Question

How are genes organized on a chromosome?

Answer 1

Hint: DNA is a genetic material that encodes all the necessary information about an individual. Two polynucleotide chains intertwined in a helical fashion makes up the DNA molecule. A set of nucleotides in the DNA that will code for a particular protein is called a gene. Genes are basically subunits of DNA molecules.

Complete answer:
- A DNA molecule in itself is really long, if stretched out it will not fit inside the nucleus. To combat this problem, the DNA molecule coils around proteins called histone. The DNA molecule now becomes a really dense version of itself. This is called the chromosome. This DNA can now easily fit inside the nucleus.
- The DNA has a definite nucleotide sequence. The genes express traits or characteristics of the organism. These traits are expressed because of a specific protein. Different genes expressing different traits are present in a chromosome. All genes have a definite position in the chromosome. The locus of a gene is the exact position where the gene of interest is found in the chromosome. On the chromosome there are many different loci, these loci give the exact position of the genes.
- Diploid organisms receive a pair of homologous chromosomes, one from the male parent and the other from the female parent. These homologous chromosomes have genes that code for the same characteristic. These genes are called alleles. Alleles code for the same trait but not identical trait i.e. one allele may code for blue eye colour and the other for brown eye colour.

Note: To find out the locus of the gene a genetic map or a physical map can be used. Physical maps represent the actual distance between genes.
The genetic map, however, only gives the location of the genes relative to one another. Some genes are linked i.e. they are physically so close to each other they are inherited together in a cell. Genetic maps use this particular information to find out gene loci.