ANSC 221 (Exam 3): G8-Pedigree Analysis

What is the purpose of pedigree analysis?

To determine how traits are inherited in human families and predict possible genotypes and phenotypes of future offspring.

What symbols indicate an affected individual in a pedigree?

An affected individual is represented by a filled symbol, indicating the phenotype is expressed.

What is the inheritance pattern of an autosomal dominant trait?

An affected individual typically has an affected parent, and the trait does not skip generations.

What is an example of an autosomal recessive trait?

Inability to taste PTC (a chemical found in vegetables).

How do you calculate the probability of a child having both a widow's peak and inability to taste PTC?

Multiply the probabilities of each trait: (¾ for widow's peak) x (¼ for inability to taste PTC) = 18.75% (or 3/16).

What are the characteristics of an autosomal recessive trait?

Unaffected parents can have affected offspring, and the trait often skips generations.

What is the inheritance pattern of X-linked recessive traits?

Traits may skip generations, are never passed from father to son, and males are affected more frequently than females.

What is an example of an X-linked dominant trait?

Hypophosphatemia.

What are the characteristics of X-linked dominant traits?

The trait does not skip generations, affected sons always have affected mothers, and all daughters of an affected male are affected.

What is the significance of the alleles M and m in the context of myopia?

They control the expression of myopia, which needs to be analyzed in a pedigree.

What is the role of pedigree analysis in genetics?

It helps interpret symbols and conventions, predict genotypes and phenotypes, and distinguish between inheritance patterns.

Purpose of pedigree analysis

Understand inheritance patterns in families; predict genotypes and phenotypes.

Why it's used in humans

Ethical limitations prevent experimental matings; relies on family history.

Basic symbols in pedigree analysis

☐ = male, ○ = female, ⦿ = affected individual, ☐○ = mating, ☐☐☐ = offspring in birth order.

Advanced symbols in pedigree analysis

◇ = sex unknown, ☐= consanguineous parents, ☐= twins (identical/fraternal), ☐= deceased, ☐= heterozygous carriers, Roman numerals = generations.

Autosomal Dominant Traits

Trait does not skip generations; affected individuals have affected parent; males and females equally affected; unaffected = homozygous recessive.

Example of Autosomal Dominant Trait

Widow's peak.

Probability example for Autosomal Dominant Traits

Ww × Ww → Prob(Ww or WW) = ¾ = 75%.

Autosomal Recessive Traits

Trait can skip generations; affected individuals = homozygous recessive; unaffected parents = carriers; males and females equally affected.

Examples of Autosomal Recessive Traits

PTC tasting, Albinism.

Probability example for Autosomal Recessive Traits

Tt × Tt → Prob(tt) = ¼ = 25%.

Two-Gene Pedigree Analysis

Combined traits: Widow's peak (dominant) + inability to taste PTC (recessive).

Probability example for Two-Gene Pedigree Analysis

WwTt × WwTt → Prob[(WW or Ww) and (tt)] = 3/16 = 18.75%.

X-linked Recessive Traits

Trait often skips generations; males more frequently affected (hemizygous); fathers never pass trait to sons; carrier mothers → 50% of sons affected.

Example of X-linked Recessive Trait

Red-green color blindness.

X-linked Dominant Traits

Trait does not skip generations; males and females equally affected; affected fathers → all daughters affected, no sons; affected mothers → 50% of offspring affected.

Example of X-linked Dominant Trait

Hypophosphatemia.

Trait Classification Logic

Diagnostic questions: Do all affected individuals have affected parents? Are males more affected? Do affected fathers pass trait to all daughters but no sons?

Classification outcomes

Use answers to classify as autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive, or Y-linked.