Introduction to Genetics

Study Notes

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

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])

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

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

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 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

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

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

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