Genetics is the study of heredity or how characteristics of living organisms are transmitted from one generation to another.
This course cover the following:
- Understand genes and biological inheritance.
- Identify DNA and RNA.
- Explain DNA replication, transcription, and translation/protein synthesis.
- Identify various kinds of mutations.
- Understand genetic engineering, types, and its application.
- Explain Human molecular genetics.
Understanding this process of heredity or inheritance is important as this determines the uniqueness of every individual organism (Figure 1).
Genes are segments of DNA located in the chromosomes. They exist in more than one form. These alternative forms are called alleles, which typically appear in pairs.
Genes are transmitted from parents to an offspring. This transmission determines the genetic constitution of the offspring as well as the appearance of one or more attribute of the offspring.
Genotype and Phenotype
This is a result from the interaction of its genetic constituents and the environment.
Genotype is the genetic constituents of the individual as determined by genes. Phenotype is the physical characteristics expressed in an individual, i.e. the individual actually has the particular physical characteristic or trait present.
Both environment and genes affect phenotype of an individual. The genotype of identical twins are the same but their phenotypes (such as skin color) can be different due to environmental factors.
Genes are transmitted through both asexual and sexual reproduction. In asexual reproduction, such as budding or regeneration, offspring are genetically identical to a single parent.
However, offsprings formed by sexual reproduction can resemble either or both parents.
Categories of Biological Inheritance
Biological inheritance occurs in a variety of ways. Hence, inheritance can be categorized into types depending on criteria such as the chromosomes involved, loci involved, genotypic, or phenotypic expression of genes.
Based on presence of loci on the type of chromosome, biological inheritance is categorized into five types (Figure 2).
- Autosomal: Loci not present on a sex chromosome
- Gonosomal: Loci present on a sex chromosome
- X-chromosomal: Loci present on X chromosome
- Y-chromosomal: Loci present on Y chromosome
- Mitochondrial: Loci present on the mitochondrial DNA
Based on the number of loci involved biological inheritance are classified into three types (Figure 3).
- Monogenetic: one locus involved
- Oligogenetic: a few loci involved
- Polygenetic: many loci involved
A particular allele or trait is either dominant, recessive, or co-dominant, depending on how it interacts with other alleles.
Dominant and recessive inheritance are useful concepts to predict the probability of an individual inheriting certain characteristics from its parents.
Depending upon the expression of allele biological inheritance is classified into three types (Figure 7).
An allele is dominant if it masks the presence of other alleles. For example, dark eye color (Figure 4) is dominant over light eye color.
Heterozygotes show characteristics of two different alleles in co-dominant forms. For example, ABO blood types (Figure 5).
AB blood group has both A and B alleles present co-dominantly.
Recessive alleles are dominated by the dominant alleles. For example, attached earlobes (Figure 6) is a recessive trait over free forms.