Somatic cells of chimpanzees contain 48 chromosomes. How many chromatids and chromosomes are present at (a) anaphase of mitosis, (b) anaphase I of meiosis, (c) anaphase Il of meiosis, (d) G1 prior to mitosis, (e) G2 prior to mitosis, (f) G1 prior to meiosis l, and (g) prophase of meiosis l? How many chromatids or chromosomes are present in (h) an oogonial cell prior to S phase, (i) a spermatid, (j) a primary oocyte arrested prior to ovulation, (k) a secondary oocyte arrested prior to fertilization, (l) a second polar body, and (m) a chim panzee sperm?

During both mitosis and meiosis, DNA replicates first during S phase of interphase. Each copy (DNA molecule) is called chromatid. Before anaphase they remain together, joined by the centromere in the chromosome.

Part 1: How many chromatids and chromosomes are present at:

(a) anaphase of mitosis: During this phase sister chromatids split. We would have 48 chromosomes in each pole and 48 chromatides.

(b) anaphase I of meiosis: During this phase homologous chromosomes split, being a reductional division. In each pole we will have half the chromosomes we had after DNA replication. This is 24 chromosomes but 48 chromatides (remember they will split during anaphase II).

(c) anaphase II of meiosis: This is an equational division, we will have 24 chromosomes in each pole and 24 chromatides. Each chromatid is considered a chromosome.

(d) G1 prior to mitosis: During this phase DNA has not replicated yet and it is not condensed either. This formed is called chromatin. We will assign one chromatid for each chromosome. This is a somatic cell, so: 48 chromosomes and 48 chromatids.

(e) G2 prior to mitosis: After S phase, we have duplicated all chromosomes. We will assign two chromatids per chromosome: this is 96 chromatides and 48 chromosomes.

(f) G1 prior to meiosis: Before DNA duplication, 48 chromosomes, 48 chromatids.

(g) Prophase of meiosis I: After DNA replication, condensation of the chromatin takes place: 48 chromosomes, 96 chromatids.

Part 2: How many chromatids or chromosomes are present in:

(h) An oogonial cell prior to S phase: This is G1 phase, 48 chromosomes.

(i) A spermatide: This is the male haploid gametid, after meiosis: 24 chromosomes and 24 chromatids.

(j) A primary oocyte arrested prior to ovulation: They are arrested at prophase I of meiosis. This means their DNA is still duplicated and chromatides have not divided yet. 48 chromosomes and 96 chromatids.

(k) A secondary oocyte arrested prior to fertilization: They are halted at metaphase II of meiosis, meaning they have half the chromosomes (24) but chromatids are still together (48).

(l) A second polar body: They suffered the same process as the mature ovum but remained with little cytoplasm. They have 24 chromosomes and 24 chromatids.

(m) A chimpanzee sperm: They have completed both meiosis as well, they have 24 chromosomes and 24 chromatids.