1. Pedigrees: Tracking Inheritance
Section 5.3

2. Pedigrees Tracking Inheritance
Learning Goal: To learn how pedigrees show the inheritance of a trait among family members.
Success Criteria:
explain the symbols used in pedigrees
use pedigrees too determine genotype and phenotypes of family members
use pedigrees to predict whether a trait is recessive or dominant

3. Pedigrees
Pedigree: a chart that traces the inheritance of a certain trait among members of a family
composed of symbols identifying sex, relationships between individuals and the presence or absence of a trait
Squares represent males and circles represent females. Individuals who express a trait are shown in a shaded circle or square. Mating between two individuals is shown by a horizontal line, and children are connected to their parents with vertical lines.

4. Pedigrees Cont’d…
squares represent males and circles represent females
individuals who express a trait are shown by a shaded circle or square
mating between two individuals is shown by a horizontal line
children are connected to their parents with vertical lines
Ex. Three generation pedigree for freckles (dominant trait)

5. Pedigrees Cont’d… each generation is identified by Roman numerals
Arabic numbers symbolize individuals within a given generation
birth order within each group of offspring is drawn from left to right, from oldest to youngest
Ex. Three generation pedigree for freckles (dominant trait)

6. Interpreting Pedigree Charts
Sample Problem 1: Determining Genotypes of Individuals
Marfan syndrome is a genetic disorder that affects the body’s connective tissue. When the dominant allele (M) is expressed, an individual will have Marfan syndrome. People with no defect in the Marfan allele are homozygous recessive (mm). Use the pedigree chart to determine the genotypes of all individuals, if possible.
Figuring out genotypes from phenotypes on a pedigree chart requires you to use a process of elimination. You can often determine which genotypes are possible and which are not.
Individuals with the syndrome are typically very tall, with disproportionately long limbs and fingers, and sometimes have problems with their hearts and eyes.

7. Interpreting Pedigree Charts Cont’d…
Sample Problem 2: Determining the Modes of Inheritance
Individuals with albinism have a defect in an enzyme that is involved in the production of melanin, a pigment normally found in the skin. These individuals have little or no pigment in their skin, hair, and eyes. The characteristic is governed by only two alleles: the normal allele and the albinism allele. Analyze the pedigree chart to determine whether the albinism allele is a dominant or a recessive allele. Then determine the genotypes of each individual.

8. Practice Problems
Phenylketonuria (PKU) is a genetic disorder caused by a recessive allele. Individuals with PKU accumulate phenylalanine in their body. High amounts of phenylalanine lead to delayed mental development. This pedigree chart shows the inheritance of the defective PKU allele in one family.
How many generations are shown in the pedigree chart?
Determine the genotypes of the individuals.

9. Practice Problems Cont’d…
Not all humans react strongly to poison ivy. This trait is thought to be controlled by a single allele. The following pedigree shows the inheritance of sensitivity to poison ivy in one family.
Analyze the pedigree chart and determine whether the disorder is inherited as a result of a dominant or a recessive trait.
Determine the genotype for each individual if possible.

10. Homework: Complete lab activity “Constructing a Human Pedigree”
Due Friday