Pedigree Analysis Quiz Questions With Answers

Pedigree A suggests a recessive inheritance pattern because the trait skips a generation. In recessive inheritance, individuals who do not show the trait can still carry the gene and pass it on. It can appear in offspring only if both parents are carriers of the recessive allele. In this case, neither parent expresses the trait, but one child does, indicating the trait is recessive. It could also be X-linked recessive, but without additional information, autosomal recessive is a reasonable conclusion.

In this pedigree, the trait appears to skip generations, and both males and females are affected with roughly equal frequency. These observations suggest an autosomal recessive inheritance pattern.

Here's why:

Autosomal: The trait appears in both sexes, indicating it's not linked to a sex chromosome.

Recessive: The trait skips generations, meaning unaffected individuals can have affected offspring. This is a hallmark of recessive inheritance, where both parents must carry the recessive allele for the trait to appear in their child.

The information about marriage partners from outside the family further supports this conclusion, as it suggests that the trait is relatively rare in the general population, which is often the case with recessive conditions.

In Pedigree C, neither parent expresses the trait, but both a son and a daughter do. This suggests an autosomal recessive inheritance pattern, where both parents are carriers of the recessive allele but do not show the trait themselves. The children express the trait because they inherit two copies of the recessive allele, one from each parent. Autosomal recessive traits can skip generations if the carriers do not express the trait but pass it on to their offspring.

Individual #7 can have the genotype Aa. This is because the affected individuals in the pedigree are shown as shaded, indicating that they have the dominant trait. Since individual #7 is affected, they must have at least one copy of the dominant allele, which is represented by "A". However, since none of the marriage partners from outside these two families are heterozygous for the trait, individual #7 cannot have the genotype AA. Therefore, the only possible genotype for individual #7 is Aa.

Individual #8 can have the genotype Aa. This is because the trait is dominant, and individual #8 is affected, which means they must have at least one dominant allele. Since none of the marriage partners from outside the families are heterozygous for the trait, it is likely that individual #8 inherited the dominant allele from one of their parents who is affected. Therefore, individual #8 can have the genotype Aa.

Pedigree D suggests a dominant inheritance pattern because the trait appears in every generation, which is characteristic of dominant inheritance. In dominant inheritance, only one copy of the mutated gene is necessary for the trait to be expressed. The fact that the trait is passed down to offspring in each generation, and both males and females are affected, supports the conclusion that the trait follows a dominant inheritance pattern. Additionally, the trait could be X-linked dominant, as both daughters express the trait.

Individual #2 can have a genotype of Aa because they are affected by the trait, which means they must have at least one copy of the dominant allele A. However, since they are affected, they must also have a copy of the recessive allele a. Therefore, their genotype can be Aa.

Based on the information provided, the affected individuals in the pedigree are shown shaded. Since none of the marriage partners from outside these two families are heterozygous for the trait, it can be inferred that the trait is likely inherited in an autosomal recessive manner. Individual #1 is not affected, so they could either be homozygous dominant (AA) or heterozygous (Aa) for the trait. Since the trait is not shown in either of their parents, it is more likely that individual #1 is heterozygous (Aa) for the trait.

Huntington's Disease, a well-known autosomal dominant disorder, follows a pattern where only one copy of the altered gene is sufficient to cause the disease. The trait appears in every generation, and both males and females can be affected. This pattern is clearly demonstrated in the pedigree, where affected individuals have at least one affected parent.

If two unaffected individuals (neither of them has the trait) have a child with the trait, the most likely mode of inheritance for this trait is autosomal recessive. 



In autosomal recessive inheritance, the trait is typically "hidden" or not expressed in carriers (heterozygous individuals), but it can be expressed when two carriers have a child together, and both pass on the recessive allele for the trait. This means that two unaffected parents can have a child with the trait if they both carry a single copy of the recessive allele and pass it on to their child. This scenario is characteristic of autosomal recessive inheritance.

Individual #5 is affected, meaning they have at least one copy of the dominant allele. Since they are not homozygous dominant (as marriage partners outside the family are not heterozygous), the only possible genotype for individual #5 is Aa, having one dominant allele and one recessive allele.

