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.