Dominant and Recessive Dominance

Table 3

Alleles• sequence of DNA• any of several forms of a gene• determine the genotype (genetic

constitution of an organism or a group of organisms) of their host organism

Dominant Alleles• expressed over the recessive allele• represented by capital letters• determines the phenotype (any observable

characteristic of an organism) of an organism

Recessive Alleles• hidden by it's dominant partner but still

present in heterozygous individuals (an organism that has two copies of the same allele)

• only expressed when there are two recessive alleles

• represented by lower case letters

Genes• a unit of heredity in a living organism• a region of DNA that controls a hereditary

characteristic• carries biological information in a form that

must be copied and transmitted from each cell to all its progeny

Dominant Genes• causes a person to have a particular physical

characteristic• when written in a genotype is always written

before the recessive gene in a heterozygous pair (two different forms of a particular gene)

• a person only needs to inherit one copy of the gene for the trait to be expressed

Recessive Genes• can only be expressed in homozygous (aa)

individuals (an organism that has two copies of the same allele)

• has its expression masked in the presence of a dominant gene

• a person needs to inherit two copies of the gene for the trait to be expressed

Traits • a distinguishing characteristic or quality• come from our genes, which are unique to

each person

Dominant Traits• will manifest when only one copy of the

gene is present• will be possessed as long as you inherit it

from either of your parents

Recessive Traits• can be carried in a person's genes without

appearing in that person• will be possessed only if you inherit it from

both parents