Autosomal Inheritance: Study with Video Lessons, Practice Problems & Examples

Autosomal inheritance involves tracking traits or disorders through generations, categorized as autosomal dominant or autosomal recessive. Autosomal dominant disorders require only one dominant allele for expression, appearing in every generation, while autosomal recessive disorders necessitate two recessive alleles, often skipping generations. For example, polydactyly is an autosomal dominant disorder, whereas cystic fibrosis is autosomal recessive. Understanding these patterns is crucial for predicting inheritance and assessing genetic risks in families.

Autosomal Inheritance

In this video, we're going to begin our lesson on autosomal inheritance. And so what's important to know is that a specific family trait or disorder can be tracked over multiple generations to identify the inheritance pattern. Now moving forward in our course, we're going to talk about two main types of inheritance patterns. And so the inheritance patterns can either be autosomal, or the inheritance pattern can be sex-linked. Now moving forward, we're first going to talk about autosomal inheritance and autosomal disorders, but then later in our course, in different videos, we'll talk more about the sex-linked disorders and sex-linked inheritance. But in our next video, we'll talk more about these autosomal disorders and inheritance. So I'll see you all there.

Autosomal Disorders

In this video, we're going to focus on autosomal disorders. And so traits or disorders that are associated with autosomes, which recall from our previous lesson videos are non-sex chromosomes, can be inherited in 2 ways that we have numbered down below, number 1 and number 2. And so the first way that these autosomal traits or disorders can be inherited is as autosomal dominant disorders. Now autosomal dominant disorders, as their name implies, are going to be disorders associated with autosomes in which individuals with at least one dominant allele will have the disorder. And so for example, the individual could either be homozygous dominant or heterozygous and still have the disorder because they have at least one dominant allele. Now dominant disorders tend to appear in every generation without skipping a generation. Now, the second way that autosomal disorders can be inherited is as autosomal recessive disorders. Of course, as their name implies, autosomal recessive disorders are disorders associated with autosomes in which the individuals that are homozygous recessive are going to be the ones that display the disorder. And so only individuals that have 2 lowercase letters for their genotype, or 2 alleles, will actually have the autosomal recessive disorder, which is different than having at least one capital, or one dominant allele, to have the disorder. Now autosomal recessive disorders, they tend to skip a generation. And so, if we take a look at our image down below, we can further distinguish between autosomal dominant disorders and autosomal recessive disorders pedigrees.

Over here on the left what we have is an autosomal dominant disorder. A disorder that's known as polydactyly which results in having extra digits, either extra fingers or extra toes. And so, because it is an autosomal dominant disorder that means that it's associated with the dominant allele. And so what you can see here is that having a capital F would result in having extra fingers or toes, or about polydactyly, whereas having the lowercase f would be having the normal number of fingers and toes. And so individuals that have at least one capital F are going to have polydactyly since it is an autosomal dominant disorder. And so notice that all of the ones that are shaded with the blue background are ones that are affected or that actually have polydactyly. And notice that all of them have at least one capital F, which is going to give them polydactyly. And all of the individuals that are not affected are going to be homozygous recessive and have 2 lowercase f's, and so the ones that are not affected are again not shaded.

Now over here on the right-hand side, what we're showing you is an autosomal recessive disorder, which is specifically cystic fibrosis. And so because cystic fibrosis is an autosomal recessive disorder, it's actually associated with the lowercase allele, the recessive allele, instead of being associated with the dominant allele. And so, individuals that have a dominant allele are going to be saved from having the disorder. They're gonna be healthy individuals. Whereas individuals that have 2 lowercase a's, individuals that are homozygous recessive, are going to actually have cystic fibrosis. And so that's exactly what we see over here in this pedigree. All of the shaded individuals are individuals that have the disorder, cystic fibrosis, and notice that all of them are homozygous recessive. And so, all of the ones that are not affected have at least one dominant allele to save them from having the disorder. Now one thing to note is that autosomal recessive disorders tend to skip an entire generation. And so notice that this generation here in the middle is not being affected, and the disorder seems to skip an entire generation. Whereas with autosomal dominant disorders, it tends to be present in every generation. And so this here concludes our introduction to autosomal disorders and distinguishing between autosomal dominant disorders and autosomal recessive disorders. And we'll be able to get some practice applying these concepts as we move forward in our course, so I'll see you all in our next video.

