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Principle of Segregation

In the formation of gametes, the genes separate in such a way that each gamete is equally likely to contain either member of the pair.

Dominant trait

Expressed in the phenotype when the genotype is either heterozygous or homozygous

Recessive trait

Expressed in the phenotype when a genotype is homozygous for the alternative allele.

Principle of Independent Assortment

Segregation of the members of any pair of alleles is independent of the segregation of other pairs in the formation of reproductive cells.

Addition rule

The probability of the realization of one or the other of two mutually exclusive possibilities, A or B, is the sum of their separate probabilities

Multiplication rule

The probability of two independent possibilities, A and B, being realized simultaneously is given by the product of their separate probabilities

Variable expressivity

Genes that are expressed to different degrees in different organisms


Proportion of organisms whose phenotype matches their genotype for a given trait.


When one gene masks the expression of another

Key ingredients for PCR

Template DNA
DNA polymerase

Key steps for PCR


Fundamental limitation for PCR

Primer sequences MUST be known


Plasmids used for in vitro cloning of foreign DNA fragments

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