Mendelian Genetics Quiz

Course Information

• Course name: Genetics Biology 202
• Semester: Spring 2025
• Instructor: Dr. Nancy Fujishige
• Office hours: Featherston Life Sciences Building 287, Mondays and Wednesdays 2:00-3:00 PM, or by appointment
• Zoom: By appointment only, https://lmula.zoom.us/j/796201568
• Email: [email protected]
• Materials: Slides and handouts are available online.

Introduction Assignment

• Students are asked to introduce themselves on Brightspace.
• Information includes: Preferred name, specific aspects of Genetics to study, relevant work experience, career plans, an interesting fact about themselves, and an optional picture.

Teaching Assistant (TA) Office Hours

• TAs: Hannah Kotek and Ashley Lee
• Days: Monday - Thursday
• Time: 6:00 PM - 8:00 PM

Class Strategy

• Problem solving: Breaking down problems into smaller parts
• Textbook readings and exercises
• Forming study groups
• Staying current with topics – progressively building upon prior knowledge
• Attending office hours if needed

Genetics in the News

• Highlights recent publications and articles in the field of genomics.
• Includes examples like FDA approval of a CRISPR treatment for sickle cell disease, Canada approving Pfizer's gene therapy for hemophilia, analysis of Gregor Mendel's DNA, and news about a 23andMe data breach case, as well as a story about DNA identification in a cold case. A variety of different aspects of the field are reviewed.

Today's Lecture

• Quick review of molecular biology
• What is genetics?
• Brief history of genetics
• Mendelian analysis (Mendel's experiments and laws)

Review - Familiar Concepts

• DNA structure and function
• Central dogma of molecular biology

Remember DNA Basics

• DNA is the genetic material of life
• 2 linear polymers of deoxyribonucleotide
• Each deoxyribonucleotide consists of a deoxyribose sugar, a phosphate group, and a nitrogenous base.
• The two polymers are antiparallel (5' to 3' and 3' to 5')
• Held together by hydrogen bonds (Adenine pairs with Thymine, Guanine pairs with Cytosine).

The Organization of DNA in a Cell

• Genome: the complete set of genetic material in a set of chromosomes
• Haploid (1n) and diploid (2n) – number of sets of chromosomes
• Chromosome: self-replicating structures that contain the DNA sequence of genes
• Gene: sequence of nucleotides located in a particular position on a chromosome encoding RNA or protein.

Central Dogma - In Action

• The central dogma summarizes how DNA is transcribed into RNA, and RNA is translated into proteins. This step is shown visually.

What is Genetics?

• Branch of biology focusing on heredity and variation.
• Explores the relationship between genes and traits.
• Explains life at the molecular, organ, and population levels.
• Explains biological phenomena (e.g., inheritance of traits, familial diseases, species extinction.)

Genetics Seeks to Explain

• What determines characteristics passed from one generation to the next?
• How are characteristics passed on?
• What are the rules governing trait transmission?

Next: A Brief History of Genetics

• Early hypotheses: homunculus, blending, Darwin's gemmules
• Mendel and his experiments
  • Background
  • Experiments with peas
  • Reciprocal crosses
  • Mendel's theory and Laws

History of Genetics

• For many millennia, people recognize familial resemblance, diseases running in families.

Homunculus

• Ancient belief that offspring are preformed inside sperm (or egg)

Blending Hypothesis

• Children are intermediate blend of parental traits.

Gemmules

• Darwin's theory of small particles inheriting from all parent organs.

Kolreuter

• 1840 realized parental traits can reappear after one generation.

Gregor Mendel

• Father of genetics
• Austrian monk
• 1822-1884

Mendel's Background

• Studied physics, math, and botany.
• Hybridization was a concern of his monastery and interested him.
• Focused on determining how genetic information is transmitted from one generation to the next.

He Brought Scientific Methods to the Study of Heredity

• Standardized methods inspired by physics: limiting variables, counting progeny, generating and testing models.
• Organized, verified and repeated experiments.
• Selected simple model systems for experiments.
• Measured/considered data across multiple generations.

Mendel Studied the Garden Pea

• Established breeding methods before Mendel.
• Traits: easily observable (ex. flower color, seed shape)
• Self or cross-pollination methods.

Peas Can Be Self or Cross-Fertilized

• Self-fertilization: pollen fertilizes ovules.
• Cross-fertilization: pollen from one plant fertilizes ovule of second plant

Mendel and blending & Gemmules

• Used self-pollination and cross fertilization
• Noticed traits could disappear and then reappear

Mendel's Characteristics of Hybrids

• Uniformity of phenotype
• Tendency to revert to parental phenotypes.

Mendel's Experimental Design

• Chose an excellent model system: Pisum sativum.
• Used "pure" or "true-breeding" lines.
• Studied several traits.
• Reciprocal crosses
• Followed progeny to F3 generation

Mendel's Breeding Experiment

• Results of monohybrid crosses (heterozygotes) of traits, dominant and recessive traits, ratios of phenotypes.

Conclusion from a Monohybrid Cross

• Phenotype ratios: purple and white in the F2 generation.
• Genotype ratios: PP, Pp, and pp

Molecular Basis for Appearance / Traits Encoded By Genes

• Heritable factors are genes.
• Genes are DNA segments that encode gene products (e.g. protein, tRNA, rRNA).
• Allele: different forms of the same gene.
  • Example: flower color – dominant or recessive alleles – for the trait.

Schematically: Allele/Gene/Genotype/Phenotype

• Allele: Different variations of a form within a gene (dominant or recessive)
• Dominant vs. Recessive alleles : Dominant trait is expressed over recessive trait
• Genotype: The allele pair for a gene within an organism
• Phenotype: The observable traits or characteristics expressed/visible due to presence and combination of alleles.

A link between Genotype and Phenotype

• Genotype linked with phenotype
• Phenotype visible traits

Let's go through the cross using this nomenclature.

• Explains how parents can be homozygous or heterozygous & related to traits, especially showing how recessive & dominant traits are apparent in later generations.

What Happens when a heterozygote Self-Pollinates

• Results of a monohybrid cross (Pp x Pp)
• Punnett Square results (determining genotypes and phenotypes.)
• Phenotype and genotypic ratios (ex. 3:1)

Conclusions from the Monohybrid Cross

• Monohybrid cross (Pp x Pp)
• Phenotypes and genotype ratios (ex. three purple for every white flower trait)