Question

Determine the diploid numbers of the following organisms from the per cell observations given below:

a) 16 tetrads at metaphase I

b) 60 chromatids at metaphase I

c) 12 centromeres at anaphase I

d) 12 centromeres at anaphase II

e) 20 chromosomes at anaphase of mitosis

Answer 1

There are two types of cell division Meiosis and Mitosis.

Meiosis is the reductional division, occurs during gamete formation of sexually reproducing diploid organisms. Two rounds of division occurs and results in 4 daughter cells from one parental cell.

There are 9 stages of this cell division,

Prophase I

Metaphase I

Anaphase I

Telophase I

prophase II

Metaphase II

Anaphase II

Telophase II

Cytokinesis

In prophase I, chromosome condensed, crossing over occurs. At late prophase I microtubules attach to the kinetochore from the pole.

In metaphase I , pairs of homologous chromosomes arranged in metaphase plate.Both chromatids are attached to kinetochore microtubules from two poles.

During Anaphase I, Homologs moves toward opposite pole after the breakdown of sister chromatids cohesion.

In Telophase I, each half of the cell possess a haploid set of chromosomes. Cytokinesis simultaneously occurs and forms two haploid daughter cells.

Then in Prophase II, a spindle apparatus forms. Microtubules attach to the chromatids.

Metaphase II, metaphase plate forms as in mitosis.Microtubules attach to the kinetochore of sister chromatids, extend to opposite pole.

In Anaphase II, Chromatids moves toward opposite pole as individual chromosomes.

In Telophase II, haploid daughter cells forms. Chromosomes starts decondensing, cytokinesis occurs.

Total 4 daughter cells produced.

a) So, 16 tetrads at metaphase I , then the diploid number of the organism is 32.

b)60 chromatids at Anaphase I, the diploid number of the organism is 30.

c) 12 centromere at Anaphase I , Diploid number is 12.

d) 12 centromere at Anaphase II means the diploid number of the organism is 12.

e)20 chromosomes at Anaphase of Mitosis, the diploid number of the organism is 10.

Mitosis is equal division. Here 2 daughter cells produced with same chromosome number as parent cells. This type of cell division occurs in every cell.