3_Genetic Foundations of Development

Course Overview

  • Course Name: Genetic Foundations of Development

  • Instructor: Kelsey Kendellen, PhD

  • University: University of Lethbridge

Lecture Objectives

  • Describe how genes & chromosomes provide our basic genetic endowment.

  • Describe how the sex of a child is determined.

  • Explain the mechanisms by which genes transmit information.

  • Describe major inherited disorders produced by damaged or mutated genes.

Genes & Chromosomes: The Code of Life

  • Gametes: Organism’s reproductive cells or sex cells.

    • Male gametes = sperm cell.

    • Female gametes = ovum or egg cell.

    • Zygote = fertilized egg from the union of sperm & ovum.

  • Genes: The basic unit of genetic information.

    • Composed of specific sequences of DNA molecules.

    • Arranged in specific locations & order along chromosomes; determines the nature & function of every cell in the body.

  • Human genome: Entire set of genetic instructions in a cell; encoded as DNA; serves as a genetic blueprint.

    • Nucleus contains ~25,000 genes and 23 pairs of chromosomes.

    • Mitochondria contain 37 genes and have their own DNA (mtDNA).

Chromosomes

  • Chromosomes are thread-like structures in the nucleus.

  • Humans have 23 pairs of chromosomes (total of 46 chromosomes).

  • Egg & sperm cells each have 23 chromosomes.

  • Biological sex is determined by the 23rd pair of chromosomes (XX for females, XY for males).

  • Each gamete carries one chromosome from each pair.

Genotype vs Phenotype

  • Genotype: All a person’s genetic material (25,000 genes).

  • Phenotype: Observable characteristics or traits (physical and psychological).

    • Reflects the interaction of genotype and environment.

  • Epigenetics: Environment influences gene expression, leading to variability in traits.

    • Interaction of genes & environment is complex, not merely additive.

Mechanisms of Inheritance

  • Dominant and recessive genes:

    • Dominant genes expressed with recessive genes.

    • Recessive genes require both alleles to be present for expression.

  • Examples of dominant traits include brown eyes, dark hair.

    • Recessive traits include blue eyes, blond hair.

Sex-Linked Genes

  • Most mutated genes are recessive and can be sex-linked, located on X chromosome.

  • X-linked conditions predominantly affect males, as they have one X chromosome.

  • Female carriers (having one mutated allele) may not express the trait.

Polygenically Determined Characteristics

  • Characteristics influenced by multiple genes and the environment, e.g., height, weight, susceptibility to diseases (cancer, diabetes).

Genetic Variations

  • Genetic inheritance can involve abnormalities, categorized as:

    • Chromosome Variations: e.g., Down Syndrome (extra chromosome).

    • Gene-Linked Variations: e.g., cystic fibrosis (defects in a single gene).

Chromosome Variations: Down Syndrome

  • Trisomy 21: Three copies of chromosome 21.

  • Symptoms: Mild to severe intellectual disabilities, distinct physical features.

  • Incidence: 1 in 780 births.

Gene-Linked Variations: Examples

  • Cystic Fibrosis: Glandular dysfunction affecting mucus production; prevalent in 1 in 3,600 children.

  • Hemophilia: Delayed blood clotting.

  • Huntington's Disease: Central nervous system deterioration.

  • Phenylketonuria (PKU): Inability to metabolize phenylalanine; leads to intellectual disability.

  • Sickle-cell anemia: Blood disorder affecting oxygen supply.

Treatment and Incidence of Genetic Disorders

  • Cystic Fibrosis: Requires therapies for management; median survival ~57.3 years in Canada.

  • PKU: Requires special diet to manage phenylalanine levels for normal development.

  • Overall, early intervention and treatment strategies are crucial for hereditary disorders.