Question

The scientific name for the common rat is Rattus norvegicus. This animal species is often used for genetic tests and serves as a model for many human diseases including arthritis, hypertension, diabetes, and cardiovascular diseases. It has a diploid chromosome number in its somatic cells of 2n=42, and its genome, which was sequenced in 2004, is estimated to have a 1C mass of 3.27 picograms (i.e., for the haploid, n=21, genome), which corresponds to about 3.34 million DNA base pairs (mbp).

Determine the following for the rat nuclear genome based on the information above.

a. How many homologous chromosome pairs would be present in a somatic cell?_______

b. What would the mass of the DNA be for a somatic cell (G1)?__________

c. What is the haploid (gametic) number for the Rat?_______

d. How many base pairs of DNA would you observe in cell that has completed G2? _______

e. Following fusion of egg and sperm to form a zygote, how many chromosomes would you observe in the nucleus?_______

f. How many tetrads would you observe in Rat in Metaphase I?________

Answer 1

Ans- Given : 2n = 42

n = 21 = 3.27 picograms = 3.34 mbp

a.) 20 pairs of autosomes and 1 pair of sex chromosome. Autosomal pairs of chromosomes are homologous chromosomes because they have same set of genes in the same order , while in sex chromosome one is X and the other is Y.

b.) Somatic cell in G1 have 2C . Mass of 1C = 3.27 pg. Therefore mass of 2C = 2 * 3.27 = 6.54 pg

c.) Haploid (gametic )number of the Rat is n=21 with 1C .I.e 3.34 mbp.

d.) Cells which have completed G2 phase have undergone through S phase, during which 2C content doubles up to 4C (DNA) content. Now 1C has = 3.34 million DNA bps. Therefore 4C will have = 4 * 3.34 = 13.36 million DNA bps.

e.) Each gamete be it egg or sperm, both will contain 21 chromosome each. So zygote formed after fusion will have 42 chromosomes in nucleus.

f.) 21 tetrads will be observed in Metaphase I .