Mendelian Genetics

Overview of Mendelian Genetics

• Mendelian genetics explains how traits are passed from parents to offspring through discrete units called genes.
• The "blending" hypothesis suggests traits mix like paint; the "particulate" hypothesis states traits are inherited as distinct units.

Mendel's Experiments

• Gregor Mendel conducted experiments with garden peas to formulate the laws of inheritance.
• Mendel hybridized true-breeding varieties, leading to the identification of dominant and recessive traits.

Key Concepts of Mendel's Model

• Alleles: Different versions of a gene, such as purple (dominant) and white (recessive) flower color.
• Law of Segregation: Alleles separate during gamete formation, ensuring each gamete carries only one allele for each trait.

Generations in Mendel's Experiment

• The P Generation consists of true-breeding parents.
• The first filial generation (F1) contains hybrid offspring from the P generation.
• Self-pollination of F1 plants leads to the second filial generation (F2).

Inheritance Ratios

• From Mendel's F2 generation, a 3:1 ratio of purple to white flowers was observed, indicating dominance of the purple flower trait.
• Mendel's research identified that recessive traits only appear in homozygous individuals.

Genetic Terminology

• Homozygous: An organism with two identical alleles (e.g., PP or pp).
• Heterozygous: An organism with two different alleles (e.g., Pp).
• Phenotype: The observable physical traits of an organism (e.g., purple flowers).
• Genotype: The genetic makeup of an organism (e.g., PP, Pp, or pp).

Applications of Punnett Squares

• Punnett squares predict the genetic outcomes of crosses between individuals.
• Dominant alleles are represented by capital letters (e.g., P) and recessive alleles by lowercase letters (e.g., p).

Disorders and Inheritance

• Recessively inherited disorders manifest only in individuals who are homozygous for the recessive allele.
• Carriers of recessive traits are heterozygous and do not express the condition, as seen in albinism.

Summary of Mendel's Contributions

• Established the foundational principles of heredity including allele variation, dominance and segregation.
• Mendel's work laid the groundwork for modern genetics, demonstrating predictable patterns of inheritance through systematic experimentation.### Overview of Mendelian Genetics
• Traits are passed from parents to offspring through discrete units known as genes, countering the "blending" hypothesis which suggested traits mix like paint.
• Gregor Mendel conducted experiments with garden peas to discover laws of inheritance.

Mendel's Experiments

• Utilized true-breeding varieties of pea plants to examine inheritance of traits, ensuring consistency in offspring.
• Crossed contrasting true-breeding parents (P generation) to produce hybrids (F1 generation); self-pollination of F1 produced the F2 generation.
• Noted dominant and recessive traits, where purple flowers (dominant) masked the expression of white flowers (recessive).

Mendel's Model of Inheritance

• Four key concepts explain inheritance patterns observed:
  • Alleles: Variations of a gene (e.g., purple and white flower color alleles).
  • Inheritance of Alleles: Organisms inherit two alleles for each trait, one from each parent. Alleles can be identical (homozygous) or different (heterozygous).
  • Dominance: In cases of differing alleles, the dominant allele determines appearance while the recessive has no visible effect.
  • Law of Segregation: Alleles segregate during gamete formation; each gamete receives one of the two alleles.

Punnett Squares

• A tool used to predict genetic crosses by illustrating potential combinations of alleles.
• Branded representations show dominant alleles with capital letters and recessive alleles with lowercase letters.

Genotype vs. Phenotype

• Genotype: Genetic makeup (e.g., PP, Pp for purple flowers).
• Phenotype: Physical appearance (both PP and Pp exhibit purple flowers).
• Different genotypes can lead to the same phenotype, complicating trait expression understanding.

Inheritance Patterns

• Phenotypic ratios in offspring can predictably arise:
  • From Pp x Pp crosses, a phenotypic ratio of 3 purple to 1 white occurs.
  • Genotype ratios can yield a 1:2:1 from the F2 generation concerning homozygous/heterozygous variations.

Recessive Disorders

• Disorders associated with recessive alleles appear only in homozygous individuals, whereas heterozygous individuals (carriers) may not display the condition.
• Example: Albinism is caused by a recessive allele leading to lack of pigmentation.

Test your knowledge on Mendelian Genetics with this quiz from BIO1101 Biology Department. Learn about the principles behind the passing of traits from parents to offspring and explore the debate between the "blending" hypothesis and the "particulate" hypothesis.