Lecture 12: Genetics PDF

Lecture 12: Genetics: a I. SEQ Mendels work A. SEQ MENDELS WORK B. CC COMPETING HYPOTHESES C. CC PRINCIPLES OF HEREDITY II. Genetic crosses A. SEQ,cc,,APPLY genetic crosses III. Using probability in genetics A. Apply probability rules Voca...

Lecture 12: Genetics: a I. SEQ Mendels work A. SEQ MENDELS WORK B. CC COMPETING HYPOTHESES C. CC PRINCIPLES OF HEREDITY II. Genetic crosses A. SEQ,cc,,APPLY genetic crosses III. Using probability in genetics A. Apply probability rules Vocabulary: Gene: Unit of heredity information. Allele: Alternative versions of a gene. Variation or form of a gene Character: Observable, heritable feature (e.g., hair color). Trait: Detectable variant of a character (e.g., red or blond hair). Genotype: Genetic makeup, what alleles are present. Combinations of Allels like “Bb” Phenotype: Observable physical traits. Example: Gene → Character: hair color. Allele → Trait: red hair. Gregor Mendel: Background: Austrian monk, known as the father of genetics. Contribution: Determined the basic rules of inheritance in eukaryotes, laying the foundation of genetics. Experimental Organism: Garden Pea: ○ Advantages: inexpensive, easy to obtain, easy to grow, identifiable traits, short generation time, easy to control pollination, many varieties available. ○ Collected 34 strains for experiments. Methodology:  Quantitative Methods: Kept detailed records of each step and recorded data. True Breeding Lines: ○ Definition: Always express the same trait after self-fertilization. ○ All express the same phenotype. ○ Mendel developed these lines over two years before starting experiments. Testing Blending Inheritance: Prevailing Idea in the 1800s: Gametes contain a mixture of fluids from parents that blend during reproduction. Blending Inheritance Prediction: Offspring should have an intermediate phenotype between the parents (e.g., mixing red and white results in pink). Mendel's Experiment: Crosses: Mated true-breeding plants (P generation) with contrasting traits. Generations: ○ P generation: Parental generation (grandparent). ○ F1 generation: First filial generation (children). ○ F2 generation: Second filial generation (grandchildren). Observations: F1 always resembled one parent (dominant trait). Traits absent in F1 reappeared in F2 in a 3:1 ratio. No intermediate phenotypes. Conclusion: Blending inheritance was incorrect. Mendel proposed particulate inheritance. Mendel's Model:  Particulate Inheritance: Characters are determined by heritable factors (genes). Each character has 2 factors (alleles), one from each parent. 4 Components of Mendel’s Model: 1. Alleles: Alternative versions of a gene. ○ Diploid individuals inherit 2 copies of each gene (one from each parent). ○ Alleles can be identical (as in true-breeding lines) or different. 2. Dominance: ○ If alleles differ, the dominant allele determines the phenotype. ○ The recessive allele has no noticeable effect. ○ Example: Flower color, Purple (P) is dominant over White (p). 3. Law of Segregation: ○ The 2 alleles for a character separate during gamete formation; each gamete receives 1 allele. 4. Law of Independent Assortment: ○ Genes on different chromosomes assort independently during gamete formation due to random orientation of chromosomes during metaphase I of meiosis. ○ Importance: Leads to genetic recombination and increased variation in offspring. Genetic Crosses:1 Purpose: Predict the genotype of offspring by tracking allele behavior. Crosses: Determine possible gametes based on the parent genotype. Monohybrid Cross: Cross between heterozygotes (e.g., Yy x Yy). F1 Generation: ○ Genotype: Yy (heterozygous). ○ Phenotype: Dominant (e.g., yellow seed color). F2 Generation: Cross F1 individuals (Yy x Yy). Punnett Square Example: Y y Y YY Yy y Yy yy Genotype Ratio: 1 YY : 2 Yy : 1 yy (1:2:1). Phenotype Ratio: 3 Yellow : 1 Green (3:1). Ratio results from the segregation of alleles during meiosis. Monohybrid Test Cross: Purpose: Identify genotype of an individual with a dominant phenotype. Example: Cross a Yellow (Y-) F2 individual with a homozygous recessive (yy) to determine if it is YY or Yy.