Mendelian Genetics Overview

Mendelian Genetics

• Inheritance is the transmission of traits from parents to offspring
• Gregor Mendel, through experiments with pea plants, discovered fundamental principles of inheritance.
• Mendel's principles are based on the idea that traits are determined by discrete units—now called genes—located on chromosomes.
• Genes can exist in different forms, called alleles.
• Alleles can be dominant or recessive, with dominant alleles masking the expression of recessive ones in heterozygotes.
• The law of segregation states that each individual possesses two alleles for each gene, and these alleles segregate (separate) during gamete formation, with each gamete receiving only one allele.
• The law of independent assortment states that alleles for different genes segregate independently of one another during gamete formation. This means the inheritance of one trait doesn't influence the inheritance of another. This only applies to genes on different chromosomes.
• Phenotype is the observable characteristic. Genotype is the genetic makeup.

Beyond Mendelian Inheritance

• Incomplete dominance: Heterozygotes show a blended phenotype, intermediate between the two homozygous phenotypes (e.g., pink flowers from red and white parents).
• Codominance: Both alleles are fully expressed in heterozygotes (e.g., AB blood type).
• Multiple alleles: A gene can have more than two alleles (e.g., human blood type).
• Polygenic inheritance: A single trait is controlled by multiple genes (e.g., human height).
• Pleiotropy: A single gene affects multiple traits (e.g., cystic fibrosis).
• Environmental influences: Environmental factors can modify the expression of genes (e.g., sun exposure affecting skin color).

Sex-Linked Inheritance

• Sex-linked genes are located on the sex chromosomes (X and Y).
• X-linked inheritance patterns differ between males and females due to the different sex chromosomes.
• Males, having only one X chromosome, express X-linked traits more frequently than females.
• Females are usually carriers for X-linked recessive traits, exhibiting them less often than males.
• Examples of X-linked traits include color blindness and hemophilia.
• Sex-linked recessive disorders are more common in males.

Chromosomal Basis of Inheritance

• Chromosomes carry genes in a linear order.
• Mitosis and meiosis are the processes of cell division involved in generating gametes and somatic cells, respectively.
• Meiosis is crucial for sexual reproduction as it results in gametes with half the number of chromosomes of the parent cell. This process contributes to genetic variation through crossing over and independent assortment.
• Non-disjunction during meiosis can lead to abnormal chromosome numbers in offspring. This has serious phenotypic consequences.
• Karyotypes can be used to visualize and analyze the number and structure of chromosomes in a cell.

Gene Interaction and Epigenetics

• Genes can interact in complex ways to produce a final phenotype. Interactions can occur at the protein level, or be more subtle.
• Epigenetics studies how environmental factors alter gene expression without changing the DNA sequence.
• Examples of epigenetic modifications include DNA methylation and histone modification; these can affect gene activity by altering accessibility to the DNA for transcription.
• Epigenetic modifications are potentially heritable and can influence traits across multiple generations.

Human Genetics

• Human genetics studies the inheritance of traits in humans.
• Genetic counselors help individuals understand their genetic risks and make informed reproductive decisions.
• Genetic testing allows for the identification of genetic conditions.
• Pedigree analysis tracks the inheritance pattern of a trait through generations.
• Genetic disorders can result from mutations in genes, leading to abnormal traits or conditions (e.g., cystic fibrosis, sickle cell anemia).
• Genetic technologies, such as CRISPR-Cas9, have the potential to treat genetic disorders.

Explore the foundational principles of Mendelian genetics, including inheritance patterns discovered by Gregor Mendel through his studies on pea plants. Understand concepts such as alleles, the law of segregation, and the law of independent assortment, which govern how traits are passed from parents to offspring.