Question

Define Mendel’s two laws of inheritance

Define replication, transcription and translation and provide a general statement about the role each plays in gene expression.

Answer 1

1. The Law of Dominance: Mendel proposed the law of dominance to explain the results of the monohybrid cross. This law states that “when dissimilar (non-identical)pair of factor (Tt) come in a hybrid, one member of the pair dominate the expression of the other member of the pair”. This phenpmenon is called Law of Dominance. Eg In the heterozygote Tt; T dominates

2. Law of segregation/law of purity of gametes/universal law of Mendel

          Based on monohybrid phenotypic ratio [3:1]

· Applicable at the time of gametogenesis; therefore law of purity of gametes

· Time of segregation is anaphase I of meiosis, when homologous chromosomes and therefore the alleles separate.

The law states that “when dissimilar pair of factor (Tt) come in a hybrid, they do not mix or blend or contaminate each other. They separate or segregate when the hybrids form the gametes. Therefore one gamete contains 1 allele (1 factor) for each character. Therefore gamete is pure for an allele”

DNA is the genetic material of all organisms except some RNA viruses. Being the genetic material DNA is capable of making its own copies by a process called replication or duplication. DNA replication occurs immediately before cell division so that a copy of the genome can be transmitted from the parent cell to the daughter cell.

The process of synthesis of RNA from DNA is called transcription. The genetic information is stored in DNA in the form of a sequence of four types of nucleotides (adenine, Guanine, Cytosine and Thymine). During transcription the information present in DNA is copied down into an RNA.

Translation is the process by which proteins are synthesized according to the sequence information provided by the mRNA.

Gene expression means production of the product specified by the gene (i.e. RNA or protein). The product of a protein coding gene is protein, tRNA gene is tRNA and rRNA gene is rRNA. In the expression of a protein coding gene, the gene is first transcribed into an mRNA which is then translated into the corresponding protein. Transfer RNAs and rRNAs are never translated into proteins.