Allele: The things that determine the trait. They are one of a group of genes that occur at a specific location (locus). It’s more precise to say “allele” rather than “gene” because there can be several alleles within one gene.

Dominant: A trait that masks the presence of the other allele. The dominant trait is the one that shows up.

Incomplete dominance: A phenotypic appearance that is a combination of both alleles. (red x white = pink)

Co- Dominance: A phenotypic appearance that is a segregated areas of each allele. (red x white = red and white spotted, Roan)

Recessive: A trait that doesn’t show unless the person carries two alleles for it. The recessive trait will hide if the person also carries the dominant trait.

  • Dominance and recessiveness are not actually allelic properties. Rather, they are effects that can only be measured in relation to the effects of other alleles at the same locus.

Genotype: What you look like in your genes. It may not be what actually shows.

Homozygous: The same, like when you have two of the same allele for some trait. For instance, if you have two alleles for blue eyes, you are homozygous for that trait.

Heterozygous: Mixed, like when you have two different alleles for some trait. For instance, if you have one blue-eyed allele and one brown-eyed, you are heterozygous for that trait.

Hybrid: This means heterozygous or mixed. In a Punnett Square, it’s written with one big letter and one small one, like this: Tt.

Mendelian Traits: These are traits governed by only one genetic locus (fancy word for “place”) and only two alleles. These are also called “simple traits.”

Phenotype: What you look like on the outside. You can be phenotypically (now there’s a long word!) brown-eyed even if you carry one allele for brown eyes and one for blue, because the brown eyes are what are showing in you.

Principle of Segregation: This says that for any trait, the pair of alleles from each parent separate and only one of them is passed on to their child. This means that, even though your mom and dad each have two alleles for each trait they have, they only pass on one to you you get one from each of them. That’s fair, right?

Punnett Square: The grid that is used to map out potential offspinrg genotypes using the parental genotypes


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