If a genetic counselor was examining a pedigree chart and noticed an occurrence of a disease in every generation, the counselor would most likely assume that the disease was caused by:

• A. A new reoccurring mutation.
• B. An autosomal recessive disorder.
• C. A chromosomal abnormality.
• D. An autosomal dominant disorder.
• E. Having an extra set of chromosomes.

The pedigree chart shown depicts the inheritance pattern of __________.

• A. An autosomal recessive characteristic with both parents being heterozygous.
• B. An autosomal dominant characteristic with both parents being homozygous dominant.
• C. An autosomal recessive characteristic with both parents being homozygous recessive.
• D. None.

Determine the likely pattern of inheritance in the following pedigree. List the genotypes of the numbered individuals in this order: #1, #2, and #3.

• A. aa, aa, aa.
• B. Aa, Aa, Aa.
• C. Aa, Aa, aa.
• D. AA, Aa, aa.
• E. None of the above.

The following pedigree is for the ABO blood type group, which is an example of autosomal inheritance. Using the I^A, I^B, i for the alleles, fill in the top half of each box/circle with the genotype. Also, fill in the bottom half of each box/circle with the phenotype (A, B, AB, or O blood type). If it is impossible to know for certain a specific allele in the genotype, then place a '?' as a placeholder to represent the allele that is in question.

Okay, everyone. The following pedigree is for the ABO blood type group, which is an example of autosomal inheritance. Using the, excuse me, the a, b, and I alleles, fill in the top half of each box or circle with the genotype. Okay. Also, fill in the bottom half of each box or circle with the phenotype as A, B, AB, or O blood type. If it is impossible to know for certain a specific allele in the genotype, then place a question mark as a placeholder to represent the allele that is in question. Okay. This is a big problem. Don't get overwhelmed by this. We have all the information to be able to answer this question. And just take your time when you do these types of questions. Okay? Alright. So we're going to be talking about blood type groups. So what your blood type is in this particular family, and the alleles that we are going to have are the a allele, the b allele, and the I allele. Remember that a and b are codominant, meaning that when they are together they're both expressed. And remember that the little I allele is recessive. So the a and b are codominant; the little I is recessive. And you can have type A blood, B blood, AB blood, or O blood. Okay. So, first off, let's just start with the parents. I'm going to start with these parents right here. So I can see that their children are type O. These two children, their son and their daughter are type O, which is homozygous recessive. But they tell us that these two parents are type A blood, which means that these parents must have the a allele because they are type A, but they must also have the recessive allele because they have type O children. So this must be their genotype here. Now, can we figure out their son's genotype? Well, their son could have an aa genotype. He could have ii genotype. He could have ai genotype. So we don't know quite yet. Let's see if we can figure out from his children. But first, I'm going to do the other side of the pedigree. So I'm going to do over here, this mother and father, and their children. Okay. So we can see that the mother is type O. We don't know anything about the dad, but we can see that his son is type A. So the mother must have given her recessive allele, and the father must have given his a allele. Okay. So now, is he type A blood? No. Realize that his daughter is type B, and the mother must have given her the recessive allele, which means the father must have given her the b allele. So this father is actually type AB blood. Okay. So now, can we figure out their other daughter right here? Again, not yet. We're going to have to look at their children. Okay. So, it's important to note that this male had children with this female, and these are their children below. Okay. So we know that the son, one of the sons, the son in the middle right here, is type O. There's only one genotype for type O, which is homozygous recessive. So we can immediately write in his genotype, homozygous recessive. Now they tell us another interesting thing is this individual right here, this son is type AB. There's only one genotype for type AB as well. So this son must have an a allele and a b allele. Okay. So these parents were able to have a type O child and a type AB child. So let's that means that one of them has to be type A, and one of them has to be type B. So what is the father? Well, remember that his parents are both type A, so he could not have given the b allele. So this father must be type A, and he is heterozygous with 1 a allele and 1 recessive I allele. But remember, they had a type AB son, so that means that the mother must be type B. So she's going to be type B, but because she had a homozygous recessive son, she must be a heterozygote as well. Okay. So that means that this individual is type A, this one is type B. Okay. So now let's figure out for the daughter, the one left in green, what is her genotype? Well, she's type A blood, So that means that the father must have given the a allele, and that means the mother must have given her recessive little I allele. Okay. So now we've figured out that family. Let's figure out this one right here. This woman, I'm going to highlight her in yellow, she is type AB, meaning that she only has one genotype. So she's going to have 1 a allele and 1 b allele. Now let's figure out their children. Both the father and the mother are type AB. They have a type A son. What is his genotype going to be? Well, he must have gotten 1 a allele from the dad and 1 a allele from the mom. Now we have a type AB daughter, again, only one genotype. And then we have a type B son. Remember that the father must have given a b allele, and the mother must have given a b allele because these two parents do not have the recessive allele, so they cannot give it. Okay. So we figured out that family. Let's move over to this family here, and we're almost done. Okay. So we have a type A mother, a type B father. Now, the key thing to see here is that they had a homozygous recessive type O daughter. So that means that the mother must have given a recessive allele, and the father must have given a recessive allele. So the father must be type B with 1 b allele and one recessive allele. Okay. So we figured that out. Now what about the son? This son is type A. So that means that this son must have gotten an a allele from the mother and the recessive I allele from the dad. Okay. Last one, super easy because this daughter can only have one genotype, and that is that she got the a allele from her mother and the b allele from her father. And, everyone, that is every single person in this pedigree, and we figured out how all of these different children got their blood types. Okay, everyone. Let's move on to our next video.

Here’s what students ask on this topic:

What is autosomal inheritance and how does it differ from sex-linked inheritance?

Autosomal inheritance refers to the transmission of traits or disorders through non-sex chromosomes, known as autosomes. Humans have 22 pairs of autosomes and one pair of sex chromosomes. Autosomal inheritance can be either dominant or recessive. In contrast, sex-linked inheritance involves genes located on the sex chromosomes (X and Y). Traits or disorders linked to the X chromosome are more common, as the Y chromosome carries fewer genes. In autosomal inheritance, both males and females are equally likely to inherit the trait, whereas in sex-linked inheritance, the pattern can differ between genders due to the presence of one or two X chromosomes.

What are the key differences between autosomal dominant and autosomal recessive disorders?

Autosomal dominant disorders require only one dominant allele for the trait or disorder to be expressed. This means that individuals with either a homozygous dominant (AA) or heterozygous (Aa) genotype will exhibit the disorder. These disorders typically appear in every generation. Examples include polydactyly. On the other hand, autosomal recessive disorders require two recessive alleles (aa) for the trait or disorder to be expressed. Individuals with a heterozygous genotype (Aa) are carriers but do not show symptoms. These disorders often skip generations. An example is cystic fibrosis.

How can pedigrees be used to distinguish between autosomal dominant and autosomal recessive disorders?

Pedigrees are family trees that track the inheritance of traits or disorders through generations. In autosomal dominant disorders, affected individuals appear in every generation, and at least one parent of an affected individual is also affected. In contrast, autosomal recessive disorders often skip generations, and affected individuals may have parents who are carriers but do not show symptoms. By analyzing the presence or absence of the disorder in each generation and the genotypes of family members, one can determine whether a disorder is autosomal dominant or recessive.

What are some examples of autosomal dominant and autosomal recessive disorders?

Examples of autosomal dominant disorders include polydactyly, where individuals have extra fingers or toes, and Huntington's disease, a neurodegenerative disorder. These disorders require only one dominant allele to be expressed. Examples of autosomal recessive disorders include cystic fibrosis, which affects the respiratory and digestive systems, and sickle cell anemia, which affects the shape of red blood cells. These disorders require two recessive alleles to be expressed, meaning both parents must be carriers or affected for the disorder to appear in their offspring.

Why do autosomal recessive disorders often skip generations?

Autosomal recessive disorders often skip generations because they require two recessive alleles (aa) for the disorder to be expressed. Individuals with only one recessive allele (Aa) are carriers and do not show symptoms. If two carriers have children, there is a 25% chance that their child will inherit both recessive alleles and express the disorder. However, if carriers do not have children with another carrier, the disorder may not appear in the next generation, leading to the appearance of skipping generations.