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6th Grade Science / Lesson 11 - Common Inherited Traits

Common Inherited Traits
What will we be learning today?


  • In this lesson, we are going to learn all about what are some of the common inherited traits.


What Are Some Common Inherited Traits?


  • Do you have any dominant traits? Freckles, long eyelashes, and free earlobes are dominant traits. Their opposite forms-no freckles, short eyelashes, and attached earlobes-are recessive.


Sickle-Shaped Cells


  • Some inherited traits in people are not as simple as dominant or recessive. One example is the shape of red blood cells. Red blood cells carry oxygen and nutrients to all parts of the body. Normal red blood cells have a round shape. Sometimes red blood cells are curved like the blade of a sickle. Sickle-shaped cells cannot carry as much oxygen as round cells.

    Sickle-shaped cells get their name because they are shaped like sickles. Sickles are curved cutting tools used in farming.


  • Let R stand for the gene for round red blood cells. R' stands for the gene for sickle-shaped cells.

  • Most people have the gene pair RR. That is, they have only round red blood cells.

  • People with R'R' genes have only sickle-shaped cells.

  • However, people may also inherit one R gene and one R' gene. They have both round and sickle-shaped cells. The genes for round cells do not hide the appearance of the genes for sickle-shaped cells.


Sickle Cell Anemia


  • Sickle-shaped cells cannot carry as much oxygen as normal cells. People who have two R' genes have the disease known as sickle cell anemia. Their body tissues and organs become damaged because the sickle-shaped cells cannot supply enough oxygen to keep them healthy. People with this disease can be treated with drugs to increase the amount of oxygen carried by their red blood cells. They may also be given transfusions of blood with normal red cells.

  • People who have inherited one R' gene and one R gene have the sickle cell trait. They have both normal and sickle-shaped blood cells. They are carriers of the disease but do not have the disease itself.


Blood Type


  • Blood type is another human trait that is not simply dominant or recessive. Three different genes control blood type. They are labeled Ia, Ib, and i. Ia and Ib are both dominant, masking i. Blood type genes A and B are not dominant for each other. The table shows how different combinations of these genes result in four blood types in humans.


Blood Types and Blood Donors


  • Each person has only one of the four types of blood-A, B, AB, or O. Your blood type is based on a kind of protein found on the surface of red blood cells. There are two such proteins, A and B. Type A blood has only the A protein. Type B has only the B protein. Type AB has both proteins. Type O does not have either of the two proteins.


  • If unmatching blood types are mixed, the blood can clump. In some cases clumping can be fatal. A person may receive blood from another person with the same protein or with no protein.

  • Type O blood can be donated to anyone. A person with type O blood is called a "universal donor

  • Type AB blood can only be given to a person with type AB blood. However, a person with type AB blood can receive all of the four types. That person is a "universal recipient."


Let's Review What We Learned Today!


  • Now complete your worksheet!