatids) would it have after synthesis?" So 8 chromosomes (original) each duplicate, so 16 chromatids, which might be called 16 chromosomes in some contexts. So the answer is 16? Wait, but the first option is 8, second 16. So maybe the answer is 16.

Step2: Check options

The options are 8, 16, 46, 92. Fruit fly 2n = 8. After S phase, DNA replicates, so each chromosome (2n = 8) becomes two sister chromatids, so the total number of chromatids is 16, which is sometimes referred to as 16 chromosomes (though technically, chromosomes are counted by centromeres, so 8 chromosomes with two chromatids each). But the options include 16, so the answer is 16.

The Mitotic (M) phase of the cell cycle includes Mitosis (the division of the nucleus) and Cytokinesis (the division of the cytoplasm). The other phases: G1, S, and G2 are part of Interphase. So the steps in M phase are Mitosis and Cytokinesis.

The cell in the image (with chromosomes aligned at the equator, spindle fibers attached, and the cell shape) looks like Metaphase of Mitosis. In Metaphase, chromosomes are lined up at the metaphase plate (equator) of the cell, attached to spindle fibers.

Answer:

16 chromosomes (the option with 16 chromosomes)

Second Question: