Lesson Plan - Get It!
What physical traits are common throughout your family? Are there any disorders or diseases that more than one person in your family has?
There are many genetic disorders, so we are going to focus on the most common.
They follow the same inheritance trend as other traits, including dominant, recessive, and sex-linked patterns. As you learned in the previous Related Lesson, these disorders can be visualized through family pedigrees. You will look at the pattern, symptoms, and treatment more in depth during this lesson.
Before continuing, if you missed or need to review the previous Related Lessons in our Human Inheritance series, find them in the right-hand sidebar.
Start by looking at some recessive genetic disorders. These disorders are only passed along when the child inherits two recessive alleles, which means that the parents must both be carriers of the disorder. Examples of recessive genetic disorders include Tay Sachs, Phenylketonuria, Cystic Fibrosis, and Sickle Cell Anemia.
Image by Kashmiri based on earlier work by Domaina, via Wikimedia Commons, is licensed under the Creative Commons Attribution-Share ALike 3.0 Unported license.
Notice how both parents have to be carriers in order for a child to inherit the disorder in the above image. If the trait is not carried on a sex chromosome, we call it an "autosomal trait." Individuals with most of these disorders can live with the symptoms, but death at a young age can occur for others.
Autosomal dominant disorders can be inherited with only one dominant allele. This means that if a parent is a carrier, he or she should consider the risks before having children. Carriers can pass the disorder on to male children more often; we will learn why that happens during this lesson. These disorders follow the inheritance pattern shown in this image:
Image by Domaina, via Wikimedia Commons, is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.
Dominant disorders, like Huntington's disease, can be devastating for patients. Some of these disorders start later in life, and that can make them harder to diagnose or treat. Dominant disorders include Huntington's disease and achondroplasia. Huntington's disease is a disorder where individuals lose control over their body functions as they age. Achondroplasia is dwarfism, where people are born with a gene that prevents bone growth.
Finally, sex-linked disorders are carried by the sex chromosomes, most often the X chromosome. These disorders often affect males, because they only inherit one X chromosome.
Image by the National Institues of Health, via Wikimedia Commons, is in the public domain.
In the sex-linked inheritance image, we can see that males are more likely to inherit the disorder. Daughters are more likely to become carriers, because they have a second X chromosome that can dominate the affected allele. Sex-linked disorders include hemophilia, muscular dystrophy, and red-blue colorblindness. Hemophilia is a blood disorder where a patient doesn’t stop bleeding easily. Muscular dystrophy causes a loss of muscle mass, which makes it hard for an individual to function easily. Red-blue colorblindness prevents people from seeing different colors!
Genetic disorders are passed through families the same way other physical traits are, through a blending of alleles and genes. Genetic disorders can lead to significant challenges in the life of a child or other patient.
Before moving on, discuss the three types of genetic disorders with a parent or teacher.
In the Got It? section, you will learn more about specific genetic disorders.