Science 1.9 Key Words

Words you must learn

Allele
Different forms of the same gene. They can be dominant or recessive.
Trait
A genetically determined characteristic.
Genotype
The particular alleles of an organism.
Phenotype
The observable characteristics of an individual resulting from its genotype.
Purebred
An organism that is homozygous for a particular trait.
Homozygous
An individual with two alleles that are the same for a particular trait.
Heterozygous
An individual with two alleles that are different for a particular trait.
Pedigree Chart
A diagram that shows the phenotypes of related individuals.
Test cross
A cross between an organism whose genotype for a certain trait is unknown and an organism that is homozygous recessive for that trait so the unknown genotype can be determined from the offspring.
Dominant
An allele which is always expressed, even if only one is present. Expressed with an upper-case letter (i.e. ‘A’).
Recessive
An allele which is only expressed when two of them are present. Expressed with a lower-case letter. (i.e. ‘b’).
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