DNA is genetic material and is packaged in chromosomes

Transcription Translation
DNA---------------->RNA-------------->Protein

1 gene = 1 protein

Traits are referred to as if they are due to single genes but may be due to numerous genes.

Diploid (2n) organisms have chromosomes which occur in matched pairs, so each gene has at least one copy.

Forms of a gene are called alleles, diploid organisms can have two different forms but more than two forms can be present in a population.

Population = group of interbreeding individuals.

If two alleles for a gene are the same in an individual, that individual is homozygous for that gene. If different forms are present, then individual is heterozygous.

New alleles arise via DNA mutations (natural and artificially induced causes)

Meiosis - one partner of every pair of chromosomes goes to one of the nuclei.

Codominant and dominant alleles - handout.

Plants can be characterized as outcrossing (gametes come from different plants), inbreeding (gametes come from same plant) or apomictic (produces seeds without fertilization). In agriculture inbreeding refers to fusion of gametes from different but genetically similar plants.

Outcrossing can be obligatory if flowers are self-incompatible. Primulaceae is an example.

Hybrids are produced by a cross between two different species or between divergent members of the same species. Hybrids are favored because they often have hybrid vigor - produce more and larger seeds. Hybrids are often sterile due to chromosome incompatibilities. One way to break through the sterility barrier is via polyploidy. Polyploids contain more than the diploid # of chromosomes. Polyploids occur naturally and can also be induced artificially.

Breeding - takes advantage of inbreeding to produce homozygous individuals.

Inbred, homozygous lines can be produced by crosses between one of the parents with the offspring or crosses between offspring. Inbred lines can then be used to produce hybrids.

Example - take a wild plant with a desirable trait that is closely related to an agriculturally important crop. Cross wild with cultivar-----> F1 with desirable trait but not homozygous. Go through series of backcrosses and selection until you essentially have the cultivar + the desirable trait.

Often, improvements in cultivated plants have a deleterious effect on germ plasm base of those crops (germ plasm base = genetic variation present in wild progenitors, relatives and land races of a particular plant). Cultivation of hybrids in centers of origin of crop plants can greatly reduce germ plasm base.

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