Question

Using a pedigree, show an autosomal recessive disorder pattern and an autosomal dominant disorder pattern. (pages \(474-75\) )

Short answer

An autosomal recessive disorder pattern can be represented in a pedigree as follows: ``` I II III 1 2 1 2 3 4 1 2 3 4 5 6 □□ □□ □□ □□ □ □□ □□□ □ ``` Here, individuals II-4 and III-6 have the autosomal recessive disorder represented by a shaded symbol. An autosomal dominant disorder pattern can be represented in a pedigree as follows: ``` I II III 1 2 1 2 3 4 1 2 3 4 5 6 □□ □ ■ □ □ ■ □ □ □ □ ■ ``` In this pedigree, individuals II-2, III-1, and III-6 have the autosomal dominant disorder represented by a shaded symbol.

Step-by-step solution

Understand autosomal recessive inheritance

Autosomal recessive inheritance is when two copies of an abnormal gene must be present in the offspring for the disorder to manifest. This means that individuals carrying only one copy of the abnormal gene (heterozygous carriers) do not exhibit symptoms or signs of the disease. Step 2: Construct a pedigree for an autosomal recessive disorder

Construct a pedigree for an autosomal recessive disorder

To show an autosomal recessive disorder pattern using a pedigree, we will use the following symbols: squares for males, circles for females, and a shaded shape representing individuals with the disorder. The generations are labeled using Roman numerals (I, II, III, etc.), and the individuals within each generation are labeled using Arabic numerals (1, 2, 3, etc.). An example of a pedigree for an autosomal recessive disorder is as follows: ``` I II III 1 2 1 2 3 4 1 2 3 4 5 6 □□ □□ □□ □□ □ □□ □□□ □ ``` In this pedigree, individuals II-4 and III-6 have the autosomal recessive disorder represented by a shaded symbol. Step 3: Understand autosomal dominant inheritance

Understand autosomal dominant inheritance

Autosomal dominant inheritance is when only one copy of an abnormal gene is required for the disorder to manifest in the offspring. This means that individuals can inherit the abnormal gene from either parent, and a parent with the disorder has a 50% chance of passing the gene to each of their children. Step 4: Construct a pedigree for an autosomal dominant disorder

Construct a pedigree for an autosomal dominant disorder

To show an autosomal dominant disorder pattern using a pedigree, we will use the same symbols as in the autosomal recessive example: squares for males, circles for females, and a shaded shape representing individuals with the disorder. An example of a pedigree for an autosomal dominant disorder is as follows: ``` I II III 1 2 1 2 3 4 1 2 3 4 5 6 □□ □ ■ □ □ ■ □ □ □ □ ■ ``` In this pedigree, individuals II-2, III-1, and III-6 have the autosomal dominant disorder represented by a shaded symbol.

Key concepts

Autosomal Recessive Disorders

Autosomal recessive disorders occur when an individual inherits two copies of an abnormal gene. This means that both parents must carry at least one copy of the flawed gene, making them carriers. However, the parents might not show any symptoms because they are heterozygous, meaning they have one normal gene and one abnormal gene. For a child to be affected by an autosomal recessive disorder, they must inherit the abnormal gene from both parents.
If both parents are carriers, there is a 25% chance with each pregnancy that the child will inherit the disorder. The chance of the child being a carrier like their parents is 50%, and lastly, there is a 25% chance the child will inherit two normal genes. Examples of autosomal recessive disorders include cystic fibrosis and sickle cell anemia.

• Requires two abnormal genes for disorder manifestation
• Carriers are asymptomatic
• 25% chance of affected child if both parents are carriers

Analyzing pedigrees helps identify autosomal recessive inheritance by finding patterns where affected individuals tend to only appear when their parents are carriers, often skipping generations.

Autosomal Dominant Disorders

In contrast to autosomal recessive disorders, autosomal dominant disorders require only one copy of an abnormal gene for the disorder to manifest. This means an individual can inherit the condition from just one affected parent. If a parent has an autosomal dominant disorder, each child has a 50% chance of inheriting the disorder.
Autosomal dominant conditions do not usually skip generations because the presence of a single abnormal gene is sufficient to cause the disorder. Because of this, it's more common to see every generation affected in a pedigree, assuming the gene is inherited. Conditions such as Huntington's disease and Marfan syndrome follow this inheritance pattern.

• One abnormal gene causes disorder manifestation
• 50% chance of passing the disorder from an affected parent to child
• Tends to affect every generation without skipping

Pedigree analysis can highlight these patterns by showing a clear vertical transmission of the disorder, with affected individuals in each generation.

Genetic Inheritance Patterns

Understanding genetic inheritance patterns is crucial in predicting and recognizing genetic disorders. A pedigree is often used as a visual tool to study these patterns. It helps trace how traits or disorders are passed down from generation to generation.
Pedigrees use standardized symbols: squares for males, circles for females, and shading to indicate individuals who express the trait or disorder. The pedigree layout includes notation to represent each generation sequentially. This makes it easier to identify inheritance patterns, whether they are dominant, recessive, or even sex-linked.
With autosomal recessive disorders, the pattern typically shows affected individuals arising from parents who do not express the disorder themselves. In contrast, autosomal dominant disorders will show affected individuals with at least one parent who also has the disorder, reflecting the disorder’s ability to appear in each generation.

• Pedigrees map out inheritance across generations
• Consistent symbols are used to indicate gender and disorder presence
• Helps distinguish between dominant and recessive patterns

By using pedigrees, researchers and medical professionals can predict genetic risks and advise families on health decisions and genetic counseling.