In these chromosomes at fixed positions called loci the genes are linearly distributed. Genes have different forms referred to as alleles. If the character represented by an allele is exhibited, it is considered as dominant allele. The character of that allele which is masked by the presence of dominant allele is referred to as recessive allele. If both the alleles represent a same character then the individual is said to be homozygous and if they are different then the individual is said to be heterozygous.
- The pattern of inheritance of mono genic traits may be anyone of the below three types. Autosomal dominant.
- Autosomal recessive.
- Sex linked.
Autosomal dominant inheritance of diseases.
In this case the dominant allele exhibits the disease condition. The male with Aa geno type is the diseased one and female with aa geno type is normal one. When these people mate, their gametes fuse in different combinations and half of the children will be heterozygous Aa and will be affected by the disease. Examples for autosomal dominant inheritance diseases are familial hypercholesterolemia, beta thalassemia, and breast cancer genes.
Autosomal recessive inheritance diseases.
In this case the recessive allele causes the disease .when a carrier male Aa and carrier female Aa mates the one fourth of the off springs will be affected by the disease. Examples for autosomal recessive inheritance diseases are sickle cell anemia, cystic fibrosis and phenylketonuria.
Sex linked inheritance diseases.
A when a normal male and carrier female mates half of the male child will be affected and no females will be affected. But half of the females will be carriers. Color blindness and hemophilia are good examples for sex linked inheritance.