BIOL 101 - Intro to Genetics Fall 2023

Introduction to Genetics

  • Overview of genetics and its significance in biology.

Gregor Mendel: The Father of Genetics

  • An Austrian monk and scientist studied the inheritance using pea plants in the 1860s.

  • Education: Studied biology, physics, and math at the University of Vienna.

  • Mentor-like role in monastery for teaching and research.

Pea Plants and Self-Fertilization

  • Pea plants possess both male (pollen) and female (ovule) gametes, enabling natural self-fertilization.

  • Mendel's method involved removing male structures from flowers for controlled hand-pollination, enabling precise breeding experiments.

Traits and Characters in Pea Plants

  • Character: An observable physical feature like seed shape, flower color, etc.

  • Trait: A specific form of a character (e.g., wrinkled or smooth seeds; purple or white flowers).

Mendel’s Experiments

  • Identified true-breeding plants for specific traits (e.g., crossing two true-breeding purple flower plants yields only purple offspring).

  • Created the parental generation (P) by crossing plants with differing traits, such as purple and white flowers.

Offspring Generations

  • The first filial generation (F1) results from parental crosses.

  • Mendel kept records of offspring expressing each trait to analyze inheritance.

  • Crossed members of the F1 generation to produce the second filial generation (F2).

Monohybrid Crosses

  • A hybrid is created by crossing parents with contrasting traits.

  • The F1 generation from monohybrid crosses consists of hybrids, highlighting the dominance of one trait over another.

Results of Monohybrid Crosses

  • Consistent results across 7 characters studied:

    • F1 generation displays only one trait while the other seems to disappear.

    • The hidden trait reappears in roughly 25% of the F2 generation, indicating a pattern.

Dominant and Recessive Traits

  • Each character had a dominant trait (expressed in all F1 plants) and a recessive trait (disappeared in F1).

  • The F2 generation exhibited a 3:1 ratio of dominant to recessive traits.

Genetics and Molecular Basis

  • Genetic information is stored in DNA within the cell nucleus on chromosomes.

  • Chromosomes house genes that dictate traits, with each gene containing instructions for protein synthesis.

Genes, Alleles, and Their Influence

  • A gene: a section of DNA on a chromosome coding for a specific protein (e.g., pigments).

  • An allele: different versions of a gene influencing specific trait expressions (e.g., variants for flower color).

Inheritance from Parents to Offspring

  • Chromosomes inherited from parents contain genes for determining traits.

  • Humans: 46 chromosomes arranged in homologous pairs; each pair contributes to the organism's traits.

Alleles and Genotypes

  • The trait displayed by an individual stems from its genotype, which is determined by the combination of alleles inherited from parents:

    • Homozygous: two identical alleles for a trait (e.g., AA or aa).

    • Heterozygous: two different alleles for a trait (e.g., Aa).

Phenotype vs. Genotype

  • Phenotype: the outward physical appearance influenced by genotype (e.g., flower colors).

  • Genotype influences phenotype depending on allele dominance and expression:

  • In homozygous individuals, phenotype matches genotype.

  • In heterozygous individuals, the dominant allele masks the recessive, displaying the dominant phenotype.

Gamete Formation and Segregation

  • Alleles are reorganized into gametes during meiosis, leading to cell division and formation of sperm/egg or pollen/ovule.

  • Mendel's law of segregation: alleles separate during gamete formation, ensuring offspring receive one allele from each parent, allowing predictions of inheritance patterns.

Punnett Squares and Predictions

  • Tools for predicting genotypes/phenotypes of offspring based on parental gametes: possible combinations fill the square representing offspring characteristics.

Functional vs. Nonfunctional Alleles

  • Dominant alleles produce functional proteins responsible for trait expression (e.g., pigment production).

  • Recessive alleles may produce nonfunctional proteins, leading to absence or alteration of traits in phenotype.

Inheritance Patterns in Humans

  • Mendel’s principles apply to human inheritance, where pedigrees demonstrate allele transmission through generations.

  • Dominant Trait Inheritance: Individual with one dominant allele expresses the trait (e.g., suspected linkage to affected parent).

Autosomal Dominant Disorders

  • Examples: Achondroplasia, Polydactyly, Huntington’s disease – conditions showcasing dominant traits.

Inheritance of Recessive Traits

  • Recessive gene carriers (Aa) can exhibit unaffected linkage (aa), allowing certain traits to skip generations.

  • Inheritance typically results in 25% affected offspring from two carrier parents.

Autosomal Recessive Disorders

  • Examples: Tay Sachs disease, Cystic fibrosis, Sickle cell anemia, indicating severe genetic disorders resulting from recessive alleles.

Tracking Rare Alleles

  • In small isolated populations, tracking rare alleles is simpler due to increased likelihood of carrier marriages leading to offspring with recessive disorders.

Polygenic Traits and Environmental Influence

  • Traits like hair and eye color are influenced by multiple genes, with more dominant alleles leading to darker colors.

  • Environmental factors (nutrition, health) also play a role in trait expression (e.g., height).

Mutation and Genetic Diversity

  • Mutations represent heritable changes in DNA, potentially leading to new alleles and traits.

  • If advantageous, new traits may spread in a population, guiding evolutionary processes (natural selection).