Chromosome: Chromosomes are thread the structure made up of DNA molecules and histone protein which are found inside nucleus of cells.
Genes: Genes are tiny structures found In chromosomes. A Gene carry unit character. A chromosome consists of many genes.
Functions of chromosomes:
Chromosomes are responsible for transmission of heredity characters from parents to their offsprings.
Centromere: A constriction present in the chromosome is called centromere. On the basis of position of centromere
There are 4 types of chromosomes.
- Metacentric chromosome: When centromere lies at the middle of chromosomes, it is called metacentric chromosome.
- Sub-metacentric chromosome: When centromere lies near the middle of chromosome it is called sub-metacentric chromosome.
- Acro centric chromosome: When centromere lies near the end of chromosomal arms, it is called acro centric chromosome.
- Telo centric chromosome: When centromere lies at the end of the chromosomal arms it is called telo centric chromosome.
- Acentric chromosome: When centromere ie absent, it is called acentric chromosome
| Organism | Number (chromosomes) |
| Human | 46 (23 pairs) |
| House fly | 12 (6 pairs) |
| Frog | 26 (13 pairs) |
| Gorilla | 48 (24 pairs) |
| Onion | 16 (8 pairs) |
| Pine | 24 (12 pairs) |
| Horse | 64 (32 pairs) |
| Rice | 24 (12 pairs) |
| Sugar cane | 80 (40 pairs) |
| Patata | 48 (24 pairs) |
| Dog | 78 (39 pairs) |
| Solanum | 16 (8 pairs) |
Autosomes and sex chromosome:
Autosomes: Chromosomes which are responsible for baby characters are called autosomes. In human body, there are 22 pairs of autosomes.
Sex chromosome: Chromosomes which are responsible for the determination of sex of an individual are called sex chromosomes. In human being, thee are one pair sex chromosome.
On the basis of structure, there are two types of sex chromosome which are represented by X and Y.
Total chromosomes in male: 44 + XY
Total chromosomes in female: 44 + XX
Process of sex determination in Human:
Male consists of two different sex chromosomes i.e. X and Y so they produce two types of male gamete having sex chromosomes X or Y. In females chromosomes are similar i.e. XX so they produce only 1 type of female gamete having sex chromosome X. When male gamete with sex chromosome Y fertilizes female gamete, it forms male child (44 + XY). When male gamete carrying sex chromosome X fertilizes female gamete, it produces female child (44 + XX).
Chromosomal disorder: The disorder in the body caused due to change in the number of chromosomes is called chromosomal disorder. It is also called aneoploidy.
Some examples:
a. Down’s syndrome: First time it was explained by Langdon. The main cause of this disorder is addiction of extra copy of chromosome in chromosome number 21, it is called Trisomy of 21 of a gamete. Total number of chromosomes in this disorder is (45 + XX) or (45 + XX).
Symptoms:
- Short body with round head.
- Half opened mouth.
- Furrowed tongue.
- Palms are thick and creased.
- Person is physically and mentally retarded.
b. Klinefelter’s Syndrome: This problem is caused due to additional X chromosome (44 + XXY)
Symptoms:
- Person looks like male but infertile.
- Growth of breast, wider hips, abnormally tall.
- Poor muscle tone, low IQ.
c. Turner’s Syndrome: This problem is caused due to reduction in X chromosome (44+X0).
Symptoms:
- Person is infertile female.
- Short body structure.
- Less developed ovaries, short neck.
- Undeveloped sex organs.
Sex linked diseases: Those diseases which are seen only in particular gender are called sex-linked diseases. For eg, baldness is seen only in male and breast cancer is seen in female.
