Q.7 What is Genotype? Explain its different types.
Answer:
Genotype
The specific combination of genes in an individual is known as the genotype of that individual. It is of two types:
(i) Homozygous . (ii) Heterozygous
(i) Homozygous Genotype
The genotype in which the gene pair contains two identical alleles (AA or aa) is called as homozygous genotype. ‘
(ii) Heterozygous genotype
The genotype in which the gene pair contains two different alleles (Aa) is called as heterozygous genotype.
Explanation with example Albinism
It is a condition in which normal body pigments are absent. Like other traits, it is also controlled by one pair of genes.
Recessive trait
Albinism is recessive trait i.e., it is produced when both recessive alleles are present in an organism
Alleles for a trait
Two alleles for a gene pair are represented’ as ‘A’ and ‘a’. Allele ‘A’ produces normal body pigments while allele ‘a’ does not produce pigments.
Three combinations
Three combinations i.e. genotypes are possible for these two alțeles.
(i) AA (ii) Aa (iii) aa
Dominant allele
In heterozygous condition one allele masks or prevents the expression of other. It is called as dominant allele and it is represented by capital letter.
Recessive allele
In heterozygous condition, one allele is not expressed, it is called as recessive allele. It is always represented by lower case letters.
Genotype AA or Aa
If genotype is ‘AA’ or ‘Aa’, the individual will produce pigments.
Genotype aa
If genotype is ‘aa’, no pigments will be produced and individual will be albino,
Conclusion
So it is concluded that allele ‘A’ dominates allele ‘a’ because in ‘Aa’ individual pigments are produced and the effect of a’ is suppressed by ‘A’.
Phenotype
The expression of genotype in the form of trait (in albinism, being albino or having normal pigmentation) is known as phenotype.
