Understanding Mendelian Genetics
Mendelian genetics forms the foundation of our understanding of heredity and trait inheritance. This page introduces key concepts in Mendelian inheritance and provides tools for studying genetic patterns.
Definition: Mendelian inheritance refers to the inheritance of traits controlled by a single gene with two alleles, one of which may be completely dominant over the other (recessive) allele.
The pattern of inheritance depends on whether the gene is located on an autosome (the first 22 chromosome pairs in humans) or a sex chromosome (23rd chromosome pair in humans). This distinction is crucial for understanding different types of Mendelian inheritance.
Vocabulary: Alleles are variations or forms of a gene.
To study inheritance patterns, geneticists use two primary tools:
- Pedigrees: These charts show how traits are passed down through generations within a family.
Example: A pedigree chart is provided, showing symbols for males (squares) and females (circles), with affected individuals shaded. Vertical lines represent children of the previous generation, while horizontal lines connect breeding partners.
- Punnett Squares: These charts help determine the expected genotypic ratios of offspring from two parents.
Example: A Punnett square is shown for a cross between a homozygous dominant (RR) and homozygous recessive (rr) individual, resulting in 100% heterozygous (Rr) offspring.
Highlight: The pedigree example in the document illustrates autosomal dominant inheritance, one of the 3 types of Mendelian inheritance.
The page also references Mendel's famous pea plant experiments, which laid the groundwork for modern genetics. It shows an example of crossing plants with constricted and inflated pea pods, demonstrating how dominant and recessive traits are expressed in offspring.
Vocabulary: Genotype refers to the genetic makeup of an organism, while phenotype is the observable characteristic resulting from the genotype.
This comprehensive overview provides a solid foundation for understanding Mendelian genetics, including autosomal dominant, autosomal recessive, and X-linked inheritance patterns. The use of visual aids like pedigrees and Punnett squares makes these concepts more accessible to students studying genetic patterns of inheritance.
