Patterns of Inheritance Lecture

Introduction

• Inheritance: How we inherit traits on chromosomes.
• Different patterns of inheritance.
• Gregor Mendel: First to study and publish on the topic, known as Mendelian genetics.

Chromosomes Overview

• 23 pairs of chromosomes.
  • 22 pairs are autosomes.
  • 23rd pair are sex chromosomes (XX or XY).
• Autosomal inheritance: Traits on the first 22 chromosomes.
• Sex-linked inheritance: Traits on the 23rd pair (sex chromosomes).

Important Concepts and Terms

• Alleles: Different versions of the same gene.
• Homozygous: Two of the same allele (e.g., GG or gg).
• Heterozygous: Two different alleles (e.g., Gg).
• Dominant vs. Recessive:
  • Dominant allele: Expressed in heterozygous individuals.
  • Recessive allele: Not expressed in heterozygous individuals.
• Genotype: The two alleles an individual has for a trait.
• Phenotype: Physical expression of the genotype.

Patterns of Inheritance

Complete Dominance

• One allele is completely dominant over another.
• Heterozygous individuals express the dominant phenotype.
• Autosomal recessive disorders:
  • Normal is dominant, disorder is recessive.
  • Example: Cystic Fibrosis.
• Autosomal dominant disorders:
  • Disorder is dominant, normal is recessive.
  • Example: Huntington’s disease.

Incomplete Dominance

• Heterozygous individuals have an intermediate phenotype.
• Example: Wavy hair from straight and curly hair.

Codominance

• Two alleles are not dominant over each other; both get expressed.
• Example: ABO blood type.
  • Type A and B markers.
  • O represents no markers.

X-linked Inheritance

• Traits inherited on the X chromosome.
• Different expression in males (XY) vs. females (XX).
• Examples: Colorblindness, Hemophilia.
• Key Points:
  • Females can be carriers if they have one normal and one affected X.
  • Males: Having one affected X leads to expression of the trait.

Problem Solving with Crosses

• Punnett Squares: Tool for predicting offspring outcomes.
• Heterozygous and homozygous crosses.
• Mono-hybrid crosses: Focus on one trait.

Practice and Examination

• Practice problems are crucial.
• Understand different patterns and be able to solve cross problems.
• Exam: Timed, requires understanding of cross outcomes.

Recap

• Autosomal vs. sex-linked inheritance.
• Dominant vs. recessive traits.
• Different patterns of inheritance and how to solve related problems.