Genetics: Basics of Inheritance and Mendelian Laws

• Genetics is the study of heredity and variation in living organisms

Basics of Inheritance

• Genes are the basic units of heredity, composed of DNA and encoding specific traits
• Alleles are different versions of a gene
• Genotype is the genetic makeup of an organism
• Phenotype is the observable characteristics of an organism, resulting from the interaction of its genotype and the environment
• Homozygous means having two identical alleles for a gene
• Heterozygous means having two different alleles for a gene
• Dominant alleles mask the expression of recessive alleles in heterozygous individuals
• Recessive alleles are only expressed when an individual is homozygous for them

Mendelian Genetics

• Gregor Mendel's experiments with pea plants laid the foundation for modern genetics
• Mendel's laws include:
  • Law of Segregation: Each individual has two alleles for each trait, and these alleles separate during gamete formation, with each gamete receiving only one allele
  • Law of Independent Assortment: Genes for different traits assort independently of each other during gamete formation, provided they are not linked on the same chromosome

Chromosomes

• Chromosomes are structures made of DNA and proteins that carry genetic information
• Humans have 46 chromosomes arranged in 23 pairs
• Autosomes are non-sex chromosomes (22 pairs in humans)
• Sex chromosomes determine the sex of an individual (X and Y chromosomes)
• Karyotype is the complete set of chromosomes in a cell or organism

DNA Structure and Function

• DNA (deoxyribonucleic acid) is a double-stranded helix composed of nucleotides
• Each nucleotide consists of a deoxyribose sugar, a phosphate group, and a nitrogenous base
• The four nitrogenous bases in DNA are adenine (A), guanine (G), cytosine (C), and thymine (T)
• A pairs with T, and C pairs with G (Chargaff's rules) through hydrogen bonds
• DNA replication is the process by which DNA makes copies of itself
• DNA replication is semi-conservative, meaning each new DNA molecule consists of one original strand and one newly synthesized strand
• The enzyme DNA polymerase is responsible for synthesizing new DNA strands
• DNA carries the genetic code, which is the set of rules by which information encoded in genetic material (DNA or RNA sequences) is translated into proteins by living cells

RNA Structure and Function

• RNA (ribonucleic acid) is a single-stranded molecule similar to DNA
• RNA contains ribose sugar instead of deoxyribose sugar, and uracil (U) instead of thymine (T)
• Messenger RNA (mRNA) carries genetic information from DNA to ribosomes
• Transfer RNA (tRNA) brings amino acids to the ribosome during protein synthesis
• Ribosomal RNA (rRNA) is a component of ribosomes

Gene Expression

• Gene expression is the process by which the information encoded in a gene is used to synthesize a functional gene product (protein or RNA)
• Transcription is the process of copying a gene's DNA sequence into RNA
• RNA polymerase is the enzyme responsible for transcription
• Translation is the process of using mRNA to synthesize a protein
• Ribosomes are the site of translation
• Codons are sequences of three nucleotides in mRNA that specify which amino acid should be added to the growing polypeptide chain
• The start codon (AUG) initiates translation, and the stop codons (UAA, UAG, UGA) terminate translation

Mutations

• A mutation is a change in the DNA sequence
• Mutations can be spontaneous or induced by mutagens (e.g., radiation, chemicals)
• Point mutations are changes in a single nucleotide base
  • Substitutions: Replacement of one nucleotide by another
  • Insertions: Addition of one or more nucleotides
  • Deletions: Removal of one or more nucleotides
• Frameshift mutations result from insertions or deletions that alter the reading frame of the genetic code, leading to a completely different protein sequence
• Chromosomal mutations involve changes in the structure or number of chromosomes
  • Deletions: Loss of a chromosome segment
  • Duplications: Repetition of a chromosome segment
  • Inversions: Reversal of a chromosome segment
  • Translocations: Movement of a chromosome segment to a non-homologous chromosome
• Mutations can be harmful, beneficial, or neutral depending on their effect on the function of the gene or protein

Genetic Engineering

• Genetic engineering involves manipulating an organism's genes to introduce, eliminate, or modify specific traits
• Recombinant DNA technology is used to create new combinations of genetic material
• Restriction enzymes cut DNA at specific sequences
• DNA ligase joins DNA fragments together
• Plasmids are small, circular DNA molecules used as vectors to carry foreign DNA into host cells
• Polymerase chain reaction (PCR) is a technique used to amplify specific DNA sequences
• Gene therapy involves introducing genes into cells to treat or prevent disease
• Genetically modified organisms (GMOs) have been engineered to have specific traits, such as resistance to pests or herbicides

Population Genetics

• Population genetics is the study of genetic variation within and among populations
• Gene pool is the total collection of genes in a population
• Allele frequency is the proportion of a specific allele in a population
• Hardy-Weinberg principle describes the conditions under which allele and genotype frequencies in a population will remain constant from generation to generation
  • No mutation
  • Random mating
  • No gene flow
  • No genetic drift
  • No selection
• Deviations from Hardy-Weinberg equilibrium indicate that evolutionary forces are acting on the population
• Genetic drift is random changes in allele frequencies due to chance events, particularly significant in small populations
• Gene flow is the movement of genes between populations
• Natural selection is the process by which individuals with certain heritable traits survive and reproduce at a higher rate than others, leading to changes in allele frequencies over time

Epigenetics

• Epigenetics is the study of heritable changes in gene expression that do not involve alterations to the DNA sequence itself
• DNA methylation is the addition of a methyl group to a DNA base (usually cytosine), which can repress gene transcription
• Histone modification involves chemical modifications to histone proteins, which can affect chromatin structure and gene expression
• Epigenetic modifications can be influenced by environmental factors, such as diet, stress, and exposure to toxins
• Epigenetic changes can be passed on to future generations, influencing their phenotype without altering the DNA sequence

Genomics

• Genomics is the study of entire genomes, including the structure, function, evolution, and mapping of genes
• Genome sequencing involves determining the complete DNA sequence of an organism
• Comparative genomics involves comparing the genomes of different species to understand evolutionary relationships and identify genes involved in specific traits
• Functional genomics aims to understand the function of genes and other genomic elements
• Proteomics is the study of the complete set of proteins produced by an organism

Explore the fundamental concepts of genetics, including genes, alleles, genotypes, and phenotypes. Learn about Mendelian genetics and the laws of segregation and independent assortment. Understand how these principles govern the inheritance of traits in living organisms.