- Gene: It is the basic unit of inheritance. It consists of a sequence of DNA which is the genetic material. The genes
can mutate and can take two or more alternative forms.
- Chromosomes: These are thread-like structures of
nucleic acids and proteins that are found in the nucleus
of most living cells. They carry the heredity or genetic
information in the form of genes. These are made up of
nucleoproteins. German anatomist Waldeyer is known for
naming the chromosome. The number of chromosomes
varies from species to species but it remains constant for a
particular species. In most animals, however, any change
from the typical chromosome number for a species may
be due to genetic disorders.
- Genotype: It is the complete heritable genetic identity
of an organism. It is the actual setup of alleles that are
carried by the organisms.
- Phenotype: It is the description of the actual physical
characteristics of an organism, the way the genotype is
- Alleles: The alternative forms of the genes which arise
as a result of mutation. They are found in the same place
on the chromosome and af ect some characteristics or
traits but in alternative forms.
- Dominant alleles: When an allele affects the phenotype
of an organism, then it is a dominant allele. It is denoted
by a capital letter. For example- ‘T’ to express tallness.
- Recessive alleles: An allele that affects the genotype in
the absence of the dominant allele is called a recessive allele. It is denoted by a small letter. For example – ‘t’ for dwarfness.
- Homozygous: Each organism has two alleles for every
gene (each chromosome has one each). If both the alleles
are the same it is called homozygous. If tallness is the trait,
it is expressed as ‘TT’.
- Heterozygous: If the two alleles are different from each
other, then they are heterozygous in nature. If tallness is
the trait, then it is expressed as ‘Tt’.