Basic terminology to start learning Genetics:

To learn genetics conceptually one needs to start from the very basic level. For that, we are going to start with the basic terminology. This will help you to learn Mendelian as well as post-Mendelian genetics with ease. We will also cover some previously asked conceptual questions as we proceed in this chapter.

Genetics: 

Genetics is that branch of biology in which we study inheritance and variation. Inheritance is the transfer of genetic materials from parents to offspring whereas variation is the changes that occur during inheritance of these genetic materials. Firstly we will try to learn inheritance by starting with the very basics.
Basic terminology to learn genetics: One must have knowledge about the basic terminology of genetics in order to master genetics so here we are starting from this very important terminology.
Character vs trait: Character is any phenotypic feature of an organism whereas trait is a state of a character.
For example Height of a plant is its character whereas the various states
of the character height such as tallness or dwarfness are the traits.
Eye color in humans is a character. The various forms in which eye color exists such as black or blue are the traits of this particular character.
 
Gene vs alleles:
 A  gene is any segment of DNA that encodes for a particular character whereas alleles are the alternate versions of that gene. Diploid organisms have two copies of each gene which may exist in alternate forms called alleles.
For example: In plants, there is a gene that controls the plant height. This gene may exist in two forms one form of that gene may encode for tallness whereas the other form of that gene may encode for dwarfness. Such alternate forms of
the genes are called alleles.

Locus: The specific position of a gene on a chromosome is called its locus. For example, the locus of gene A is shown in fig
Homologous chromosomes: Those chromosomes which have the same size, shape, same number, and position of genes are called homologous chromosomes. The homologous chromosomes form pairs. As we know that we inherit half of our chromosomes from our father and a half from our mother therefore, we end up with 23 pairs of homologous chromosomes. This can be simply understood with the fact that maternal chromosome no 1 is homologous and form pair with paternal chromosome no1. In the same way, all the 23 chromosomes in humans occur
in homologous pairs.
Phenotype: Any physical feature of an organism is called the phenotype. 
Example: Eye color, hair color, height, etc are phenotypes.
Genotype: The genetic makeup of an organism is called genotype. The genotype is responsible for the phenotype.
Example: If a plant's height is controlled by gene T. TT is responsible for the
tallness of the plant and is the genotype whereas tallness is the phenotype.


A diploid organism has two copies of each gene in its genome. so the genotype may exist as:
1. Homozygous: When there are the same copies of a particular gene at a particular locus of homologous pair of chromosomes then this condition of the genotype is called homozygosity and for that particular gene the individual is homozygous.
Example: If the genotype for the plant height is TT then it means both of the alleles are responsible for tallness and the plant is homozygous for that particular gene.
Similarly, if the genotype is tt, it means that both the alleles are for dwarfness and the plant is considered homozygous for that gene.
2. Heterozygous: An individual is heterozygous for a particular character if it carries different forms of the gene at the particular locus of the homologous pair of chromosomes.
Example: If a plant has genotype Tt for height then it means that the plant is heterozygous for the height character because it carries two different allelic forms of the gene T.
Genome: The complete set of chromosomes in an individual is referred to as its genome.
Example: In humans, there are two sets of chromosomes one from the maternal side and the other from the paternal side. If we consider any one of that set having 23 chromosomes it is termed as genome.
The sequence of genetic material from largest to smallest: This sequence will help you out in learning genetics conceptually.
Genome👉chromosomes👉genes👉DNA👉codons👉nucleotides