Introduction to Genetics

Molecular Biology & Genetics 6105221

• Course instructor: Dr. Osama Essawi
• Office: HC 105 G
• Office hours: Monday/Wednesday 11:00–12:30, Tuesday 11:00–12:00

Text Book

• Genetics: A Conceptual Approach, 7th Edition
• Author: Benjamin A. Pierce

Introduction to Genetics

• Genetics is the study of genes, heredity, and variation in organisms.
• It explores how traits are passed from one generation to the next.
• Genetics provides insights into the mechanisms of inheritance and the characteristics of living organisms, from eye color to disease susceptibility.
• Heredity is the passing of genetic information from parents to offspring.
• Inheritance is how traits or characteristics are passed from generation to generation.

The Cell Theory

• Cell theory is a unifying biological theory universally accepted.
• All living organisms are made of one or more cells.
• All cells arise from other preexisting cells.
• All living organisms are made up of one or more cells.
• All cells arise from other, preexisting cells.

Cells, DNA, Genes, and Chromosomes

• Cells are the fundamental structural and functional units of living organisms.
• DNA (Deoxyribonucleic Acid) is the hereditary material of all known living organisms, encoding the genetic instructions for development and function.
• Genes are segments of DNA containing instructions for building and maintaining organisms.
• Chromosomes are structures composed of DNA and proteins found in the nucleus of eukaryotic cells.

Chromosome Structure

• Each chromosome consists of two chromatids (sister chromatids) connected by a centromere.
• Chromatids contain identical DNA sequences.
• Chromatids are formed during DNA replication.
• Each chromatid is made of a long, condensed DNA molecule that contains genetic information organized as genes.
• Chromosomes have protective structures at the ends called telomeres.
• The p arm is the shorter arm of a chromosome, and the q arm is the longer arm.

Fertilization and Chromosome Count

• Human egg cells typically have 23 unpaired chromosomes.
• Human sperm cells typically have 23 unpaired chromosomes.
• Fertilization results in a fertilized egg cell with 46 chromosomes in 23 pairs.

Homologous Chromosomes

• Diploid organisms have two sets of chromosomes organized as homologous pairs.
• Homologous chromosomes have the same length, gene location, and centromere position.
• A pair of homologous chromosomes each contains a set of alleles for a given gene.
• Each allele encodes a trait, such as eye or hair color.

Chromosome Types

• Eukaryotic chromosomes are categorized based on the position of the centromere.
• Submetacentric chromosomes: Centromere located slightly off-center.
• Metacentric chromosomes: Centromere located exactly in the center.
• Telocentric chromosomes: Centromere located at the very end.
• Acrocentric chromosomes: Centromere positioned near one end.

Karyotyping

• Karyotyping is a technique to analyze chromosome number, size, and structure.
• Used to detect chromosomal abnormalities like aneuploidy, translocations, and deletions.
• Cells are cultured and stopped at metaphase to capture condensed chromosomes.
• Chromosomes are stained to visibly distinguish their bands.

Karyotyping Process

• 1. Cell Culture: Stimulate cell division.
• 2. Metaphase Arrest: Stop cell division at metaphase.
• 3. Chromosome Staining: Visualize chromosome structure.

Identifying Chromosomes

• Identify chromosomes by size, banding pattern and centromere position.

G-Banding

• G-banding uses Giemsa stain to produce dark and light bands.
• Banding patterns are unique to each chromosome and can be used for identification.
• The format for identifying bands is typically "qXY" where X is the region and Y is the band.

G-Banded Metaphase Chromosomes

• A visual representation of chromosomes showing banding patterns to identify individual chromosomes.

Karyotype: Autosomes Vs sex chromosome

• A normal male karyotype is 46, XY.
• 46 represents the total number of chromosomes.
• XY represents the sex chromosomes.

Reasons for a Karyotype Analysis

• Issues with early growth and development.
• Cases of stillbirth or neonatal death.
• Fertility challenges.
• Family history of chromosomal abnormalities.
• Pregnancy in a woman of advanced age.

Genotype vs Phenotype

• Genotype: An individual's genetic makeup.
• Phenotype: Observable traits arising from the expression of the genotype.
• Phenotypes can be influenced by environmental factors.
• Wildtype is the most common phenotype in a natural population.

Homozygous vs. Heterozygous

• Homozygous: Having two identical alleles for a particular gene.
• Heterozygous: Having two different alleles for a particular gene.

Influence of Environmental Factors on Phenotype

• Environmental factors, such as temperature, can impact the expression of phenotypes.
• An example is Himalayan rabbits, where fur color changes in response to temperature.

Genes and Traits

• Genes are the hereditary units.
• Genes carry instructions for development.
• Alleles (different versions of a gene) contribute to trait diversity.

The Complexity of Genetic Information

• Genes can generate multiple proteins through alternative splicing.
• Proteins undergo modifications (e.g., phosphorylation, methylation).
• These factors lead to a large variety of protein functions beyond their genes.

Epigenetics

• Epigenetics studies heritable changes in gene function or expression without modifying the DNA sequence.
• DNA and histone protein modifications are involved.
• These changes can be affected by environmental factors.

Epigenetic gene regulation

• Histone modifications can activate or repress genes expression.
• Methylation or acetylation affect gene expression.

Glossary

• Defines key genetic terms, such as gene, allele, locus, genotype, and phenotype.