Traits and Inheritance

There are two sets of “instructions” for each characteristic. Scientists call these instructions for an inherited trait genes. Each parent gives one set of genes to the offspring. The offspring then has two forms of the same gene for every characteristic – one from each parent. The different forms (often dominant and recessive) of a gene are known as alleles. Dominant alleles are shown with a capital letter, Recessive alleles are shown with a lower case letter.

Phenotype Genes affect the traits of offspring. An organism’s appearance is known as its phenotype (FEE no type). This means what traits are showing or visible.

Genotype Both inherited alleles together for an organism’s genotype. For example someone with a “Bb” genotype for eyes would have brown eyes, but they carry genes for both brown eyes and blue eyes. Two of the same type of gene = homozygous Two different types of genes = heterozygous

Punnett Squares A punnett square is used to organize all the possible combinations of offspring from particular parents.

What are the chances? The mathematical chance that something will happen is known as probability. This is usually written as a fraction or a percent. Each parent has 2 alleles for each gene. A parent is equally likely to receive either allele.

More About Traits Genes are more complicated that Mendel knew when he was looking at peas. There can be irregularities. Incomplete dominance can happen when one trait is not completely dominant over another. They don’t blend together, but each allele has it’s own influence. Some traits can be changed by your environment. Sun can change skin color, your diet can influence if you reach your full height potential, etc.

One Gene, Many Traits – Sometimes one gene can influence more than one trait. For example, white tigers have blue eyes. The trait for white fur and blue eyes is carried in the same gene. Many Genes, One Trait – Some traits, like eye, hair, and skin color, are the results of several genes acting together. This is why the shade of your eyes might be different that your parents, even if the color is the same.