Introduction to Genetics

Introduction to Genetics

• Genetics is the science of heredity
• The word "Genetics" was coined by William Bateson in 1907
• In 1903, Walter Sutn and Theodor Boveri independently proposed that chromosomes carry hereditary factors
• The chromosomal theory of inheritance states that chromosomes contain DNA, which is the genetic material
• Gregor Mendel is considered the father of genetics

Learning Objectives (ILOs)

• Identify terminology in genetic medicine
• Compare codons and non-codons, mutations, and alleles
• List the steps of mitosis and meiosis
• Describe Mendel's laws
• Classify different chromosomal disorders

Human Genome

• By 2003, the DNA sequence of the entire human genome was known
• The human genome includes approximately 3 billion base pairs of DNA
• The genome includes coding regions that contain genes (approximately 20,000-25,000) and non-coding regions
• DNA is a collection of long polymers maintained in duplicate copies in every human cell
• DNA is encoded in its sequence of constituent bases (guanine [G], adenine [A], thymine [T], and cytosine [C])

Cell Cycle

• The cell cycle includes stages such as G1(growth), S (DNA synthesis), and G2 (growth)
• Mitosis is a process of cell division, where DNA and cytoplasm are divided to form two new cells. The steps include Prophase, Metaphase, Anaphase, and Telophase
• G0 is a resting state where the cell performs its functions and is not preparing for division
• Mitosis is the process whereby an animal cell which has previously replicated each of its chromosomes, separates the chromosomes in its cell nucleus into two identical sets of chromosomes, each set in its own new nucleus.
• Meiosis is used to produce sex cells such as eggs and sperm. It reduces the number of chromosomes from 46 (23 pairs) to 23 (single) -Meiosis I includes the steps Prophase I, Metaphase I, Anaphase I, and Telophase I
• Meiosis II includes the steps Prophase II, Metaphase II, Anaphase II, and Telophase II

Chromosomes

• Humans have 23 pairs of chromosomes (46 chromosomes)
• Chromosomes are thread-like structures made of DNA
• Chromosomes contain genes which determine an organism's characteristics and traits

Genes

• A gene is the basic unit of heredity and genetic information
• A gene is a specific nucleotide sequence that encodes for a specific protein
• A gene is comprised of two alleles
• Alleles is a variation form of a gene
• Alleles are either dominant or recessive.
• The genotype is the combination of alleles for a gene that leads to a phenotype

Mitosis and Meiosis

• Mitosis results in two diploid cells
• Meiosis results in four haploid cells

Mendelian Laws

• Law of Dominance: one allele dominates over another
• Law of Segregation: each gamete receives just one gene copy
• Law of Independent Assortment: alleles of different genes are sorted into gametes independently

Genetic Variances

• Genes can exist in different forms or states (alleles)
• Alleles differ in their nucleotide sequences

Genetic Disorders

• Genetic disorders are due to alterations or abnormalities in the genome of an organism
• Genetic disorders may be caused by a mutation in a single gene, multiple genes, or changes in chromosomes
• Genes are the basic unit of heredity
• Genes contain genetic information in the form of DNA
• Genes can mutate causing a change in the instructions to create the protein causing it to not work properly

Categories of Genetic Disorders

• Major chromosomal disorders
• Mendelian disorders
• Non-Mendelian disorders

Major Chromosomal Disorders

• Numerical abnormalities: Aneuploidy, Polyploidy, Monosomy, Trisomy, and Mosaicism
• Structural abnormalities: Translocation, Isochromosome, Inversions, Deletion, Insertions, and Ring Chromosome

Simple Mendelian Diseases

• Diseases that follow predictable patterns of simple transmission
• Genes involved are called causative genes
• The name reflects the fact that these diseases occur in simple patterns in families, and in most cases a single gene locus is the major determinant of the clinical disease phenotype
• Examples of autosomal dominant diseases: Huntington's disease, Myotonic dystrophy
• Examples of autosomal recessive diseases: Phenylketonuria, Sickle-cell anaemia, cystic fibrosis, Tay-sachs disease
• Examples of X-linked dominant disease: Rett syndrome
• Examples of X-linked recessive diseases: Hemophilia and color blindness

Multifactorial / Complex diseases

• Genetically complex diseases much more prevalent (over 1%)
• This type is the result of the interaction of multiple different gene loci, and environmental factors are important in the disease process.
• Example: Periodontitis

This quiz explores the fundamental concepts of genetics, including key terminology, the structure of DNA, and the principles of inheritance. You'll learn about the chromosomal theory, Mendel's laws, and the human genome. Test your knowledge on genetic medicine and chromosomal disorders.