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Punnett Square:
Key Terms
Allele:One member of a pair of
genes occupying a specific spot on a chromosome that
controls the same trait.
Chromosome:A structure within the cell that bears
the genetic material of an organism.
Codominance:
A condition in which the alleles of a gene pair in a heterozygote
are fully expressed thereby resulting in offspring with a phenotype that is neither dominant nor recessive.
Example: AB Blood Type
Dominant Allele:
The allele that determines the phenotype of an
organism, masking the effect of the recessive allele when present.
Gamete:A reproductive
cell that contains the haploid set of chromosomes.
Gene:A segment of DNA that is responsible
for the phenotype of an organism.
Genotype:The entire set of genes
in an organism that determines the expression of a
particular phenotype.
Heredity:The passing of
genetic factors from parent to offspring.
Heterozygous:An organism containing two different alleles (a dominant
and a recessive) for a particular trait.
Homozygous:An organism containing two copies of the same
allele (two dominant or two recessive) for a particular
trait.
Homozygous Dominant:An organism that
has two dominant alleles (RR).
Homozygous Recessive:
An organism that has two recessive
genes (rr).
Incomplete Dominance:A kind of dominance occurring in
heterozygotes in which the dominant allele is only partially expressed. This usually results in offspring with an intermediate
phenotype because the organism has one dominant allele and one
recessive allele.
Genetic Locus: The location of a
gene on a chromosome.
Monohybrid Cross:
A crossbreeding experiment that follows the inheritance of a single characteristic across one or more generations. In other words this is a cross of one trait from two parents.
Multiple alleles: The existence of
several known alleles of a gene.
Phenotype:The physical
appearance of an organism as a result of the interaction of its genotype and the
environment.
Polygenic Trait: A trait that is controlled by two
or more genes at different loci on different chromosomes.
Examples: height, skin color, weight.
Recessive:An allele whose phenotypic expression is masked by a
dominant allele. The recessive trait may be expressed when the
recessive genes are in a homozygous condition.
Trait:A qualitative
characteristic. An attribute of
phenotype, not of genotype.
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