HEREDITY AND GENETICS

How heredity is passed from

parent to offspring through genes

Key VocabularyTrait: a characteristic that is inherited from parents

DNA: the material that carries our traits

Gene: a part of the DNA that has our traits on it

HOW DID I GET MY BROWN EYES…… Traits are passed between generations by

genetic coding of chromosomes. One or more gene pairs may control a trait.

Each parent contributing one gene forms a pair of genes.

With a simple genetic characteristic, one gene pair controls the trait. If a gene’s trait is more prominent in the individual, that gene is said to code for the dominant trait. (ex. Brown eyes)

If the gene’s trait is less prominent in the individual, the gene is said to code for the recessive trait.

The ability to curl your tongue is a trait that is controlled by one gene pair. A dominant gene will allow you to curl your tongue. A recessive gene will not give you this ability.

If either or both of the genes in your pair is dominant you will be able to curl your tongue.

If both the genes in your pair are recessive, you will not be able to curl your tongue.

When both genes are the same, they are called

homogeneous. If both parents are homogeneous for

the recessive trait, all offspring will display the recessive trait because they have only recessive genes.

If both parents are homogeneous for the dominant trait, all the offspring will display the dominant trait because they have only the dominant genes.

When the gene pair is mixed with a dominant and recessive gene, it is called heterogeneous.

Individuals that have heterogeneous genes display only the dominant trait.

Many people who curl the their tongues (dominant trait) have heterogeneous genes (one dominant, one recessive).

The offspring of heterogeneous parents show either recessive or dominant traits depending on which gene was passed on to the child.

The mixture of traits in the offspring then is the result of the chance event of the recessive or dominant trait being passed on to the child.

This mixture can be predicted using probability.