Human Inheritance and Pedigrees

Determining Trait Type: Students must be able to determine whether a trait is dominant or recessive by analyzing the results of a Punnett square or a pedigree.
Genotype Identification: Utilize pedigrees to determine genotypes and rates of inheritance for autosomal dominant and autosomal recessive traits.
Pedigree Construction: Draw pedigrees to trace the inheritance of a trait across multiple generations of a family based on a provided scenario.

Limitations in Human Genetic Study: In humans, scientists are limited in their ability to track diseases due to specific factors: * Small sample sizes (humans produce relatively few offspring). * The requirement for multi-generational studies to observe inheritance patterns over time.
Definition of a Pedigree: A pedigree is a diagram listing the members and ancestral relationships in a family. It is a fundamental tool used in the study of human heredity.
Mendelian Inheritance in Humans: The inheritance of certain human traits is predictable based on Mendelian inheritance patterns, which are organized by the time frame of the study.

Standard Form and Purpose: Pedigrees use a standard form and specific symbols to represent family history. This history allows for: * The illustration of how a trait is inherited. * Estimation of genetic risk for family members. * Provision of genetic counseling for individuals at risk of having children with genetic disorders.
Symbols and Conventions: * Females: Designated by circles ( $\bigcirc$ ). * Males: Designated by squares ( $\square$ ). * Affected Individuals: Shaded circles and squares represent individuals who express the genetic trait of interest. * Unaffected Individuals: Unshaded circles and squares represent individuals who do not express the trait. * Unions: A horizontal line between a square and a circle represents a union, such as a marriage. * Offspring: Vertical lines extending downward from a union line represent the children of that union. * Generations: Specific individuals in a pedigree are identified by generation, which is numbered using Roman numerals (I, II, III, etc.) down the left side of the chart.

Definition: In an autosomal dominant disorder, a single copy of an allele causes the phenotype associated with the genetic disease.
Gain-of-Function Mutations: These are often referred to as gain-of-function mutations because the presence of a single mutant allele determines the phenotype.
Inheritance Requirements: * At least one parent with the disease is required to pass the trait along to offspring. * Typical Punnett Square Example ( $D$ = dominant affected, $d$ = recessive unaffected): * If one parent is heterozygous ( $Dd$ ) and the other is homozygous recessive ( $dd$ ): * Children: $50\%$ chance of ( $Dd$ ) (Affected), $50\%$ chance of ( $dd$ ) (Unaffected).

Definition: These mutations require two copies of the recessive allele for the phenotype to be expressed. As long as one copy of a functional gene is present, the individual usually exhibits the normal phenotype.
Loss-of-Function Mutations: These are often called loss-of-function mutations because the phenotype represents a lack of an ability to perform a specific function. * Example: Sickle-cell disease, where the body lacks the full ability to transport oxygen effectively.
Carrier Status: Unaffected parents can be "carriers" (heterozygous), meaning they do not show the trait but can pass the recessive allele to their children.
Inheritance Requirements: * Carrier parents ( $Nn \times Nn$ ) can give birth to a child with the disease ( $nn$ ). * Typical Punnett Square Example ( $N$ = normal, $n$ = recessive disease): * If both parents are heterozygous ( $Nn$ ): * Children: $25\%$ ( $NN$ ) (Normal), $50\%$ ( $Nn$ ) (Normal carrier), $25\%$ ( $nn$ ) (Affected).

Autosomal Dominant Identification: * Usually appears in every generation. * An affected person usually has an affected parent. * Approximately half of the children of an affected parent may be affected.
Autosomal Recessive Identification: * Can skip generations. * Parents may be unaffected carriers. * Multiple siblings in a single generation can be affected. * Males and females are affected with equal frequency.

Trait: White forelock is a dominant trait ( $F$ ).
Question G: If a chart shows three levels of descendants, $3$ generations are shown.
Individual C (Unshaded): If white forelock is dominant, an unshaded person ( $C$ ) must have the genotype ( $ff$ ).
Individual A (Shaded): A shaded individual ( $A$ ) expressing the dominant trait is most likely genotype ( $Ff$ ) if they have unaffected offspring.

Trait Details: * Dominant form ( $F$ ): Normal bone marrow function (no anemia). * Recessive form ( $f$ ): Falconi anemia (slow growth, heart defects, bone marrow failure, high rate of leukemia).
Genotypes: * Arlene: ( $ff$ ); she has Falconi anemia. * George: ( $Ff$ ); he does not have the disease, but he is a carrier because his children have the disease (they must have received an $f$ allele from him). * Carriers (Potential): Ann, Michael, Sam, Alan, and Daniel are likely carriers ( $Ff$ ).

Trait Details: * Dominant form ( $N$ ): Neurofibromatosis (abnormal neurofibromin protein). * Recessive form ( $n$ ): Normal protein.
Genotypes: * Individual #1: Heterozygous ( $Nn$ ). They have the trait, but some of their children do not ( $nn$ ), meaning the parent must carry the $n$ allele. * Individual #3: ( $nn$ ); they do not have the disease, which is dominant. * Affected Siblings of #3: Their genotypes cannot be determined with certainty; they could be ( $NN$ ) or ( $Nn$ ) since both parents are heterozygous.

Trait Details: Autosomal recessive ( $a$ ). Normal melanin is dominant ( $A$ ).
Scenario: Normally-pigmented parents have three children; the third (a girl) has albinism ( $aa$ ). She marries a normally pigmented male, and they have four children, the fourth of whom has albinism ( $aa$ ).
Logic: * The original parents must be ( $Aa$ ) (heterozygous carriers) to have an ( $aa$ ) child. * The girl with albinism ( $aa$ ) married a male who must be ( $Aa$ ) because they produced an ( $aa$ ) child. * The unaffected children are either ( $Aa$ ) or ( $A-$ ).

Trait Details: * Slow twitch muscles: homozygous recessive trait ( $ff$ ). * Fast twitch muscles: dominant ( $F$ ).
Case Analysis: * Individuals #3 and #4: Do not have slow twitch muscles (not shaded), yet they have a child with the trait ( $ff$ ). This implies both are heterozygous ( $Ff$ ). * Individual #8 or #9: They cannot be homozygous dominant if they have offspring with slow twitch muscles; they must be heterozygous ( $Ff$ ).

Lecture Date: 5/14/2026.
Online Quiz #13: Topics include Pedigrees.
Lab 13: Animal Diversity.
Lab Quiz #11: Animal Diversity Lab.
Lab Practical Exam: Tuesday, May 19th (Student Learning Objectives [SLOs] are posted).