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Modern Genetics

Modern Genetics
Organismal Level

The production of gametes. Number of chromosomes is halved.  See Meiosis.

Genetic information is halved in specialized cells.

Occurs in sex tissues/organs of variable complexity from plants, roundworms, flies, etc.

Fertilization and Development

The reformation of complete set of chromosomes.  Differential gene expression (see Cellular Level) builds organism.

Complete set of genetic information is reconstituted. Information is selectively activated depending on developmental stage of organism  and cell type.

Single cell -> adult organism

Cellular Level

Only one copy of each duplicated chromosomes/DNA double helix distributed to daughter cells.  See Replication.

Genotype is faithfully duplicated and transmitted to daughter cells.

In the nucleus of eukaryotes; in the cytoplasm of prokaryotes.


Each chromosome pair* is halved independently of the others; following replication and pairing of homologous chromosomes. 

*In the case of higher ploidy, there will be more than two.

Genetic information is halved.  The alleles for each trait are separated, assuring one member of each pair in daughter cells.

In the nucleus of eukaryotes

Differential Gene Expression

The set of proteins polypeptides/proteins translated in a cell.

ssDNA templates for transcription are controlled by promotors, gene products, DNA modification, etc.

In the nucleus of eukaryotes, in the cytoplasm in prokaryotes.  Cytoplasmic interaction of gene products determines cell biochemistry.

Sub-cellular Level

Production of a polypeptide chain - the gene product/a series of amino acids. Requires an mRNA template, ribosomes and tRNA primed with amino acids.

Sets of three ribosomal nucleotides (triplets) determine the amino acid sequence making up polypeptide chain.

Occurs in the cytoplasm.


Information in the form of the nucleotide sequence of the coding strand of a gene (DNA) is transcribed into information in the nucleotide sequence of mRNA. Mutations (changes in the DNA template) result in changes in the information in the mRNA.


Synthesis of mRNA from nucleotide subunits (A,U,C,G).


Occurs in the nucleus of eukaryotes, in the cytoplasm in prokaryotes.


Faithful doubling of DNA (or RNA) from pool of nucleotides (A,T,C,G). Occasional changes in nucleotides = mutations.

Information in the form of the sequence of nucleotides in each strand of DNA is copied, resulting in two duplicate double strands. Each ssDNA is template for formation of new double helix.  Change in template = mutation.

Occurs in the nucleus of eukaryotes, in the cytoplasm in prokaryotes.