Basics to Genetics

What is genetics?

Genetics are the characters that we poses and is the branch of biology which deals with study of genes, heredity and variations in genes. 

  • Inheritance and Genetics:

 So first of all we will learn some terms so that understanding the concepts related to genetics becomes very easy. Let's first know these two terms – Inheritance and Genetics. How the characters of parents are transmitted to their progeny, their children that process is called inheritance. And when we study the variations found in a population of a species that study, or that process is called genetics.

 There are various types of variations that are found in a species take an example of human species like 'height', there are so much variations seen in the height, skin complexion, eye colour. We also study occurrence of such variations in genetics.

  • Traits:

And next term is 'trait'. Trait means a particular feature of an organism. We find many external and internal features when we study an organism if we talk about external features then height is a trait of a species. If we again talk about human, then height, skin complexion and eye colour - all these are different traits.

  • Chromosomes and Factors:

Basics to Genetics

Next term is chromosome. It occurs in nucleus. Chromosome is Long thread like structure that consists of DNA and proteins. A chromosome is composed of a large number of linearly ordered genes these are called units of inheritance. Genes are present on chromosomes when we study Mendelism.

 Mendel used a term in his studies – “factor”. These factors are actually genes. Mendel discovered many principles of genetics but by that time neither chromosomes nor genes were discovered therefore he called those units 'factors' in his studies.

  • Alleles:

 Next term is alleles. When we talk about genes - they define a particular feature. Features of an organism are expressed due to genes. Alternative forms of a gene are called alleles. If we talk about pea plant we have learnt about a little genetics in our schools.
We used T and t for pea plant's height. These are two alternative forms of height of pea plant. Pea plant's height is a trait, a particular gene is responsible for this trait. Now the two alternative forms of this gene T and t, we call these two forms as the alternative alleles of the gene of height.

 Alleles contains slightly different genetic information. If they express height, both of these two different forms will express height differently T expresses tallness, t expresses shortness. Alternative forms of a gene are called alleles. 

  • Types of Alleles:

Now we will know these two terms - Homozygous Condition and Heterozygous Condition. First of all we must know that every individual has two alleles of a particular genes. Alleles occur in pairs every trait is expressed by one gene. And two alternative forms of a gene may occur in an organism. A person inherits one allele from his father and the other allele form his mother so, alleles occur in pair in an individual.

 If both the alleles are identical then that condition is called Homozygous Condition. For example if a pea plant has TT it means that this pea plant has inherited T from its father and mother then this condition is called Homozygous Condition.
 But if an individual inherits different alleles for a particular trait, from both parents then that condition is called heterozygous Condition. In pea plant contains Tt, it inherited T from one parent and t from the other then this condition is called heterozygous Condition.

 There’s one more term - Hemizygous condition. what is Hemizygous?  For example when we study 'sex chromosomes' then we find this XY condition in male if we talk about human these XY or XX are sex chromosomes. But these are two different sex chromosomes. These are not two different copies of a single gene. These are two different genes such a condition is called Hemizygous condition.

  •  Genotype and Phenotype:

The next two terms are - Genotype and phenotype. Presentation of alleles of a particular genes, when we study that particular trait then it is called Genotype. For example in a pea plant, TT  are present when we express in this way then we are writing its genotype. 
And Phenotype is the physical expression of a trait. For example as TT expresses tallness, in the same way tt expresses shortness but we cannot make out genotype from the phenotype.

 What does it mean is, if we know that the genotype is TT then we are sure that this pea plant must be tall. But if a pea plant is tall then we cannot make out its genotype whether it is TT or Tt because both the genotypes have only one phenotype that is tallness.

 If a pea plant has the genotype TT or Tt then expression of both the genotypes and phenotypic expression is the same and that pea plant is definitely a tall plant. 

  • Dominant and Recessive Traits:

Next comes - Dominant Trait and Recessive  Trait. In heterozygous genotype, it has two alternative forms of alleles. But the allele which expresses itself we call that allele a dominant allele. For example if a genotype of a pea plant is Tt then only T expresses itself. t will not express itself in presence of T then T is called dominant. t which is not able to express itself in heterozygous condition, is called Recessive allele. It will be able to express itself -  when it is present in homozygous condition. If an organism has tt then only t will be able to express itself then that organism will be short. 

  • Bonus knowledge!!!

 Wild and Mutant Alleles. Wild and Mutant Alleles are the original allele- when evolution was started the first evolved original allele, that genetic form is called wild allele. That allele is always dominant in a population.

If we talk of pea plant, then the first allele evolved for height was T when mutation occurred in T then it formed the second allelic form t so, the allelic forms which are evolved due to mutation in wild alleles are known as mutant alleles. The first evolved allelic form, it is dominant also, is called the wild allele.

 There can be more than one mutant alleles. Let us understand the point if we talk about pea plant then it has two allelic forms for height - T and t. It means that pea plant has only one mutant allele for height that is t.

 But when we talk about eye colour in humans, original allele must have been for the 'black eyes' now the mutant forms are evolved due to which many eye colours evolved like blue, green, grey. All those alleles are mutant alleles and are more than one.  

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