Mendelian Genetics and Intro to Statistics

LAB 7: Mendelian Genetics & Intro to Statistics

General Overview

  • Course: General Biology Laboratory (BIO 1111 74L)

  • Semester: Fall 2024

Introduction to Genetics

  • Definition of Genetics:

    • The study of how traits are inherited.

    • A trait is defined as a variation in the physical appearance of a heritable characteristic.

  • Purpose of Genetics:

    • To understand how traits are passed from generation to generation.

Historical Background: Gregor Mendel

  • Identity of Gregor Mendel:

    • An Augustinian friar from the mid-1800s.

    • Known as the “father of modern genetics.”

  • Contributions:

    • First to study genetics scientifically.

    • His goal was to understand inherited traits: the patterns in the way they are handed down from parents to offspring.

Mendel’s Experimental Model

  • Organism Used:

    • Pisum sativum (garden pea).

  • Methodology:

    • Crossed purebred plants with contrasting traits (e.g., tall vs. short height, seed color, flower color).

  • Observations:

    • Organisms inherit traits through genes, referring to discrete units of inheritance.

Genetic Information

  • Genes:

    • Organisms pass down traits through discrete units of inheritance.

    • Chromosomes contain blueprints for the body.

    • Definition of a Gene:

    • A segment of DNA that determines a trait.

Alleles

  • Definition of Alleles:

    • Variations of a gene that control the same trait.

  • Types of Alleles:

    • Dominant Allele:

    • Prevents the other allele from being expressed. Symbol: uppercase D.

    • Recessive Allele:

    • Not expressed even though it is present; requires two copies of the same allele for the trait to manifest. Symbol: lowercase d.

  • Homologous and Heterologous Alleles:

    • Homozygous:

    • Same allele inherited from each parent.

    • Examples: DD or dd.

    • Heterozygous:

    • Different alleles inherited from each parent.

    • Examples: Dd or dD.

Example: Flower Color Alleles

  • Dominant: P - purple

  • Recessive: p - white

  • Genotypes:

    • PP, Pp, pp.

Example: Hair Color

  • Gene for Hair Color Synonymous with Alleles:

    • R: non-red hair

    • r: red hair

  • Hypothesis Based on Offspring:

    • In the example given, 2 of the 4 kids have red hair. Hypothesis: Both parents are carriers of the recessive gene for red hair. New generation: All combinations of parents are denoted with Rr.

Punnett Square Example

  • Parental Genotypes: Rr x Rr.

  • Punnett Square:

    • RR

    • Rr

    • Rr

    • rr

  • Predicted offsprings: One of the four children should exhibit red hair (genotype: rr).

Statistical Analysis in Genetics

  • Chi-Square Analysis (X²):

    • Purpose: To determine whether the results are statistically significant, specifically if a relationship between variables is caused by something other than chance.

  • Formula for Chi-Square:

    • X^2 = \frac{(Obs. NON-RED - Exp. NON-RED)^2}{Exp. NON-RED} + \frac{(Obs. RED - Exp. RED)^2}{Exp. RED}

  • Example Calculation:

    • X^2 = \frac{(2 - 3)^2}{3} + \frac{(2 - 1)^2}{1} = \frac{1}{3} + 1 = 1.33

Null Hypothesis in Chi-Square Testing

  • Definition:

    • Hypothesis of no difference; variation in observed versus expected results is due to chance.

  • Interpretation of X² Value:

    • A lower value suggests that variations are likely due to chance.

    • X² = 1.33: Are these variations statistically significant, or could they merely result from random variation?

Degrees of Freedom (DoF)

  • Calculation of Degrees of Freedom:

    • One less than the number of observed phenotypes.

    • For example: 2 phenotypes (red and non-red hair) gives:

    • DoF = 2 - 1 = 1

  • Analysis of X² = 1.33:

    • Between 20% and 30%: Suggests observed differences can occur more than 20% of the time due to chance.

Decision on Null Hypothesis

  • Fail to Reject the Null Hypothesis:

    • Variations are attributed to chance.

  • Reject the Null Hypothesis:

    • Variations are due to other factors.

Blood Types

  • ABO Blood Group System:

    • Classifies human blood into four types based on antigens present on red blood cells (RBCs).

    • Types include:

    • A: A antigens on RBC with anti-B antibodies in plasma.

    • B: B antigens on RBC with anti-A antibodies in plasma.

    • AB: A & B antigens on RBC with no antibodies in plasma.

    • O: No antigens on RBC with A & B antibodies in plasma.

  • Role of Antibodies:

    • Attach to specific antigens and facilitate the immune response.

  • Agglutination:

    • The clumping of cells due to the presence of an antibody; crucial in determining blood type by mixing blood with anti-A or anti-B antibodies.