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Biology Chapter 6

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Genetics
the scientific study of heredity
trait
a characteristic that can be passed from parent to offspring
purebred
a plant or organism that receives the same genetic traits from both of its parents.
hybrid
an organism that receives different forms of a genetic trait from each parent
Genes
sections of a chromosome that code for a trait
allele
a distinct form of a gene
dominant allele
a form of a gene that is fully expressed when two different alleles are present
recessive allele
a form of a gene that is not expressed when paired with a dominant allele
Chromosome theory of heredity
states that the material of inheritance is carried by the genes in chromosomes
genotype
the genetic make up of an organism
phenotype
The outward expression of the trait in an organism
homozygous
an organism in which the two alleles in a gene pair are identical
heterozygous
an organism in which the two alleles for a particular trait are different
Punnett square
a grid for organizing genetic information
test cross
when geneticists breed the organism whose genotype is unknown with a homozygous recessive organism
pedigree
a chart that shows how a trait and the genes that control it are inherited within a family
carrier
an individual who carries a recessive trait that is not expressed
incomplete dominance
When two different alleles for the same trait combine but neither allele "wins" expression over the other, the offspring have a form of intermediate inheritance
codominance
both alleles in the heterozygote express themselves fully
Polygenic trait
a trait controlled by two or more genes
multiple alleles
if three or more alleles are found in the population
Pleiotropy
When a single gene affects more than one trait