Dominant vs Recessive Traits in Pedigrees

This page explores the differences between dominant and recessive traits as represented in pedigree charts, which is essential for pedigree genetics analysis.

Autosomal dominant pedigrees:

• Affected individuals appear in every generation
• At least one parent must be affected for a child to inherit the trait
• No generation skipping occurs

Autosomal recessive pedigrees:

• Affected individuals can appear even if parents are unaffected
• Traits can "skip" generations
• Carriers are usually not shown in these pedigrees

Example: In a recessive pedigree, you might see affected individuals in the third generation with unaffected parents, demonstrating the "skipping" of generations.

The page also introduces the naming convention for individuals in a pedigree:

• Roman numerals $I, II, III, IV$ indicate generations
• Arabic numerals $1, 2, 3$ identify individuals within a generation

Highlight: Determining genotypes from pedigrees requires careful analysis of shaded and unshaded shapes, considering the inheritance pattern.

The page concludes with examples of autosomal and sex-linked pedigrees, emphasizing the importance of understanding these differences for accurate genetic analysis.

Determining Genotypes in Dominant Pedigrees

This page focuses on how to analyze autosomal dominant pedigree charts to determine individual genotypes, which is crucial for pedigree analysis examples.

Key points for analyzing dominant pedigrees:

• Shaded shapes $affected individuals$ can be either homozygous dominant $AA$ or heterozygous $Aa$
• Unshaded shapes $unaffected individuals$ are always homozygous recessive $aa$
• Genotypes of some individuals may remain unknown due to limited information

Example: In a dominant pedigree, if an affected parent $Aa$ has a child with an unaffected parent $aa$, the child has a 50% chance of being affected $Aa$ and a 50% chance of being unaffected $aa$.

The page provides a detailed example of a dominant pedigree, demonstrating how to deduce genotypes based on parental information and offspring phenotypes.

Highlight: In dominant pedigrees, heterozygous individuals $Aa$ are still considered affected because the dominant allele is expressed in their phenotype.

The page also includes a Punnett square to illustrate the possible genotype combinations when a heterozygous individual $Aa$ mates with a homozygous recessive individual $aa$.

Vocabulary: Heterozygous refers to having two different alleles for a particular gene, while homozygous means having two identical alleles.

Determining Genotypes in Recessive Pedigrees

This page delves into the analysis of autosomal recessive pedigree charts, highlighting the differences from dominant pedigrees and providing guidance on determining genotypes in pedigrees.

Key characteristics of recessive pedigrees:

• Heterozygous individuals $Aa$ are carriers, often shown as half-shaded shapes
• Affected individuals are homozygous recessive $aa$
• Traits can appear to "skip" generations

Example: In a recessive pedigree, two unaffected carrier parents $Aa$ can have an affected child $aa$ with a 25% probability.

The page presents two types of recessive pedigree representations:

1. With carriers shown $half-shaded shapes$
2. Without carriers explicitly shown

Highlight: Even when carriers are not explicitly shown in a pedigree, their presence can be inferred based on the affected offspring or parental genotypes.

The page includes a detailed pedigree example with a key explaining the genotypes associated with different shape fillings:

• Filled in = aa $homozygous recessive$
• Empty = AA $homozygous dominant$
• Half filled = Aa $heterozygous$

Vocabulary: Phenotype refers to the observable characteristics of an organism, while genotype is the genetic makeup.

Autosomal vs Sex-linked Inheritance

This final page discusses the differences between autosomal and sex-linked inheritance patterns in pedigrees, which is crucial for comprehensive pedigree analysis examples.

Key points on sex-linked traits:

• Determined by genes on sex chromosomes $X or Y$
• Most commonly carried on the X chromosome
• Pedigrees show uneven distribution of affected individuals between genders

Definition: Sex-linked inheritance refers to the transmission of traits or diseases through genes located on the sex chromosomes.

Characteristics of sex-linked pedigrees:

• Usually show more affected individuals of one gender
• Often described as X-linked $female$ or Y-linked $male$ in genetic problems

Autosomal pedigrees:

• Show an even distribution of the trait among both males and females

Example: The page provides a pedigree chart demonstrating a sex-linked trait with more affected males than females.

Highlight: Understanding the difference between autosomal and sex-linked inheritance is crucial for accurate pedigree analysis and genetic counseling.

The page concludes with a visual representation of sex chromosomes $XX for females, XY for males$ to reinforce the concept of sex-linked inheritance.

Understanding Pedigree Charts

A pedigree chart is a visual representation of a family's genetic history, showing how traits or diseases are inherited across generations. This page introduces the basic symbols and concepts used in pedigree chart examples.

Definition: A pedigree is a chart that shows the inheritance of a trait or disease through multiple generations of a family.

Key elements of pedigree charts:

• Squares represent males, circles represent females
• Shaded shapes indicate affected individuals
• Unshaded shapes show unaffected individuals
• Half-shaded shapes represent carriers $in some cases$
• Horizontal lines connect parents
• Vertical lines show offspring

Vocabulary: Carriers are individuals who have one copy of a recessive allele but do not show the trait.

The page also explains how to read relationships in a pedigree:

• Siblings are shown by vertical lines branching from the same parents
• Parents are connected by a horizontal line

Highlight: Understanding pedigree symbols and relationships is crucial for analyzing inheritance patterns in genetics.