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Patterns of Inheritance

Aunt Maggie says you have your father's eyes.
Grandma says you have your mother's smile.

Could you actually have the traits from these other people? If you are genetically related to them then yes, you could. Half of your genes are from your mother and half are from your father. But you might look more like one of them than the other. Why is that? Genes are shuffled during meiosis, bringing together different mixes of genes in each gamete. Thus, your brother might look more like one of your parents while you look more like the other.

Within each of the trillions of cells in your body are chromosomes. Chromosomes come in pairs. You got one chromosome of each pair from your mother and one from your father. Along each chromosome are genes, one for each trait. This means that you have two copies of each gene, one from your mother and one from your father. Both genes of a pair deal with the same trait, but they might differ in their information about it. For instance, one gene for eye color might say blue while the other one says brown.

  • If the two genes are actually the same, for instance, if both genes give instructions for blue eyes, then the genes are called homozygous.
  • If the two are different, for instance, if one is for blue eyes and the other is for brown eyes, then the genes are called heterozygous.

In a heterozygous situation, the two genes have different instructions. Often one of those genes wins out and its instructions are carried out (that's called the dominant gene). The other one is still present but its instructions are not carried out (that's called a recessive gene). As a custom, people designate dominant genes with uppercase letters and lowercase genes with lowercase letters. For example gene "A" is dominant and gene "a" is recessive.

The genes of an individual are called its geneotype. They determine what it will look like, which is called its phenotype!

Last modified February 29, 2008 by Lisa Gardiner.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA