Lecture 33: Introduction to Genetics

Overview

• Covers Chapter 12 and 13 from Open Stacks textbook, focusing on genetics.
• Primary topics: Mendel's experiments, heredity, and modern understandings of inheritance.
• Lecture reorganizes these chapters for clarity, focusing on overall genetics.

Key Concepts in Genetics

Basic Terminology

• Chromosomes: Contain genes which are the instructions for making organisms.
• Genotype: The underlying genetic makeup of an organism; all genes together.
• Phenotype: Observable traits expressed by an organism (e.g., hair color, fur pattern).
• Relationship: Genotype leads to phenotype as genes encode proteins which determine traits.

Mendelian Inheritance

• Named after Gregor Mendel, an Austrian monk who experimented with pea plants.
• Alleles: Different versions of a gene (e.g., purple vs. white flower color in pea plants).
• Diploid Organisms: Have two copies of each chromosome and thus two alleles for each gene.

Types of Genotypes

• Homozygous: Two of the same allele (e.g., Homozygous dominant: AA, Homozygous recessive: aa).
• Heterozygous: Two different alleles (e.g., Aa).

Dominance in Alleles

• Dominant Allele: Expressed trait in heterozygous individuals (e.g., Purple is dominant over white in flowers).
• Recessive Allele: Only expressed when homozygous recessive.

Genetic Inheritance Patterns

Punnett Squares

• Predict possible genetic outcomes of offspring from parent genotypes.
• One gene is tracked at a time, using a grid to determine possible allele combinations.
• Example: Homozygous dominant crossed with homozygous recessive results in 100% heterozygous offspring.

Genetic Cross Examples

• Cross between two heterozygous individuals results in 25% homozygous dominant, 50% heterozygous, 25% homozygous recessive.
• Cross between heterozygous and homozygous recessive results in 50% heterozygous and 50% homozygous recessive.

Application to Humans

• Many human traits and diseases follow Mendelian inheritance (e.g., Huntington's disease, Cystic Fibrosis).

Conclusion

• The lecture introduced key genetic concepts and methods for predicting genetic inheritance.
• More genetics will be covered in future lectures.