Mention the total number of chromosomes along with the sex chromosomes that are present in a human female and a human male. Explain how in sexually producing organisms the number of chromosomes in the progeny remains the same as that of the parents.

In humans, the total number of chromosomes and the sex number of chromosomes differ between males and females. Let’s break down the details:

1. Total Number of Chromosomes in Humans

Humans have a total of 46 chromosomes in each somatic (body) cell, which includes both autosomes and sex chromosomes. This chromosome count is identical for both males and females.

2. Sex Chromosomes and the Sex Number

The sex number refers to the sex chromosomes, which determine the biological sex of an individual:

• Human Male: In a human male, the sex chromosomes are XY. This means the male has one X chromosome and one Y chromosome.
• Human Female: In a human female, the sex chromosomes are XX. This means the female has two X chromosomes.

3. Autosomes

Out of the total 46 chromosomes, 44 are autosomes (non-sex chromosomes), which are identical in both males and females, while the remaining 2 chromosomes are sex chromosomes (XX in females, XY in males). The sex number is the key difference between male and female chromosomes.

4. Chromosome Pairs

The 46 chromosomes in humans can be organized into 23 pairs. Each pair consists of one chromosome inherited from the mother and one from the father. The sex number influences how these chromosomes are inherited, with one of the pairs being the sex chromosomes that determine sex.

5. Ploidy Level in Humans

Human cells are diploid (2n), meaning that they contain two sets of chromosomes, one set inherited from each parent. This ploidy level is important for understanding how the sex number and other chromosomes are passed on to offspring.

6. Gametes and Fertilization

In sexually reproducing organisms, gametes (sperm and ovum) are produced through meiosis, a type of cell division that results in haploid cells (n). Each gamete carries half the chromosome number of a somatic cell, which is 23 chromosomes in humans, including a single sex chromosome.

When fertilization occurs, a male gamete (sperm) fuses with a female gamete (ovum) to form a zygote. This process restores the diploid (2n) chromosome number, with 46 chromosomes (23 pairs), including the sex number of chromosomes. The combination of these chromosomes determines the sex of the offspring.

7. Restoration of Chromosome Number

Through fertilization, the zygote receives half of its chromosomes from the mother (through the ovum) and half from the father (through the sperm). The sex number of the chromosomes is restored during fertilization, ensuring that the chromosome number in the progeny is the same as that of the parents.

Summary:

• Human Male: 46 total chromosomes (XY sex chromosomes)
• Human Female: 46 total chromosomes (XX sex chromosomes)
• The sex number of chromosomes determines the biological sex of the individual (XY for male, XX for female).
• The number of chromosomes in the progeny is maintained through the fusion of haploid gametes to form a diploid zygote, restoring the chromosome number, including the sex number of chromosomes, to that of the parents.