Introduction to Genetics

Introduction to Genetics

• All living organisms need to reproduce to continue their species
• Offspring inherit genetic information from parents, ensuring the continuation of the species
• DNA is organized into functional units called genes, which are part of larger structures called chromosomes
• The complete set of genetic material in a cell is called a genome
• Genetics is the study of genes, with significant impact on daily life (e.g., genetic counseling, insulin production)
• Human reproduction is sexual, combining genetic material from two parents to create genetically unique offspring
• The Human Genome Project mapped all chromosomes and genes, crucial for understanding and treating inherited diseases
• Ageing has an impact on chromosomes, cell division, and heredity, discussed in the text

Chromosomes, Genes, and DNA

• Chromosomes are numbered, largest being number 1.
• The first 22 pairs are called autosomes, and they have the same amount of genetic material in each
• The 23rd pair are sex chromosomes (X and Y), they determine gender and are not necessarily the same size
• Human cells have 46 chromosomes (23 pairs) arranged as a Karyotype
• Nearly every body cell has an identical copy of the entire genetic material; this material is called chromatin
• Chromosomes are visible structures during cell division that compact genetic material in cells.
• Chromosomes are composed of DNA coiled around proteins called histones
• Chromosomes are capped with a section of DNA called telomeres
• Telomeres help seal the chromosome and are important in replication
• Telomerase helps repair shortened telomeres

DNA

• DNA is double-stranded, made of two chains of nucleotides
• Nucleotides consist of sugar, a phosphate, and a base
• DNA bases paired are: Adenine pairs with Thymine; Guanine pairs with Cytosine
• DNA structure is a double helix
• DNA is a twisted ladder structure formed by alternating sugar and phosphate units
• Each base binds to a specific complementary base on the opposite strand
• The bases pair to create a specific code that carries genetic information
• Some 99% of DNA does not code for proteins but signals start and stop for protein synthesis
• The human genome has about 20,500 genes
• Genes exist in pairs, one inherited from each parent
• DNA's sequence carries genetic instructions crucial for organismal activities and inheritance

Genes

• Genes are the fundamental unit of heredity
• Genes are sections of DNA
• Genes can be dominant or recessive
• Some genes can have multiple alleles to code for specific traits

Protein Synthesis

• Protein synthesis involves two main steps, transcription and translation
• Transcription copies genetic information in DNA into a messenger RNA (mRNA) molecule
• Translation uses mRNA information to synthesize proteins by linking amino acids
• Proteins are essential for all aspects of bodily functions, structural and enzymatic

Cell Division

• Mitosis produces two identical diploid daughter cells
• Meiosis produces four genetically different haploid daughter cells
• DNA replication happens before both mitosis and meiosis
• Cell division plays a vital role in growth, repair, and producing gametes (sperm and eggs), essential for continued reproduction

Gene Expression

• Gene expression refers to the use of specific genes for particular functions of cells, and involves turning genes on and off
• This variation depends on the cell's function
• All nucleated cells except gametes start with an identical set of genes
• Gene expression ensures cells develop differently, expressing only necessary genes to perform their task

Genetic Basis of Human Inheritance

• Autosomal inheritance explains how traits are passed through dominant and recessive genes
• Co-dominance describes traits with more than two alleles (e.g., blood types)
• Sex-linked inheritance involves traits carried on the X or Y chromosomes (examples: color blindness, hemophilia)

Cancer

• Cancer is caused by mutations in cellular DNA leading to uncontrolled cell growth
• Mutations can be inherited or acquired through age or other factors
• Cells acquire mutations that give properties of cancer cells
• The occurrence of cancer increases with age

Aging and Genetics

• Cumulative exposure to mutagens and declining DNA repair mechanisms lead to mutations
• Telomeres and telomerase function declines and impacts cell division and repair mechanisms
• Mutations in mitochondria DNA impact cell function

Chromosomal Abnormalities

• Abnormalities occur due to errors during meiosis leading to incorrect number of chromosomes
• Disorders caused by errors in the number and structure of chromosomes include Turner's and Klinefelter's syndromes, Down syndrome, and Cri-du-Chat syndrome

Genetic Diseases

• Inherited diseases arise from mutated genes
• Examples of genetic diseases with examples mentioned in the text are Phenylketonuria, cystic fibrosis, hemophilia and muscular dystrophy