In this pedigree, the trait is dominant because the affected female (#4) is heterozygous (XBXb) and has a son who expresses the trait. The father (#3) is XbY, meaning he passed the Y chromosome to his son, but the son still inherits the dominant allele (XB) from his mother. This confirms that the inheritance is dominant. Dominant traits are typically expressed even if only one allele is present, which is the case here.

The pedigree shows affected individuals in multiple generations, including siblings with unaffected parents, which is typical of an autosomal recessive inheritance pattern. Both males and females are affected, suggesting the gene is not sex-linked. The presence of heterozygous carriers (indicated) and affected homozygous individuals supports autosomal recessive inheritance.

Individual #3 must have the genotype AA because the trait is dominant and both of their parents are affected (shaded), meaning they have at least one copy of the dominant allele. Since none of the marriage partners from outside the families are heterozygous for the trait, it can be inferred that both parents of individual #3 are homozygous dominant (AA).

In Pedigree E, the trait appears to follow an autosomal recessive inheritance pattern. This is because it can skip generations, meaning the trait may not appear in each generation, but can still be passed on by carriers. Both males and females are equally likely to inherit the trait, which is a hallmark of autosomal recessive inheritance. The trait is typically expressed in individuals who inherit two copies of the recessive allele, one from each parent.

The trait appears to skip generations in family I and family III, with equal numbers of affected males and females. This suggests autosomal recessive inheritance. For recessive traits, both parents must be carriers (heterozygous) for the trait to be expressed in their offspring, which may result in the trait being passed down through generations without being expressed in each generation.

Based on the information provided, we know that the trait is recessive since none of the marriage partners from outside these two families are heterozygous for the trait. Individual #10 is affected, which means they must have two copies of the recessive allele. Therefore, the genotype of individual #10 can only be aa.

In the pedigree chart, both males and females are affected in multiple generations, and the condition does not skip generations consistently or show a clear pattern linked to one sex. Additionally:

Affected individuals appear in both sexes roughly equally

An affected individual can have unaffected parents, suggesting recessive traits in some cases

These features are characteristic of an autosomal inheritance pattern, rather than sex-linked, which typically affects one sex (often males) more frequently.

The pedigree indicates that only females are carriers of the trait, and more males than females are affected. This suggests sex-linked recessive inheritance. In such a pattern, males are typically affected because they have only one X chromosome, while females can be carriers if they have one affected X chromosome and one unaffected X chromosome.

Individual #6 must have the genotype aa because the trait is dominant and both of their parents are affected, meaning they must carry at least one copy of the dominant allele. Since the trait is not present in any of the marriage partners from outside the two families, it can be concluded that the trait is not inherited from any outside source and must be inherited from the affected parents.

In this pedigree, the affected father passes the trait to all his daughters, making them affected, which is characteristic of X-linked dominant inheritance. He does not pass the affected allele to his sons, who remain unaffected, also consistent with this pattern. While autosomal dominant with heterozygous parents could theoretically produce this outcome in a small family, the direct transmission from an affected father to all daughters strongly suggests an X-linked dominant mode of inheritance. The observed pattern effectively rules out autosomal recessive and X-linked recessive inheritance.

Autosomal recessive inheritance is suggested in this pedigree, as two unaffected parents have a child who expresses the trait. This scenario is typical of autosomal recessive inheritance, where both parents are carriers of the recessive allele but do not show the trait themselves. The trait is expressed in the child when they inherit two copies of the recessive allele, one from each parent. This pattern can also apply to other types of inheritance, but autosomal recessive fits the description here.

Based on the information given, we can determine that the trait being referred to is dominant. Since none of the marriage partners from outside these two families are heterozygous for the trait, it implies that both parents of individual #9 are affected. Therefore, individual #9 can have either the genotype AA or Aa.

Individual #11 is the child of two affected individuals, who are both shaded in the pedigree. Since the trait is shown as shaded, it is likely a dominant trait. Both affected individuals could either be heterozygous (Aa) or homozygous dominant (AA). Therefore, individual #11 could have either the genotype aa or AA.