Pedigree Analysis

Exam Information

• Exam #3 Details:

  • Date: Friday, November 7th

  • Duration: 50 minutes

  • Format: In-class

  • Number of Questions: 45

  • Rules:

  • You may navigate back and forth between questions.

  • Must submit all answers once.

  • Return all scratch paper upon leaving the exam.

  • Keep your browser focused on the Canvas exam page throughout the test. Opening other tabs, windows, or applications may result in a violation of academic integrity.

• Exam Review Session:

  • Course: ASL 150

  • Date: Wednesday, November 5th

  • Time: 5-6 PM

Pedigree Analysis Overview

Purpose and Learning Objectives

• Main Purpose:

  • To determine how traits are inherited in human families and predict genotypes and phenotypes of a family.

• Learning Objectives:

  • Understand the purpose of pedigree analysis.

  • Interpret symbols and conventions used in pedigrees.

  • Use pedigree analysis to predict possible genotypes and phenotypes (diseases or disorders) of future offspring.

  • Distinguish between different types of inheritance patterns.

Pedigree Analysis Definition

• Definition:

  • Pedigree analysis is the study of inheritance patterns of traits in humans and animals.

• Function:

  • It allows for the prediction of possible genotypes and phenotypes in future offspring based on existing family history and tree information.

Characteristics of Pedigree Analysis

• Commonality:

  • More common in humans, as experimental matings are typically not ethical, resulting in limited offspring for study.

  • Relies on information gathered from family trees or pedigrees.

Symbols Used in Pedigree Analysis

• Male and Female Symbols:

  • Male (□), Female (○)

• Trait Representation:

  • Affected Male (■), Affected Female (●)

  • Unaffected Individuals (empty shapes)

  • Consanguineous (related) parents (connecting line between parental symbols)

  • Offspring: Placed in birth order from left to right, with first-born on the left.

  • Identical (monozygotic) twins denoted by connecting lines between same-sex symbols, while fraternal (dizygotic) twins are indicated with a bracket between two symbols where sex can differ.

  • Proband: The individual through whom the pedigree is being traced (indicated with an arrow).

  • Deceased Individuals: Marked with a slash through the respective symbol.

Different Types of Traits

Autosomal Dominant Traits

• Example Trait: Widow's peak

• Characteristics:

  • Affected individuals have at least one affected parent; the trait often does not skip generations.

  • If one parent is heterozygous, about 50% of their offspring will be affected.

  • Both males and females are equally likely to be affected.

• Probability Problem:

  • If two heterozygous individuals (Ww) have a child, the probabilities for the offspring inheriting a dominant allele for widow's peak are as follows:

  • $P(WW ext{ or } Ww) = rac{1}{4} + rac{1}{2} = rac{3}{4} = 75\%$

  • Gamete combinations:

  • Female: W w

  • Male: W w

  • Resulting offspring combinations:

  • WW, Ww, Ww, ww

Autosomal Recessive Traits

• Example Trait: Inability to taste PTC

• Characteristics:

  • Affected individuals can have unaffected parents, indicating that those parents are heterozygous carriers.

  • If both parents are heterozygous (Tt), the probability that their child will be unable to taste PTC is:

  • $P(tt) = rac{1}{2} imes rac{1}{2} = rac{1}{4} = 25\%$

• Gamete Combinations:

  • Female: T t

  • Male: T t

  • Resulting Offspring Combinations:

  • TT, Tt, Tt, tt

Pedigree Analysis with Two Genes

• Genetic Problem: What is the probability that a child will inherit a widow's peak and inability to taste PTC?

• Probability Calculation:

• $P[(WW ext{ or } Ww) ext{ and } (tt)] = rac{3}{4} imes rac{1}{4} = rac{3}{16} = 18.75\%$

X-linked Traits

X-linked Recessive Traits

• Example Trait: Red-green color-blindness

• Characteristics:

  • This trait can skip generations and is never passed from father to son.

  • Males are affected more frequently than females because they only need one copy of the mutant allele to exhibit the trait.

  • Approximately 50% of the sons from carrier mothers will be affected, while all daughters of an affected male and an unaffected female are carriers.

X-linked Dominant Traits

• Example Trait: Hypophosphatemia

• Characteristics:

  • This trait does not skip generations and males and females are equally affected.

  • Affected sons always have affected mothers, while all daughters of affected males are affected, but no sons.

  • Approximately 50% of the offspring of an affected mother will also be affected.

Distinguishing Traits Based on Inheritance Patterns

• Key Questions to Identify Type of Trait:

  • Do all affected individuals have an affected parent?

  • Do all affected males have an affected mother?

  • Does an affected father produce daughters who are all affected?

  • Do the traits predominantly affect males?

• Inheritance Type Summary:

  • If all affected sons of an affected father are also affected, the pattern suggests Autosomal Dominant.

  • If an affected father produces unaffected sons, the pattern suggests Autosomal Recessive.

  • If the trait affects more males than females, the pattern suggests X-linked Recessive or potentially Y-linked Trait.

Lesson Recap

• Key Skills Recap:

  • Understand the purpose of pedigree analysis.

  • Interpret symbols and conventions in pedigree analysis.

  • Use pedigree analysis to predict genotypes and phenotypes of a family.

  • Distinguish between different types of inheritance patterns.