Question

Genetics

n is the basic number of chromosomes In humans 2n- 46 n-23 X is the number of chromosomes in a gamete or half the number of chromosomes of a diploid organism In humans 2x = 46 x 23

Answer 1

The number of chromosomes in a single set is called the haploid number, given the symbol n. Gametes (sperm and ova) are haploid cells. The haploid gametes produced by most organisms combine to form a zygote with n pairs of chromosomes, i.e. 2n chromosomes in total. The chromosomes in each pair, one of which comes from the sperm and one from the egg, are said to be homologous, i.e., having the same structural features and pattern of genes. Cells and organisms with pairs of homologous chromosomes are called diploid. Humans and most animals are diploid, but male bees, wasps, and ants are haploid organisms because they develop from unfertilized, haploid eggs.

In some cases, the n chromosomes in a haploid set have resulted from duplications of an originally smaller set of chromosomes. This "base" number - the number of apparently originally unique chromosomes in a haploid set - is called the monoploid number. For example, the chromosomes of common wheat are believed to be derived from three different ancestral species, each of which had 7 chromosomes in its haploid gametes. The monoploid number is thus 7 and the haploid number is 3 × 7 = 21. In general n is a multiple of x. The somatic cells in a wheat plant have six sets of 7 chromosomes: three sets from the egg and three sets from the sperm which fused to form the plant, giving a total of 42 chromosomes. As a formula, for wheat, 2n = 6x = 42, so that the haploid number n is 21 and the monoploid number x is 7. The gametes of common wheat are considered to be haploid, since they contain half the genetic information of somatic cells, but they are not monoploid, as they still contain three complete sets of chromosomes (n = 3x).

In the case of wheat, the origin of its haploid number of 21 chromosomes from three sets of 7 chromosomes can be demonstrated. In many other organisms, although the number of chromosomes may have originated in this way, this is no longer clear, and the monoploid number is regarded as the same as the haploid number. Thus in humans, x = n = 23.

Since, n is the multiple of x. so in the above slide, n will be the monoploid number which is 14 and x will be the total number of chromosomes of the progeny which is 28 and since it is the double of that of the progenitor species, it is denoted as 2x.

Therefore, n denotes the basic number of chromosomes, which is, monoploid and x denotes the total number of chromosomes of the progeny.