Cell Division
Mitosis Cell Division
Significance of Mitosis Cell Division
Meiotic Cell Division
Significance of Meiotic Cell Division
Deoxyribonucleic acid (DNA)
Ribonucleic acid (RNA)
Chromosomes
Chromosomes are the microscopic substances that are contained in the nucleus of a cell and act as a vehicle of heredity. They are made up of DNA and proteins.
Genes
A gene is a tiny unit of heredity that transmits the parental characteristics to their offspring. It is made up of histone protein and DNA.
Types of Chromosomes
Somatic Chromosomes
Somatic chromosomes are the chromosomes that determine the physical characteristics of an individual.
They are also known as autosomes.
Sex Chromosomes
Sex chromosomes are the chromosomes that determine the sex of an individual.
They are also known as heterosomes.
Number of Chromosomes
In a specific organism, the number of chromosomes is generally constant. However, it may vary in different organisms. For example, the number of chromosomes in a normal human being is 46 whereas that in a normal gorilla is 48.
The following table represents the total number of chromosomes, in pairs, autosomes, and sex chromosomes in a few organisms.
| Organism | Number of Chromosomes | Number of Autosomes | Number of Sex Chromosomes |
| Human Beings | 23 | 22 | 1 |
| Frog | 13 | ||
| Rat | 20 | ||
| Tiger, Lion, Cat | 19 | ||
| Garden Pea | 7 | ||
| Chimpanzee, Gorilla | 24 | ||
| Yeast | 1 | ||
| Dog | 39 | ||
| Horse | 32 | ||
| Rice | 12 | ||
| Sugarcane | 40 | ||
| Onion | 8 | ||
| Housefly | 6 | ||
| Solanum | 8 | ||
| Pine | 12 |
Sex Determination in Humans
Sex determination is the process of determining the sex of a human being as boy or girl by the composition of chromosomes in their cells.
During copulation, a female ovule always contains two X chromosomes. In contrast, a male sperm may contain an X or a Y chromosome.
Combining an X chromosome from a female and another X chromosome from a male results in a girl.
Combining an X chromosome from a female and another Y chromosome from a male results in a boy.