Patterns of Inheritance

Some inherited diseases, including LCA, may be caused by mutations in a single gene. Pedigrees can be used to determine the patterns of inheritance for these diseases. In a 1998 study, scientists analyzed a series of pedigrees showing the family histories of LCA patients. Some of their pedigrees are shown in the following figures. Squares represent males, circles represent females, and shading indicates that an individual has LCA. Based only on the pedigree in Figure 1, can you determine whether LCA is or isn’t inherited according to an autosomal dominant, autosomal recessive, or X-linked recessive pattern? E

• This is autosomal dominant

• This is autosomal recessive

• This is X-linked recessive pattern

• You can’t rule out any of these inheritance patterns based only on this pedigree

Based on the pedigrees in Figure 2, can you determine whether LCA is or isn’t inherited according to an autosomal dominant, autosomal recessive, or X-linked recessive pattern? Explain your answer.

• You can determine LCA isn’t inherited according to an autosomal dominant pattern.

• You can determine LCA isn’t inherited according to an autosomal recessive pattern.

• You can determine LCA isn’t inherited according to an X-linked pattern.

• You can’t rule out any of these inheritance patterns based only on this pedigree

Based on the pedigrees in Figure 3, is LCA inherited according to an autosomal dominant, autosomal recessive, or X-linked recessive pattern?

• autosomal dominant

• autosomal recessive

• X-linked recessive

• It is not possible to determine the inheritance pattern

Recall that a person typically has two copies, called alleles, of every gene. One or both of these alleles may be mutated in certain individuals. Use what you know about LCA’s inheritance pattern to write the genotypes for Family #4 in Figure 3, using L to represent an unmutated allele and l to represent a mutant, disease-causing allele for the LCA-related gene. What are the possible genotypes of both parents in this family?

• Mother - LL Father - LL

• Mother - Ll Father - Ll

• Mother - ll Father - ll

• Mother - LL Father - ll

• Mother - LL Father - Ll

Recall that a person typically has two copies, called alleles, of every gene. One or both of these alleles may be mutated in certain individuals. Use what you know about LCA’s inheritance pattern to write the genotypes for Family #4 in Figure 3, using L to represent an unmutated allele and l to represent a mutant, disease-causing allele for the LCA-related gene. What are the possible genotypes of the female child without LCA? ?

• Li

• LL

• ll

• Ll or LL

• ll or LL

Although Molly has LCA, her parents do not. Which of the following would represent a pedigree for Molly and her parents using the same style as in the previous pedigrees.

• 
• 
• 
• all of the above

• none of the above

Although Molly has LCA, her parents do not. Draw a pedigree for Molly and her parents using the same style as in the previous pedigrees. What are the genotypes for each person using L and l as before.

• Molly - ll

• Molly - Ll

• Molly - LL

• Father and Mother - ll

• Father and Mother - Ll