Pedigree Analysis: Identifying Linked Markers

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Explain how to determine which marker allele is most likely linked to the disease phenotype in the pedigree. How would you identify the critical individuals and analyze their marker alleles?

To determine the most closely linked marker, look for the marker allele that consistently segregates with the disease across affected individuals without recombination events. Identify individuals where recombination might have separated the marker from the disease allele, then analyze which marker has the fewest such instances.

Describe the criteria you would use to compare the genetic distances between marker pairs (A-B and B-C) using pedigree data. How do crossover frequencies relate to genetic distance?

Compare the recombination frequencies between each marker pair. Higher recombination frequency indicates a greater genetic distance. Identify individuals in the pedigree where crossovers between the marker pairs are evident by comparing allele inheritance patterns and correlate this to genetic distance.

If a new individual expressing the disease phenotype also possesses the C2 marker allele, how does this influence your deduction regarding linkage? Explain how this observation either strengthens or weakens the inferred linkage between the phenotype and that marker.

The presence of the C2 allele in another affected individual strengthens the linkage inference, because it provides further evidence that this allele is inherited along with the disease. This additional data point increases confidence in the association between the marker and the disease gene, assuming other factors remain constant.

How would the appearance of the disease phenotype in an individual lacking the A1 allele affect your analysis of the pedigree? Explain the possible reasons for this discrepancy and its implication to the linkage analysis.

Appearance of the disease without the A1 marker would suggest a recombination event between the A marker and the disease locus in that individual's lineage, indicating that the A marker is not perfectly linked to the disease gene. It could also be explained by genetic heterogeneity, de novo mutation, or phenocopy. Signup and view all the answers

Explain the concept of a haplotype and its relevance to linkage analysis using the given pedigree. How do specific combinations of alleles from markers A, B, and C form a haplotype, and how can analyzing haplotype inheritance patterns in a pedigree improve the precision of locating a disease gene?

A haplotype is a set of DNA variations, or polymorphisms, that tend to be inherited together. In this pedigree, a haplotype is formed by the combination of A, B, and C alleles on a single chromosome. Analyzing haplotype inheritance can help narrow down the location of a disease gene by identifying specific allele combinations that consistently segregate with the disease phenotype, more precisely mapping the disease gene. Signup and view all the answers

Flashcards

Pedigree Analysis

A diagram representing family relationships used to study inheritance.

Autosomal Dominant Trait

A genetic trait expressed if at least one dominant allele is present.

Squares and Circles in Pedigree

Squares represent males; circles represent females in the pedigree chart.

Disease Phenotype

The observable characteristics indicating the presence of a disease trait.

Signup and view all the flashcards

Genetic Marker

A specific sequence of DNA used to identify a gene associated with a trait.

Signup and view all the flashcards

Study Notes

Pedigree Analysis

Three-generation pedigree shows an autosomal dominant trait.
Squares represent males, circles represent females.
Open symbols indicate normal phenotype, solid symbols indicate disease phenotype.
Alleles at three marker loci (A, B, C) are shown.

Marker Loci

Each individual has specific allele combinations for markers A, B, and C.
- e.g., individual III-1 has A1, B2, C2
The number next to an allele (e.g., A1 2) indicates the number of times the specific allele is observed in the pedigree.

Question 1: Most Linked Marker

Determine which marker (A1, A2, A3, B1, B2, B3, B4, C2, or C4) is most closely linked to the disease phenotype.
The linkage is determined by the observation of how often the marker allele is present in individuals with the disease phenotype in the pedigree.

Question 2: Shortest Distance Between Markers

Determine if the distance between markers A-B or B-C is shorter.
The distance between markers is determined by observing how frequently the alleles from different loci are observed together.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Analyze a three-generation pedigree chart to determine the marker locus most closely linked to an autosomal dominant disease. Evaluate allele combinations and frequencies to infer genetic relationships.