The diploid number of the hypothetical animal Geneticus introductus is 2n= 44. Each diploid nucleus contains 5 ng of DNA in G1. Part A : What amount of DNA is contained in each nucleus at the end of S phase? What amount of DNA is contained in each nucleus at the end of phase? a)There are 22 chromosomes containing 2.5 ng of DNA. b)There are 44 chromosomes containing 5 ng of DNA. c)There are 44 chromosomes containing 10 ng of DNA. d)None of the above. Part B: Write the number of chromosomes and amount of DNA (ng) present per cell at the end of Telophase I of meiosis (after cytokinesis). Express your answer as two numbers separated by a comma (example: 12, 4). Part C: Write the number of chromosomes and amount of DNA (ng) present per cell at the end of Anaphase of mitosis. Part D: Write the number of chromosomes and amount of DNA (ng) present per cell at the end of Telophase II of meiosis (after cytokinesis). Solution The cell cycle of actively dividing eukaryotic cell consists of gap phases (G 1 and G2), S phase and M phase. In G 1 phase the cell prepares for cell division .In S phase DNA replication occurs and the DNA content doubles. In G 2 phase, the cell gets ready for mitosis. In mitosis, two daughter cells with same genetic content as parent are produced. Mitosis occurs through five stages: prophase, prometaphase, metaphase, anaphase and telophase. Prophase: This stage extends over half of mitosis. The nuclear membrane disintegrates. The centrosome of chromosome duplicates to form two daughter centrosomes and migrates to opposite poles of the cell. The centrosomes organise the production of microtubules, from which the spindle fibres arise. The chromosomes condense and consist of two identical chromatids (or sister chromatids) held together at the centromere. Prometaphase: The chromosomes, move to the middle of the cell. The spindle fibres bind to centromere of each chromosome at kinetochore. Metaphase: The chromosomes align along the metaphase plate of the spindle apparatus. Anaphase: This is the shortest stage of mitosis. The centromeres divide, and the sister chromatids of each chromosome are separated and move to the opposite poles of the cell. The separated sister chromatids ordaughter chromosomesreceives a copy of each parental chromosome. Telophase: This is the final stage of mitosis. The nuclear membrane reforms, the chromosomes uncoil, and the spindle fibres disappear. Cytokinesis: the membrane appears to divide the two daughter cells with same chromosome number and the DNA content as the parent cell. The cell then enters interphase - the interval between mitotic divisions. Meiosis is the cell division occuring in sex cells or gametes (which contain a single copy of each chromosome). The process involves one DNA replication followed by two successive nuclear and cellular divisions (Meiosis I and Meiosis II). Similar to mitosis, meiosis is preceded by a process of DNA replication that converts each chromosome into two sister chrom.

1. The diploid number of the hypothetical animal Geneticus introductus is 2n= 44. Each diploid
nucleus contains 5 ng of DNA in G1.
Part A : What amount of DNA is contained in each nucleus at the end of S phase? What amount
of DNA is contained in each nucleus at the end of phase?
a)There are 22 chromosomes containing 2.5 ng of DNA.
b)There are 44 chromosomes containing 5 ng of DNA.
c)There are 44 chromosomes containing 10 ng of DNA.
d)None of the above.
Part B: Write the number of chromosomes and amount of DNA (ng) present per cell at the end of
Telophase I of meiosis (after cytokinesis). Express your answer as two numbers separated by a
comma (example: 12, 4).
Part C: Write the number of chromosomes and amount of DNA (ng) present per cell at the end of
Anaphase of mitosis.
Part D: Write the number of chromosomes and amount of DNA (ng) present per cell at the end of
Telophase II of meiosis (after cytokinesis).
Solution
The cell cycle of actively dividing eukaryotic cell consists of gap phases (G 1 and G2), S phase
and M phase. In G 1 phase the cell prepares for cell division .In S phase DNA replication occurs
and the DNA content doubles. In G 2 phase, the cell gets ready for mitosis.
In mitosis, two daughter cells with same genetic content as parent are produced. Mitosis occurs
through five stages: prophase, prometaphase, metaphase, anaphase and telophase.
Prophase: This stage extends over half of mitosis. The nuclear membrane disintegrates. The
centrosome of chromosome duplicates to form two daughter centrosomes and migrates to
opposite poles of the cell. The centrosomes organise the production of microtubules, from which
the spindle fibres arise. The chromosomes condense and consist of two identical chromatids (or
sister chromatids) held together at the centromere.
Prometaphase: The chromosomes, move to the middle of the cell. The spindle fibres bind to
centromere of each chromosome at kinetochore.
Metaphase: The chromosomes align along the metaphase plate of the spindle apparatus.
Anaphase: This is the shortest stage of mitosis. The centromeres divide, and the sister chromatids
of each chromosome are separated and move to the opposite poles of the cell. The separated
sister chromatids ordaughter chromosomesreceives a copy of each parental chromosome.
Telophase: This is the final stage of mitosis. The nuclear membrane reforms, the chromosomes

2. uncoil, and the spindle fibres disappear.
Cytokinesis: the membrane appears to divide the two daughter cells with same chromosome
number and the DNA content as the parent cell.
The cell then enters interphase - the interval between mitotic divisions.
Meiosis is the cell division occuring in sex cells or gametes (which contain a single copy of each
chromosome). The process involves one DNA replication followed by two successive nuclear
and cellular divisions (Meiosis I and Meiosis II). Similar to mitosis, meiosis is preceded by a
process of DNA replication that converts each chromosome into two sister chromatids.
Meiosis I reduces the cell from diploid to haploid. This stage separates the pairs of homologous
chromosomes. It consists of the following stages.
Prophase I: The homologous chromosomes pair and exchange DNA to form recombinant
chromosomes. It has five phases:
Leptotene (chromosomes condense),
Zygotene (homologous chromosomes undergo synapsis to form bivalents consisting of four
chromatids),
Pachytene (crossing over between homologous pairs of chromosomes to form chiasmata),
Diplotene (separation of homologous chromosomes except at chiasmata) and
Diakinesis (complete seperation of homologous chromosomes ).
Prometaphase I - Formation of spindle apparatus and attachment of chromosomes
Metaphase I - Bivalents (homologous pairs of chromosomes ) are arranged along the metaphase
plate as double row.
Anaphase I - Separation of the homologous chromosomes and migration to the opposite poles of
the cell.
Telophase I -The chromosomes uncoil and the nuclear membrane reforms.
Cytokinesis- The final cellular division to form two new cells, and is followed by Meiosis II.
Meiosis I is a reduction division. The original diploid cell with two copies of each chromosome
after division into the new haploid cells have one copy of each chromosome.
Meiosis II
Meiosis II separates each chromosome into two chromatids. The events of Meiosis II are similar
to those of mitosis, but the number of chromosomes has been halved.
Based on the above facts chromosome number and DNA content at various phases can be
deduced.
Phases of division
No: of chromosomes
DNA (ng)
G 1

3. 44
5
S
44
10
G 2
44
10
Mitosis-Anaphase, Telophase
88
10
After cytokinesis
44
5
Meiosis I
44
10
Meiosis II
22
5
After cytokinesis
22
2.5
Part A: c. There are 44 chromosomes containing 10 ng of DNA.
Part B: (44, 5)
Part C: (88,10)
Part D: (22, 2.5)
Phases of division
No: of chromosomes
DNA (ng)
G 1
44
5
S
44
10

4. G 2
44
10
Mitosis-Anaphase, Telophase
88
10
After cytokinesis
44
5
Meiosis I
44
10
Meiosis II
22
5
After cytokinesis
22
2.5