PEDIGREES Chapter 14 Pedigree A pedigree is a

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PEDIGREES Chapter 14

PEDIGREES Chapter 14

Pedigree • A pedigree is a chart for tracing genes in a family •

Pedigree • A pedigree is a chart for tracing genes in a family • They can be used to study the transmission of a hereditary condition • Phenotypes are used to infer genotypes on a pedigree

Symbols Used in a Pedigree ¢ ¢ ¢ Normal male Affected male Normal female

Symbols Used in a Pedigree ¢ ¢ ¢ Normal male Affected male Normal female Affected female A marriage with five children, two daughters and three sons. The middleaged son is affected by the condition. Vertical Lines- offspring Marriage/Mating Oldest child Youngest child

Organizing the Pedigree • Generations are identified by Roman numerals I II IV

Organizing the Pedigree • Generations are identified by Roman numerals I II IV

Organizing the Pedigree • Individuals in each generation are identified by numbers. • Therefore

Organizing the Pedigree • Individuals in each generation are identified by numbers. • Therefore the affected individuals are II 3, IV 2 and IV 3 I II IV

Patterns of Inheritance v Basic patterns of inheritance vautosomal, recessive vautosomal, dominant v. X-linked,

Patterns of Inheritance v Basic patterns of inheritance vautosomal, recessive vautosomal, dominant v. X-linked, recessive v. X-linked, dominant (very rare)

Autosomal Recessive Traits • Trait is rare in pedigree • Trait often skips generations

Autosomal Recessive Traits • Trait is rare in pedigree • Trait often skips generations • hidden in heterozygous carriers (sometimes shown half shaded) • Trait affects males and females equally

Autosomal Recessive Traits v Most common ones • Cystic fibrosis • Sickle cell anemia

Autosomal Recessive Traits v Most common ones • Cystic fibrosis • Sickle cell anemia • Phenylketonuria (PKU) • Tay-Sachs disease v For each of these, over dominance (heterozygote superiority) has been suggested as a factor in maintaining the disease alleles at high frequency in some populations

Autosomal Recessive Trait • If you ever see this situation in the pedigree (two

Autosomal Recessive Trait • If you ever see this situation in the pedigree (two unaffected parents have an affected child) then the trait MUST be recessive! • The parents are heterozygous.

Autosomal Dominant Trait • Trait is common in the pedigree • Trait is found

Autosomal Dominant Trait • Trait is common in the pedigree • Trait is found in every generation • Affected individuals transmit the trait to ~1/2 of their children (regardless of sex)

X-linked Recessive Trait • Trait is rare in pedigree • Trait skips generations •

X-linked Recessive Trait • Trait is rare in pedigree • Trait skips generations • Affected fathers DO NOT pass to their sons, • Males are more often affected than females

X-linked Recessive Trait • ex. Hemophilia in European royalty

X-linked Recessive Trait • ex. Hemophilia in European royalty

Steps to Determine Inheritance Pattern of a Trait Step 1: Determine whether it’s dominant

Steps to Determine Inheritance Pattern of a Trait Step 1: Determine whether it’s dominant or recessive. • Does it skip generations? YES= recessive NO= dominant. Step 2. Determine whether is is autosomal or x-linked. • Does it affect one gender more than the other? YES= X-linked NO= autosomal

What Inheritance Pattern Does this Trait Follow?

What Inheritance Pattern Does this Trait Follow?

 • What is the inheritance pattern? • What is the genotype of III-1,

• What is the inheritance pattern? • What is the genotype of III-1, III-2, and II-3? • What are the odds that IV-5 would have an affected son?

Pedigree Analysis in Real Life • Remember: • dominant traits may be rare in

Pedigree Analysis in Real Life • Remember: • dominant traits may be rare in population • recessive traits may be common in population • alleles may come into the pedigree from 2 sources • mutation happens • often traits are more complex • affected by environment & other genes